text:
|Publication number
|Publication type
|Application number
|Publication date
|Mar 21, 2006
|Filing date
|Nov 1, 2001
|Priority date
|Mar 19, 1996
|Fee status
|Also published as
|Publication number
|Chrysanthos Nicholas Dellarocas, Thomas W. Malone
|Original Assignee
|Massachusetts Institute Of Technology
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (4), Non-Patent Citations (2), Referenced by (87), Classifications (4), Legal Events (2)
|External Links: USPTO, USPTO Assignment, Espacenet
This application is a Continuation of prior application No: 08/958,142, file on Oct. 28, 1997, entitled COMPUTER SYSTEM AND COMPUTER IMPLEMENTED PROCESS FOR REPRESENTING SOFTWARE SYSTEM DESCRIPTIONS AND FOR GENERATING EXECUTABLE COMPUTER PROGRAMS AND COMPUTER SYSTEM CONFIGURATIONS FROM SOFTWARE SYSTEM DESCRIPTIONS, and now pending.
This application is a continuing application which claims the benefit under 35 U.S.C. �120 of application Ser. No. 08/820,913, filed Mar. 19, 1997, now abandoned and under �119(e) of prior provisional application Ser. No. 60/013,694, filed Mar. 19, 1996, which are hereby incorporated by reference.
The Government of the United States of America has certain rights in this invention as provided for by the terms of Contract No. IRI-9224093 awarded by the National Science Foundation.
The present invention is related to computer systems and computer implemented processes which allow a user to define representations of software systems. The present invention is also related to computer systems for storing multiple alternate implementations of computer programs. The present invention is also related to computer systems and computer implemented processes for generating computer program code from a high level description of a software system.
The design and specification of software systems has been studied from many perspectives. Research in software architectures has lead to several languages for architectural description of software systems, including representing architectural taxonomies and specific software architectures.
Software development research has provided a variety of approaches to building software systems, including module interconnection languages, open software architectures such as software bus architectures, object oriented programming, coordination languages and application frameworks. An application framework includes an application programming interface and a set of protocols that guide the way calls to the application programming interface should be used inside components. Research in software reuse has also resulted in the development of software schemas such as the Programmer's Apprentice, and program transformation systems which translate programs between computer programming languages.
Other areas of research in software development include operating systems and concurrent and distributed systems. Additionally, numerous computer related software engineering tools, i.e., automated tools that support various phases of software design and development, also have been developed.
The present invention applies coordination theory to the representation of software systems. Coordination theory focuses on the interdisciplinary study of the process of managing dependencies among activities, in particular, business processes, operation research, organization theory, economics, linguistics, psychology and computer science. Coordination theory has been used as the basis for a representation and design of business processes in a process handbook, as described in PCT publication WO94/19742, published Sep. 1, 1994, also incorporated by reference. This reference does not discuss entities such as ports and resources as described below and how to generate executable code or system configurations from process representations.
Current programming languages and computer system design tools fail to recognize component interaction as a separate design problem, orthogonal to the specification and implementation of the core function of a component. That is, many software components have the built in assumptions about coordination, interoperability and architectural characteristics. Given a set of software components, designers typically either have to modify the code of existing components or have to write additional coordination software that bridges mismatches among components. Such mismatches include low level interoperability mismatches, such as differences in expected and provided procedure names, parameter orderings, data types, calling conventions and other interface mismatches. Another kind of mismatch is an architectural mismatch, such as different assumptions about the architecture of the application in which the components appear. Such mismatches include differences in expected and provided communications protocols, different assumptions about resource ownership and sharing, different assumptions about the presence or absence of particular operating system and hardware capabilities, etc. As design moves closer to implementation, current programming tools increasingly focus on representing components. At the implementation level, software systems are sets of source and executable modules in one or more programming languages. Although modules come under a variety of names and flavors, e.g., procedures, packages, objects and clusters, etc., they are all essentially abstractions for components.
By failing to provide separate abstractions for specifying and implementing interconnection protocols among software components, current programming languages force programmers to distribute such protocols among the interdependent components. As a consequence, code-level components encode, apart from their ostensible function, fragments of interconnection protocols from their original development environments. These fragments translate into a set of undocumented assumptions about their dependencies with the rest of the components in a system. When attempting to reuse components in new applications, such assumptions have to be identified manually and modified, in order to match the new interdependency patterns at the target environment. This often requires extensive modifications of existing code, or the development of additional coordination software.
To this date, there has been no uniform framework for describing the various kinds of component mismatches, or systematic set of rules for dealing with them. Designers generally rely on their own intuition and experience and the problem of component composition is still being confronted in a largely ad-hoc fashion.
The present invention provides a mechanism for easily integrating existing software components into new applications. It is based on a recognition that a computer software system includes interdependent collections of software components. That is, at the architectural level, software components and their interdependencies are two distinct and equally important entities. The software components represent the core functional pieces of an application and deal with concepts specific to an application domain. Interdependencies relate to concepts which are orthogonal to the problem domain of most applications, such as transportation, sharing of resources and synchronization constraints among components.
An architectural design language is provided which has linguistic support for representing and transforming software architecture diagrams. This language enables a clear separation of the core functional pieces of an application, herein called activities, and their interconnection relationships in context of the application, herein called dependencies. The language also supports entity specialization, a mechanism through which software architectures can be described at various levels of abstraction.
In addition, a design handbook of dependency types and associated coordination processes is provided. Such a handbook is based on the observation that many interconnection problems and software applications are related to a relatively narrow set of concepts, such as resource flows, resource sharing, and timing dependencies. These concepts are orthogonal to the problem domain of most applications, and can therefore be captured in an application independent vocabulary of dependency types. Similarly, the design of associated coordination processes involves a relatively narrow set of coordination concepts, such as shared events, invocation mechanisms, and communication protocols. Therefore, coordination processes can also be captured in a design space that assists designers in designing a coordination process that manages a given dependency type, simply by selecting the value of a relatively small number of design dimensions. The design handbook combines the vocabulary of dependencies in a design space of coordination processes. Such a handbook may reduce the specification and implementation of software component interdependencies to a routine design problem, capable of being assisted, or even automated, by computer tools.
A process for constructing and transforming architectural diagrams of software architectures to integrate executable design elements into code modules is also provided. The process involves applying a series of transformations to an architectural description of a target application. This architectural description may be defined in the architectural design language provided above. Generally speaking, the transformation process includes constructing application architecture diagrams, interactively specializing generic activities, interactively managing unmanaged dependencies between the activities using coordination processes from the design handbook, and integrating executable design elements into code modules.
As a result, the architectural design language, design handbook and transformations provide a system which can accurately and completely describe nontrivial applications and facilitate code-level and architectural-level software reuse.
Accordingly, one aspect of the present invention is an architectural description language which represents activities and dependencies between activities as separate entities. Dependencies are managed by coordination processes associated with the dependency. Activities and dependencies are connected through ports which encode interfaces between activities and coordination processes. The language may also represent resources which may be understood as the outputs of activities that are beyond the scope of the defined software system. Each entity, i.e., activity, dependency, port or resource, may also have attributes which are name value pairs, specifying additional information about the entity. Attributes may be inherited. That is, activities and dependencies may be specialized into particular versions of an activity or dependency. The attributes for a particular activity are inherited by its specializations.
Another aspect of the invention is a computer system which allows a user to define a software system specification, or entities thereof, in the architectural description language in terms of activities and dependencies and their interconnections through ports.
Another aspect of the invention is a computer system which permits entities in this architecture description language to be combined.
Another aspect of the invention is a computer system which checks for compatibility of connected entities in the architectural description language.
Another aspect of the invention is a computer system for storing and accessing stored representations in the architectural description language, including specializations and decompositions of selected representations.
Another aspect of the invention is a computer system which receives definitions of a computer system in terms of its activities, dependencies and ports indicating their connections and specializes a description of generic component elements.
Another aspect of the invention is a computer system which receives a definition of a software system in terms of its activities, dependencies and ports and which decouples dependencies which cannot be managed independently of other dependencies to generate another definition of the software system.
Another aspect of the invention is a computer system for storing a library of coordination processes, including a representation of specific computer programs, each of which is a specialization of a process for managing a dependency, such as resource sharing dependencies, flow dependencies and timing dependencies. It should be understood that there are many types of dependencies, of which the following description includes particular examples. The various combinations of one or more of these example dependencies is an aspect of this invention.
Another aspect of the invention is a computer system which generates executable computer program code from specialized generic software component elements described as combinations of activities, and dependencies having ports for interconnection.
Other aspects of the invention include the various combinations of one or more of the foregoing aspects of the invention, as well as the combinations of one or more of the various embodiments thereof as found in the following detailed description or as may be derived therefrom. It should be understood that the foregoing aspects of the invention also have corresponding computer-implemented processes which are also aspects of the present invention. It should also be understood that other embodiments of the invention may be derived by those of ordinary skill in the art both from the following detailed description of a particular embodiment of the invention and from the description and particular embodiment of a system in accordance with the invention.
The various aspects of the invention enable reuse of code-level components. Designers can generate new applications simply by selecting existing components to implement activities, and coordination processes to manage dependencies, independently of one another. The development of successful frameworks for mapping dependencies to coordination processes reduces the step of managing dependencies to a routine one, and enables it to be assisted or even automated by design tools. Overall, new applications can be generated with minimal or no need for user-written coordination software.
The various aspects of the invention also enable reuse of software architectures. Designers can reuse the same architectural description in order to reconstruct applications after one or more activities have been replaced by alternative implementations. A designer simply may semi-automatically remanage the dependencies of the affected activities with the rest of the system. Furthermore, designers may reuse the same set of components in different execution environments by managing the dependencies of the same architectural description using different coordination processes, appropriate for each environment.
The various aspects of the invention also enable insight into software organization alternatives. The description of software applications as sets of components interconnected through abstract dependencies may help designers to structure their thinking about how to best integrate the components together. A design space of coordination processes for managing interdependency patterns may assist them to explore alterative ways of organizing the same set of components, in order to select the one which exhibits optimal design properties.
In the drawing,
The present invention will be more completely understood through the following detailed description which should be read in conjunction with the attached drawing in which similar reference numbers indicate similar structures.
Referring now to
The process repository 30 is connected, as shown by arrows 31, to other applications as shown in
Another tool is a code and configuration generator 44 which transforms process descriptions into executable program code, configurations of enterprise software packages, workflow systems or object frameworks. This code generator also facilitates reuse of software components and can be used for rapid prototyping of software applications from existing software components. A similar tool is a process model translator 52 which translates a process description into a description in another language, such as for a computer aided software engineering (CASE) application program 56 or other modeling tools 58. As will be described below, the process representation used in the present invention defines an architectural description language and can be readily translated to other formats using standard parsing techniques.
The user interface clients 40 typically provide for retrieval and viewing of process descriptions, such as a process viewer 46 typically using a browser interface such as an HTML browser or a drawing tool, such as VISIO from Shapeware Corporation. More functionality may be provided by a design assistant 48 which permits a user to see various decompositions and specializations of a process, in particular for comparison and selection of processes that implement coordination processes as described below. Other client programs, such as a process handbook navigator may be used to view processes, their decompositions and their various specializations, particularly enabling comparison of alternative processes for performing a task.
A computer system which may be used to implement the present invention will now be described in connection with
It should be understood that one or more output devices may be connected to the computer system. Example output devices include a cathode ray tube (CRT) display, liquid crystal displays (LCD), printers, communication devices such as a modem, and audio output. It should also be understood that one or more input devices may be connected to the computer system. Example input devices include a keyboard, keypad, track ball, mouse, pen and tablet, communication device, audio input and scanner. It should be understood the invention is not limited to the particular input or output devices used in combination with the computer system or to those described herein.
The computer system may be a general purpose computer system which is programmable using a high level computer programming language, such as "C, or "Pascal." The computer system may also be specially programmed, special purpose hardware. In a general purpose computer system, the processor is typically a commercially available processor, of which the series x86 processors, available from Intel, and the 680X0 series microprocessors available from Motorola are examples. Many other processors are available. Such a microprocessor executes a program called an operating system, of which UNIX, DOS and VMS are examples, which controls the execution of other computer programs and provides scheduling, debugging, input/output control, accounting, compilation, storage assignment, data management and memory management, and communication control and related services. The processor and operating system define a computer platform for which application programs in high-level programming languages are written.
The memory system 62 in a typical general purpose computer system usually includes a computer readable and writeable nonvolatile recording medium, of which a magnetic disk, a flash memory and tape are examples. The disk may be removable, known as a floppy disk, or permanent, known as a hard drive. A disk has a number of tracks in which signals are stored, typically in binary form, i.e., a form interpreted as a sequence of one and zeros. Such signals may define an application program to be executed by the microprocessor, or information stored on the disk to be processed by the application program. Typically, in operation, the processor causes data to be read from the nonvolatile recording medium into an integrated circuit memory element, which is typically a volatile, random access memory such as a dynamic random access memory (DRAM) or static memory (SRAM). The integrated circuit memory element allows for faster access to the information by the processor than does the disk. The processor generally manipulates the data within the integrated circuit memory and then copies the data to the disk when processing is completed. A variety of mechanisms are known for managing data movement between the disk and the integrated circuit memory element, and the invention is not limited thereto. It should also be understood that the invention is not limited to a particular memory system.
It should be understood the invention is not limited to a particular computer platform, particular processor, or particular high-level programming language. Additionally, the computer system 20 may be a multiprocessor computer system or may include multiple computers connected over a computer network.
Referring again to
The architectural description language clearly separates core functional pieces of an application from their application specific patterns of interdependencies. This separation can be provided by supporting two distinct language elements: activities, for representing a core functional parts and dependencies, for representing interconnection relationships among activities.
The language also separates the specification of the system architecture from the implementation of the elements being structured. In particular, activities may be associated with an optional code level component, such as a source code module, an executable program, or a network server. Similarly, dependencies can be associated with an optional coordination process, representing a protocol for managing the relationship described by the dependency. Such a separation enables components for implementing activities to be selected or replaced independently of one another. This independence is possible because the specification level interdependencies do not change. However, different component implementations might influence the implementation of interaction protocols. This separation also allows an application to be ported to different configurations. Again, this portability is possible because specification level relationships of activities do not change. Rather, the implementation of interaction protocols is most likely to change across configurations.
This architectural inscription language also makes it possible to connect the specification of a system architecture to the implementation of the elements being structured through well-defined structural transformations. As a result, executable applications can be generated directly from a software architectural diagram, as will be described in more detail below. In one embodiment of the invention, a mechanism herein called entity specialization allows generic application architectures to be transformed to executable systems by selection of successively specialized activities and dependencies contained in the architectural decomposition.
The architectural description language also supports the specification and confirmation of compatibility restrictions and configuration constraints on the interconnection of the application elements. That is, when connecting or transforming language elements in an architectural description, a limited static checking of compatibility of these elements is performed, similar to type checking in programming languages. This capability facilitates the construction of correct architectural descriptions and helps designers focus their attention on more complex issues. In one embodiment of the invention, this specification and confirmation of compatibility restrictions and configuration constraints is based on a mechanism which matches attribute values of the language elements to be connected. This mechanism is described in more detail below after a more detailed description of the architectural description language and the entity specialization mechanism.
One embodiment of an architectural description language in accordance with the present invention will now be described in connection with a representation of an example application using this language.
Activities and dependencies are connected together via ports which are connected at 82, 84, 86 and 88. Activity ports are connected to a corresponding dependency port using an object called a wire, drawn as line segments in the diagram. Within activity 74, ports connected at 90 and 92 connect the open database 94 and retrieve file name 96 activities via prerequisite dependency 98. Similarly, in activity 76, ports connected at 100 and 102 connect the start viewer 104 and view new file 106 activities via prerequisite dependency 108. The dependency has an associated resource not shown, which in this case is a file.
This example application illustrates four primary elements of the language, namely activities, dependencies, ports and resources. Any of these four elements may contain an arbitrary number of additional attributes. Attributes are name value pairs that encode additional information about the element. They are used to express compatibility restrictions that constrain the connection of elements. Each of the entities, or a specialization of it, has a corresponding implementation level entity that implements the intended functionality of the entity. These are defined as attributes of the respective activities, dependencies and ports and are called software components, coordination processes, software connectors, respectively. For resources, these attributes may represent data, control, hardware or system resources.
More details of this language will now be described in connection with
Activities are defined as sets of attributes which describe their core function and their capabilities to interconnect with the rest of the system. The two most important activity attributes are a decomposition and a component description. Decompositions are patterns of simpler activities and dependencies which implement the functionality intended by the composite activity. The ability to define activity decompositions is the primary abstraction mechanism in the language. A component description connects an activity with a code-level component which implements the intended functionality. Examples of code-level components include source code modules, executable programs, network servers, configuration files for enterprise systems, etc. Component descriptions are described in more detail below in connection with an example implementation.
Depending on the values of the decomposition attribute, an activity is either atomic or composite. Atomic activities have no decomposition. Composite activities are associated with a decomposition into patterns of activities and dependencies. Depending on the values of the component description attribute, an activity is either executable or generic. Executable activities are defined at a level precise enough to allow their translation into executable code. Activities are executable either if they are associated with a component description, or if they are composite and every element in their decomposition is executable. Activities which are not executable are called generic. To generate an executable implementation, all generic activities must be replaced by appropriate executable specializations. A primitive entity is both atomic and executable.
Activity decompositions are subject to structural restrictions. In particular, all free ports (described in more detail below) of activities contained in the decomposition, i.e., ports not connected to other decomposition elements, must be connected to compatible ports of the composite activity. In other words, the external points of interaction of a composite activity with the rest of the system are equal to the points of interaction of its decomposition, minus the interactions that are internal to the decomposition. Another restriction is that dependencies contained in an activity decomposition can have no free ports. In other words, if a dependency is included in a decomposition, all of its ports are connected to activities included in the same decomposition. Dependencies that span composite activities are defined outside of any of them because of the restriction that activities are connected to one another through intermediate dependencies.
As discussed above, executable activities are ultimately implemented by associating them with software components that perform the desired functionality. Software components are code-level software entities, such as source code modules, executable programs, user-interface functions, network services, etc. Dependencies and ports, on the other hand are associated with coordination processes and software connectors, respectively. While the latter may be more easily represented in this system, in order to properly integrate software components into executable systems, this representation should have some information about their interfaces, source and object files, and other related attributes. A notation, herein called a component description language (CDL) may be used to describe the properties of software components associated with executable activities. These definitions are stored in the corresponding executable activity.
One implementation of the component description language will now be described in connection with
Definitions of arbitrary kinds of software components, such as a source module, executable program, user-interface function, etc., may be supported by representing each component kind by a different keyword. Table I describes some example component kinds, and is not intended to be either exhaustive or limiting. This table could be extended, for example, by adding a component type for representing configuration files for enterprise software packages or workflow systems.
Component Type
CDL Keyword
Source procedure
A source code procedure or
equivalent sequential code block
(subroutine, function, etc.)
Source module
A source code module, consisting
of one or more source code files
and containing its own entry point
(main program). Modules interact
with the rest of the system through
expected interfaces only.
A source code procedure that reads
its inputs from and/or writes its
outputs to sequential byte streams
An executable program
DDE server
A DDE server embedded inside an
executable program
OLE server
An OLE server embedded inside an
executable program
A function provided by the
graphical user interface of some
executable program, typically
activated through a key sequence
The provided component interface, through which a software component interacts with other components, specifies the input-output interface of the component. Depending on the component kind, such interfaces might correspond to procedure parameter lists, executable program command line invocation interfaces, user interface functions activation key sequences, etc. When associating software components to executable activities, each element of the provided interface is mapped to a corresponding atomic port of the activity.
Expected interfaces of other components are also represented because most currently used software components make assumptions about the existence of other components or services in the system. For example, a source module might call an externally defined procedure with a specified name and parameter interface. A Microsoft Windows executable program might assume the existence of a DDE server application with given specifications. Such expectations are documented in this section, using a syntax identical to the one used to define the component's provided interface. When associating software components to executable activities, each element of each expected interface is mapped to a corresponding atomic activity port.
Files needed by a software component are usually pieces of code, residing in one or more source or object files. The relevant set of files to be eventually included in the final application are therefore specified.
Additional component attributes often need to be specified. Examples of such attributes include the programming language (for source components), the invocation pathname (for executable programs), the service and topic names (for a DDE server component), the activation, event or key sequence (for user-interface services), etc. There are also optional attributes, such as restrictions on the target environment or host machine.
As an example, referring now to
Activity Start Viewer 260 is associated with an executable program (Microsoft Word, a commercial text editor). Enactment of the activity corresponds, in this case, to invoking the program. The component's CDL provided interface 262 describes the command line parameters for starting the program. In this case there are no command line parameters, other than the program pathname.
Finally, activity View New File 264 is associated with a graphical-user-interface function offered by the text editor as indicated at 266. In order to display a new file, the text editor normally expects to receive a key sequence in its main window, consisting of the character CTRL-O, followed by the required filename, followed by a newline character. Thus, this service expects one abstract data resource (the filename), embedded in a key sequence whose generic format is described by attribute guiKeys. In this example, guiKeys contains the characters ^O(=CTRL-O), followed by @1(=the value of the first interface element, in this case the filename), followed by ˜(=newline). Finally, attribute guiWindow specifies the title of the editor's main window, where the activation key sequence must be sent.
Having now described activities in some detail, dependencies will now be described in connection with
In the example application in
Like activities, dependencies are defined as sets of attributes. One attribute is an optional decomposition into patterns of simpler dependencies that collectively specify the same relationship with the composite dependency. A second optional attribute is a coordination process. A coordination process is an activity, or a pattern of simpler dependencies and activities that describe a mechanism for managing the relationship or constraint implied by the dependency. Another attribute is an optional association with a software connector. Connectors are low-level mechanisms for interconnecting software components that are supported directly by programming languages and operating systems. An example software connector is the design-time ordering of program statements in the same sequential code block, which manages prerequisite dependencies. As another example, local variable transfer manages flow dependencies. Another example is a UNIX pipe protocol which is a form of transport of data from one process to another. Other examples include procedure calls, method invocations, shared memory, etc.
Depending on the values in the above attributes, a dependency may be either atomic or composite. Atomic dependencies have no decomposition. Composite dependencies are associated with patterns of simpler dependencies that specify the same relationships. A dependency also may be either managed or unmanaged. Managed dependencies have an associated coordination mechanism, specifying one way of managing the interconnection relationship they represent. Unmanaged dependencies have no associated coordination process. They simply specify the existence of a relationship and must be specialized by appropriate managed dependencies before code generation can take place. A dependency also may be executable or generic. Executable dependencies are defined at a level specific enough to be translated into executable code. Dependencies are executable if one or more of the following conditions hold: (1) they are directly associated with a code-level connector, (2) they are composite and all elements of their decomposition are executable, or (3) they are managed and all elements of their coordination process are executable.
Arbitrary dependency types may be defined. However, it is preferable to make routine the step of specifying and managing dependencies in the transformation of an architectural description into executable code. For that reason, it is useful to define a standardized vocabulary of common dependency types that covers a large percentage of activity relationships encountered in software systems. Such a vocabulary is described in more detail below. One common dependency is a prerequisite dependency, which requires a first activity to be completed before a second activity may start. A flow dependency represents a producer/consumer relationship between activities. A mutual exclusion dependency is a constraint often imposed for managing access to a shared resource.
Some dependencies can be equivalently described by patterns of simpler dependencies. Such patterns are called dependency decompositions and are defined as attributes of composite dependencies.
Dependencies specify interconnection relationships which translate into needs for interaction among a set of activities. To generate executable systems, dependencies must be managed by inserting appropriate interaction or coordination mechanisms into the system. By providing an abstraction for specifying a coordination process as an attribute of dependencies, the definition of such interaction mechanisms can be localized.
Coordination processes are patterns of simpler dependencies and activities. In that sense, they are very similar to activity decompositions. Coordination decompositions have ports defined by corresponding dependencies while activity decompositions have ports defined by corresponding activities. Accordingly, coordination processes have structural restrictions, which mirror the restrictions for activity decompositions, discussed above. In particular, all free ports of dependencies contained inside a coordination process, i.e., ports not connected to other elements of the coordination process, must be connected to compatible ports of the associated dependency. In other words, external points of interaction of a coordination process with the rest of the system are equal to the points of interaction of its elements, minus the interactions that are internal to the coordination process. In addition, activities contained inside a coordination process can have no free ports. If an activity is included in a coordination process, all of its ports must be connected to dependencies included in the same coordination process. Activities that span coordination processes must be defined outside of any of them. Dependencies are connected to one another through intermediate activities.
Having now described dependencies in some detail, the connectivity between activities and dependencies, herein called ports, will now be described in more detail in connection with
For example, in
As is the case with activities and dependencies, ports may be distinguished into composite and atomic ports. Composite ports act as abstract port specifications, describing the logical role of the port in the system. They decompose into sets of simpler ports, which might themselves be composite or atomic. Atomic ports map directly to an element of some implementation-level component interface, as will be described below. A user may define new ports as specializations of other types of ports, or define completely new port types, just as activities and dependencies may be defined.
A built-in port hierarchy implies that atomic ports are either input or output ports of data or control. Atomic data ports are mapped to atomic interface elements of software components or executable coordination processes. The mapping is performed by setting an attribute, e.g., "MapsTo," at the port to a string indicating the respective interface element. Depending on the component kind, an atomic port might thus correspond to a source procedure parameter, a command line argument, a user-interface-function activation key sequence, an event detected or generated by a program, an object generated or used by an executable program, etc. All atomic data ports contain an attribute named Resource, which lists the data type expected to flow through the port.
Atomic control ports, on the other hand, model the flow of control in and out of an activity or coordination process. Every activity has at least one pair of control ports modeling the beginning and end of execution of the activity. These ports are called the Begin and End ports. Complex activities might have additional control ports, modeling, for example, periodic calls to other activities that take place during the life of the original activity.
Sets of atomic ports may be grouped inside composite ports. Arbitrary port types may be defined. For example, producer and consumer ports specify the production and consumption of abstract resources. Designers might want to use composite ports for two reasons. First, they may be used to indicate sets of logically related interface elements in a given implementation. Second, they may be used to indicate generic needs of interaction when designing generic entities. Different specializations of a given generic entity might contain different decompositions of the same composite port, corresponding to the variety of interfaces by which a given abstract need for interaction can be implemented. An example of the use of composite ports will now be described in connection with
One of the activities in the File Viewer application makes the contents of a file available to the rest of the system. Initially in the design process, the exact implementation and interface of the component that will implement that activity is not known. Therefore, a generic activity 188 called Generate Input may be specified, as illustrated in
There are at least two ways to implement the Generate Input activity.
By default, every composite activity port includes the Begin and End ports of its associated activity in its decomposition. Activity ports are directly connected to coordination process ports. Coordination processes often need to control what happens before or after the execution of an activity. This requires them to have access to the Begin and End ports of an activity. In actual practice, this requirement is frequent enough that Begin and End ports are included in the decomposition of every composite activity port by default.
Having now described activities, dependencies and ports, another kind of entity, herein called a resource, will now be described in connection with
Such preexisting resources may be represented using a special resource language entity. Like activities, resource entities have ports, through which they are connected to the rest of the system. Atomic activity ports, are associated with interface elements of software components. In contrast, atomic resource ports are bound to constant data values, which usually correspond to resource identifiers.
All primary entities of the language, i.e., activities, dependencies, ports and resources, may contain an arbitrary number of additional attributes. Attributes are name-value pairs that encode additional information about the element. Attribute values can be scalar, lists, or pointers to other entities. Attributes are useful in determining compatibility of an entity with other entities in the system and for integrating components and coordination processes into sets of executable modules.
Although arbitrary attributes may be defined, some conventions for attributes used in each entity type have been developed. These conventions are represented in Table II. These conventions are intended to be neither exhaustive nor limiting.
Entity Type
Required Attributes
All Activities
execution environment(s)
for which activity is
Activities associated to
source programming
source module
language of module
name of executable
where module is to be
Activities associated with
pathname of
executable program
executable program
Activities associated with
Server DDE service
DDE server components
Server DDE topic name
Activities associated with
Format string of
graphical user interface
activation key sequence
function components
Name of window where
activation key sequence
should be sent
All atomic ports
pointer to interface
element corresponding
to port
type of data flowing
through port
All atomic ports MapsTo pointer to interface element corresponding to port Resource type of data flowing through port All entities inherit not only the decomposition but also all attributes from their specialization parents. In addition, language elements also inherit all attributes defined at their decomposition parents. These features enable attributes that are shared by all members of a composite element to be defined only once at the decomposition parent level. For example, in
In addition to normal values, attributes can be assigned to attribute variables. Attribute variables are strings that begin with "?". For example, the attribute Resource can be assigned the attribute variable "?res". Attribute variables need not be declared. They are automatically created the first time they are referenced. Unique variables are special attribute variables whose names begin with the string "?unq," e.g., ?unq-var, ?unq1, etc. They have the special requirement that their values cannot be equal to the value of any other variable in the same scope. They are used to express inequality constraints, as discussed in more detail below.
Attribute variables also are local to each owner entity, whether activity, dependency or resource, but are shared among an owner entity and all its ports. For example, all references to a variable at different ports of an activity refer to the same variable. Setting the variable at one of the ports affects both attribute definitions. Likewise, all references to a variable with the same variable name but at ports of second different activity refer to the same variable, only within the second activity. References across activities refer to different variables. For example, setting the variable at the first activity does not affect the value of a variable with the same name at the second activity.
The last entity of this architectural description language is called herein "wires," which are drawn as simple line segments to indicate that a legal connection has been established between a port of an activity and a port of a dependency. A wire also may be called a connector, but should not be confused with software connectors, relating to dependencies. Every time a new connection is attempted, the system performs a compatibility check, based on unification of corresponding attribute values at the two ends of the connection. Accordingly, establishment of a wire between composite ports implies that a set of legal connections between each of the corresponding subports has been made.
There are two types of wires in this system, internal wires and external wires. Internal wires connect free ports of decomposition or coordination process elements to compatible ports of their associated composite elements. For example, in
External wires connect activity ports to dependency ports. An activity port cannot be connected directly to another activity port. Similarly, a dependency port cannot be connected directly to another dependency port. Furthermore, the port at the activity side must be equal to or a specialization of the port at the dependency side. This restriction reflects the coordination perspective on software architecture adopted by this architectural description language, whereby software systems are represented as sets of activities interconnected through explicitly represented relationships. These restrictions on wires define the constraints that determine whether elements are compatible, and whether they can be connected by a designer who is generating an architectural description of a particular program.
Entity Specialization
Having now described the entities represented by this architectural description language, a property of inheritance used to implementation this language will now be described in more detail. Object-oriented languages provide the mechanism of inheritance to facilitate the incremental generation of new objects as specializations of existing ones, and also to help organize and relate similar object classes. An analogous mechanism may be used in the present invention to provide what is called herein, entity specialization. Entity specialization applies to all the elements of the language, and allows new activities, dependencies, ports and resources to be created as special cases of existing ones. Specialized entities inherit the decomposition and other attributes of their parents. They can differentiate themselves from their specialization parents by modifying their structure and attributes using editing operations described below. Entity specialization is based on the mechanism of process specialization described in Publication WO94/19742.
The mechanism of entity specialization enables the creation of specialization hierarchies for activities, dependencies, ports, resources and coordination processes. Such hierarchies are analogous to the class hierarchies of object-oriented systems. In specialization hierarchies, generic designs form the roots of specialization trees, consisting of increasingly specialized, but related designs. The leaves of specialization trees usually represent design elements that are specific enough to be translated into executable code. Specialization hierarchies have proven to be an excellent way to structure repositories of increasingly specialized design elements, such as a vocabulary of common dependency types, described in more detail below.
Apart from enabling the organization of related design elements into concise hierarchies, entity specialization also encourages application development by incremental refinement of generic application architectures. Designers can initially specify their applications using generic activities and dependencies. Such generic application architectures can then be iteratively refined by replacing their generic elements with increasingly specialized versions, until all elements of the architecture are executable. The existence of repositories of increasingly specialized design elements can reduce the specialization steps to a routine selection of appropriate repository elements.
Accordingly, in a way analogous to object-oriented class creation, entities in this architectural description language are created as specializations of other elements. New elements inherit the decomposition, coordination process, and all other attributes defined in their specialization parent. They can differentiate themselves from their parents by applying any number of the following transformations to their attributes, including either adding or deleting a decomposition or coordination process element, replacing a decomposition or coordination process element with one of its specializations, adding or deleting a connection, adding or deleting an attribute or modifying the value of an attribute.
Specializing activities allows incremental refinement of architectural diagrams. Designers can specify architectures in very generic terms and then incrementally specialize their elements until an executable design has been reached. Such a process is supported by the ability to maintain hierarchies of increasingly specialized activities, encoding families of alternative designs for specific parts of software architectures.
From a linguistic perspective, specialization and decomposition impose constraints to ensure compatibility of ports between decomposed or specialized entities are the entities to which their parents connect an activity can be replaced with a specialization only if the new specialization is able both to replace structurally the original activity and to connect legally to all neighbor elements connected to it. If the specialization is composite, the same requirements apply for its decomposition as well. The requirements translate into two port compatibility requirements. First, for each connected port of the original activity, there must be an equivalent port of the specialization. Second, each port of the specialization must be compatible with the dependency port to which the corresponding port of the original activity was connected. These port compatibility requirements are enforced in the process of editing such representations, to be described in more detail below.
Dependencies also may be specialized. In order to derive executable implementations from such abstract descriptions, designers can follow two alternative paths. First, if a generic dependency has a decomposition, all elements of the decomposition can be replaced with executable specializations. Alternatively, a generic dependency may be replaced with a managed specialization. Managed dependencies are associated with coordination processes, which represent interaction protocols.
From a linguistic perspective, a dependency can be replaced with a specialization only if the new specialization is able to structurally replace the original dependency and legally connect to all neighbor elements connected to it. If the specialization is managed, the same requirements apply for its coordination process as well. The requirements translate into two port compatibility requirements similar to the ones for specializing activities. First, for each connected port of the original dependency, there must be an equivalent port of the specialization. Second, for each port of the specialization must be compatible with the activity port to which the corresponding port of the original dependency was connected.
Entities inherit attributes from their specialization parents. In addition, entities may "inherit" attributes from their decomposition parent as well. This features allows an attribute which is shared by all entities of a process to be defined once at the top-level activity and then be automatically inherited by all members of the decomposition. For example, suppose we have an attribute 'Company Name'. In a model of a process performed entirely by a single entity, the 'Company Name' may be defined once at the parent level. All subactivities of the process automatically inherit that attribute. This capability not only saves the need to manually enter 'Company Name' into all subactivities, but also allows some generic activities to be included unchanged in the decomposition, without the need to create different specializations of them, one for each different decomposition context in which they might be used.
Dependencies optionally may have associated coordination processes. The association is simply encoded by defining an attribute 'Coordination Process' at all dependencies and setting that attribute to point to the associated coordination process. Coordination processes must be able to structurally replace their associated dependencies in a given model. Therefore, coordination processes must be port compatible with their associated dependencies. In other words, for every port of a dependency, there must be a port of the coordination process which is equal to or a specialization of the corresponding dependency port.
One way to ensure port compatibility of coordination processes is by implementing the coordination process as a set of two siblings. One sibling is defined directly under the associated dependency and the other sibling is defined as an activity. The dependency sibling inherits the port structure of the associated dependency, while the activity sibling contains information about the patterns of activities and dependencies that form the decomposition of the coordination process. The connections between decomposition elements of the coordination process and the external ports of the coordination process are also stored in the dependency sibling. In that way, the system ensures that coordination processes are port compatible with their associated dependencies, because, in a way, they are defined as specializations of a dependency entity. The separation of information about decomposition and external port structure into two siblings also allows the same coordination process, i.e., the activity sibling, to be associated with several different dependencies. Coordination processes also may be implemented as a specialization of activities and can be provided with a separate port compatibility checking process that matches its ports with those of its included dependencies.
Implementation of Process Representation
Having now described the general entities of the language and the restrictions on their combinations, the representation of a process or software architecture in a computer system will now be described in connection with
Entities may be represented using many kinds of data structures in a computer program. In the following description we provide equivalent representations of the structures as objects or as relational database tables. Entities may be represented as classes in an object-oriented database or development environment. One development environment is KAPPA-PC development tool, from Intellicorp, Inc., but any other object-oriented system or database which provides the ability to define new subclasses dynamically at run-time can be used. Using the KAPPA-PC development tool, specialization is simply implemented using the properties of object-oriented inheritance. Specialization children are defined as subclasses of existing classes, and thus they automatically inherit all slots which are present in their parent. Multiple inheritance is supported by storing entities with multiple parents as a set of sibling classes. A different sibling class is defined under each specialization parent. Each sibling inherits all slots from its respective parent. Appropriate software coordinates the handling of siblings and combines decomposition and attribute elements inherited by each sibling.
Entities also may be represented using relational database schema. In the following description, the data structures may be implemented using relational database tables, where the fields in a particular structure are records in a table defined by the illustrated structure. In this implementation, of course, inheritance is implemented by appropriate software that provides similar functionality as the object-oriented development system. The following description does not give an exhaustive list of records for each table, or slots for each object, but only lists the relevant fields that convey the essentials of the implementation.
The primary kinds of entity, i.e., activities, dependencies, ports, and resources are all defined as specializations of the class PHObject 110, such as shown in
These four entity kinds share the following properties: they have a name, they are defined as a specialization of one or more entities, and they inherit a decomposition and attributes from a specialization parent. Differences among entity kinds are captured in semantic rules that specify what entities are allowed to be present in a decomposition, specific attributes that are always present in certain entity kinds, etc. It is also possible to provide another type of entity in the representation, called a "bundle," to group together related specializations of a given parent entity. Bundles are used in a Process Handbook representation to control automatic inheritance of properties by specializations of a parent entity. This representation makes it easy to add yet other entity kinds, e.g., actors, which may actually perform a particular activity, or send or receive, information etc.
Specialization is represented by a parent object or table 120 as shown in
An entity also may have a decomposition, which is defined as a set of decomposition slots. A decomposition slot may be, for example, a pointer to an entity contained in the decomposition. Alternatively, a decomposition slot may be a pointer to a connector entity, which is a secondary entity that represents connections among primary entities present in the decomposition. In other words, a decomposition generally indicates a list of other entities and a list of connections among those entities. The rules for what kinds of entities and what kinds of connections are allowed in a decomposition depend on the entity kind as discussed above. In addition, all entities can have an arbitrary number of attributes. Decomposition slots may be stored as part of the entity class in an object-oriented system. In a relational table implementation, decomposition slots may be stored in a separate table. A table 130 for a decomposition is shown in
A slot identifier is used to handle, for example, the case where an activity A contains two subactivities B and C in its decomposition. The decomposition thus contains two "slots", e.g., S1 and S2, which are "filled" with activities B and C respectively. If an activity A′ is defined as a specialization of activity A, new activity A′ inherits all decomposition slots and their values from activity A. In activity A′, however subactivity B is replaced with subactivity B′. By using a separate "slot" id, the replacement is made by modifying the slot value for slot SI from the identifier for subactivity B to the identifier for subactivity B′. In addition to allowing simple replacements, this scheme also permits the system to represent the fact that B′ is a replacement of a previously inherited element.
Another structure called a connector, corresponding to the wire entity, is used to connect elements together. Connectors are displayed as lines linking ports of one entity to ports of another entity. As shown in
Basing connectors on lists of slot identifiers, as opposed to lists of successive decomposition object identifiers, has the following advantages. First, the sequence of slot identifiers is traversed to reach a particular endpoint which allows connectors between different instances of the same entity to be defined unambiguously. Second, connectors may be inherited from a parent and remain unaltered after one of more connected activities are replaced by some of their specializations in the child. In other words, specializations may be modified without worrying about connectors.
Attributes of an entity also may be represented as additional fields of the entity, and may have arbitrary attributes. Attributes have a name, a type, a value, and possibly links to additional information. Example attribute types include scalar values, e.g., numeric, boolean or string, pointers to other Synthesis objects, pointers to system objects, e.g., files or OLE objects, and lists. Attributes optionally may be given a variable as a value. Variables are used to check port compatibility when establishing connections or when replacing entities with specializations, as will be described in more detail below.
Having now described an architectural description language in accordance with the invention, and one implementation of a representation of architectural descriptions, various systems for using this process representation will now be described.
There are various user-interface clients that can be provided to read the process descriptions stored in the process repository to generate appropriate displays to users as illustrated above in connection with
Another particularly useful tool is an editor 42 which allows a user to graphically input representations of a software system. Such a system may be provided using several kinds of interfaces, but may use a graphical system such as VISIO, a commercial application for drawing charts and diagrams from Shapeware Corporation. VISIO can act as a graphic server for other applications through a windows protocol called OLE Automation which allows an application to act as a globally accessible application offering a set of methods to other applications. The implementation of a suitable user interface and the provision of editing functions and entity specialization may be performed using systems such as shown in the PCT Publication WO94/19742 and in the U.S. Provisional Application Ser. No. 60/013,694 which is incorporated by reference.
Checking Element Compatibility
In the editor for this system, when a dependency is connected to an activity a compatibility check is done between the ports of the activity and the ports of the dependency. Such a connection occurs when a new activity or dependency is added to the representation, or when an activity or dependency is modified or replaced. This process will now be described briefly.
As discussed above, there are several semantic restrictions and constraints on the ability of entities to interconnect. Some of these restrictions are encoded in the syntax of the language. For example, activity ports can be connected only to dependency ports. Furthermore, dependency ports can be connected only to activity ports that are equal to or a specialization of them.
Other restrictions are specific to the attributes of code-level elements, i.e., components and connectors, associated with executable activities and dependencies. One such restriction is that an activity associated with a source code procedure returning an integer value can only be connected to other activities through dependencies associated with coordination processes capable of transporting integer values. Another such restriction is that flow dependencies managed by local variable connectors can only connect activities whose associated components can be packaged inside the same sequential code block. Similarly, flow dependencies managed by, for example, a DDE transfer coordination process, can connect only with activities whose associated components are packaged in different executables within the same Microsoft Windows-based host.
These restrictions and constraints are encoded so that a number of compatibility tests can be performed automatically by the language. Hence, a problem similar to type checking in a programming language arises whenever two elements are connected together. Since all connections are between ports, it is desirable to be able to perform compatibility checks at the port level, and when a wire is to be established between two ports.
Compatibility checking may be based on attributes which specify the compatibility restrictions. Before establishing a connection between two ports, a port matching algorithm that determines port compatibility is performed, as will now be described in more detail in connection with
The semantics and scope rules of attributes and variables discussed above permit a number of compatibility constraints to be encoded into attributes. For example, if an attribute must have a specific value at all neighbor elements, the attribute may be defined with the specified value at all ports where this condition is required. If the condition is required at all ports of an owner element, the attribute need only be defined once at the owner element. For example, a dependency managed by a coordination process encoding a UNIX pipe protocol can be used only to connect components that will run in UNIX environments. Designers can encode this constraint by defining an attribute Environment set to UNIX at the top level of the process. This attribute is inherited by all ports. In order to pass the compatibility check, all connected activities must contain the attribute set to the same value.
As another example, if an attribute must have the same unspecified value at all neighbor elements, the attribute may be set to the same variable name at all ports where this condition is required. The unification process will only succeed if the equivalent attribute at the other end of all connections has the same value. For example, local variable transfer is the simplest coordination process for managing flow dependencies. However, it can only be used if all its members both produce and use the same data type, and can be packaged into the same procedure. The latter requirement implies that they also have to be written in the same language and be packaged into the same executable program. For example, as shown in
As another example, if an attribute must have a different value at each neighbor element, the attribute may be set to a different unique variable at each port where this condition is required. Since each unique variable cannot be unified to a value given to any other variable, unification will only succeed if the attribute has a different value at each neighbor element. For example, Dynamic Data Exchange (DDE) is one protocol for transferring data among different executable programs in the Microsoft Windows operating system. It does not work properly for transferring data within the same executable. Thus, it can only connect components that will be integrated into different executables. For example, as shown in
Attribute unification simultaneously checks constraint compliance and creates equivalence classes of attribute values across a number of elements. For example, an attempt to connect two activities through a dependency managed by a local variable transfer coordination process (
The process of checking compatibility of activity and dependency ports is illustrated in more detail in
The comparison of the attributes is performed by calling a Match Value function when both ends have a value as indicated at 468. If one end has a value and the other end refers to a variable and if this variable has a value, then the Match Value function 468 is also called. If one end refers to a variable and the variable does not have a value, both this variable and its equivalents class are set to the value at the other end of the matching port in step 472 and success is indicated as in step 470. If both ends refer to variables and if one or both variables has a value, then the steps, as indicated at 472, are again performed. If no variable has a value then the process proceeds with step 474 of unifying both variables into an equivalence class and returning success.
The Match Values procedure takes the value of an attribute at the activity side and a value of an attribute at the dependency side and returns success when the values match and failure otherwise. In particular, if the values are pointers to language elements and if the attribute at the activity side is a specialization of the attribute at the dependency side, success is returned as indicated at 476.
Constructing Representations of Software Architectures
Given the linguistic support for defining and checking architectural diagrams, described above, and design support for leveraging the construction of correct diagrams, application architectures may be easily constructed using an editor. In particular, the architectural description language described above supports a set of graphical abstractions as shown in
Apart from linguistic support for specifying activities and dependencies, the construction of application architecture diagrams can be facilitated by assistance on how to decompose an application to simpler functional pieces, and assistance on how to represent interdependencies among application functional pieces.
Application decomposition can be facilitated by the reuse of generic decompositions for frequently occurring problems. This requires the creation of process repositories, or process handbooks, for storing, searching, and reusing architectural design fragments. The architectural description language provides a number of mechanisms for supporting the construction of process repositories. Architectural patterns can be expressed as composite activities. Through the mechanism of entity specialization, sets of related composite activities can be organized and stored in a specialization hierarchy. Specialization hierarchies are similar to class hierarchies in object-oriented system, and can be used as the basis for structuring repositories of reusable architectural patterns.
The problem of specifying interdependency patterns among application activities can be similarly facilitated by a repository of dependency types for frequently occurring patterns of interaction. Because interconnection relationships can be described using a relatively narrow set of concepts, orthogonal to the problem domain of most applications, a standardized, but extensible, vocabulary of dependency types, can be used by designers to express the interaction requirements in their applications. The specialization mechanism of the architectural description language can be used to store and structure the vocabulary of dependencies. Such a repository may be considered as a design handbook of representations of coordination processes for managing dependencies of a variety of types. The design handbook may be used to review several instances of different types of coordination processes for managing types of dependencies.
Implementation of an example entity repository is described in more detail below. The entity repository may have a browser allowing for tree-like views into the hierarchies of the defined coordination processes. The browser may be implemented following the teachings of PCT Publication No. 94/19742. An implementation of a design handbook of coordination processes will now be described.
Repository of Coordination Processes
In the design handbook, the different kinds of dependencies in software systems define a design space which maps each type of dependency to a family of alternative coordination processes for managing it. A particular coordination process is selected from that family by specifying the values of a relatively small number of additional parameters called design dimensions. For example, a coordination process for managing a data flow dependency can be selected by specifying the type of carrier resource, e.g., shared memory, file, or pipe, and the paradigm, e.g., push, pull, peer or hierarchy, for managing the embedded prerequisite. Some of the alternatives can be automatically ruled out by compatibility constraints. For example, when designing a data flow between two components running under UNIX, only data transport mechanisms supported by UNIX can be considered as alternatives. This reduces the selection of a coordination process to a routine selection of a relatively small number of design parameters.
Generally speaking, the design handbook correlates a vocabulary of dependency types into a design space of coordination processes. Dependencies generally encode the need of an activity to interact with other activities, either because they use resources produced by other activities, or because they share resources with other activities. As a result, there generally are flow dependencies between producers and consumers, resource sharing dependencies among consumers of the same resource and timing dependencies which specify constraints on the relative timing of two or more activities.
The design dimensions represented in
Specialization of flow dependencies based on resource kind translates into types of useability dependencies. These dependencies represent the simple fact that resource user should be able to properly use produced resources. Similarly, accessibility dependencies specify that a resource must be accessible to a user before it can be used. Such accessibility dependencies may be represented as resource kind dependencies or prerequisite dependencies, or as sharing dependencies.
Prerequisite kinds of dependencies specify that a resource must be produced before it can be used. As indicated in
Sharing dependencies arise when more than one activity requires access to the same resource. Sharing dependencies arise in different variations on the number of producers, number of users, and whether it involves resource sharing or consumer sharing. Resource sharing considerations arise in one-to-many flow dependencies because more than one activity uses the same resource. Consumer sharing dependencies arise in many-to-one flow dependencies because more than one producer produces for the same consumer activity. Sharing resources may have coordination requirements depending on the divisibility, consumability, or concurrency capabilities of the resource. Several example processes for managing these various types of dependencies are illustrated in U.S. Provisional Application Ser. No. 60/013,694, filed Mar. 19, 1996.
Considering timing dependencies shown in
Another category of timing dependency is the overlap dependency which specifies that a first activity can only begin execution after a second activity is already in process. Such relationships typically imply resource relationships between the first and second activities. One subcategory of this kinds of dependency is the "during" dependency which specifies that a first activity can only execute during this execution of a second activity. As an example, a network client can only execute successfully during execution of the system's network driver. A starts dependency specifies that a first activity must start execution whenever a second activity starts execution. As an example, a printer driver is often initialized at the same time a word processor program is started. A particular form of this dependency is the simultaneity which specifies that all activities in a set must start execution at the same time. These dependencies can be transformed into many-to-many prerequisite dependencies and managed as such.
Another kind of timing dependency is a finishes dependency which specifies that the completion of a first activity also causes a second activity to terminate. This dependency is most often used to specify application termination relationships. A particular specialization of this dependency is the simultaneous end dependency which specifies that all activities in a set must terminate if any of them completes execution. As can be seen, many of these timing dependencies can be represented by prerequisite flow dependencies, and can be managed as such.
More complex composite dependencies can be represented to indicate arbitrary static flow patterns, multiple unit directional flows, exchange dependencies, circular flows, etc. Each of these dependencies has corresponding coordination processes associated therewith. Each of the design dimensions specifies a different dependency type for which there may be several coordination processes. These coordination processes have characteristics which define coordination design dimensions within a particular dependency type. Each point in the coordination design space defines a different coordination process. There are many other ways to represent the design dimensions for coordination processes. Accordingly, the foregoing is neither exhaustive nor limiting of the present invention.
Automatic Generation of Executable Code from Software Architecture Descriptions
Given a description of a software system using the above-described architectural description language, executable program code may be generated by transforming a software architecture definition according to a process which will now be described in connection with
As discussed above, activities can be generic or executable, which enables designers to specify the architecture of their applications at any desired level of abstraction. However, in order for executable code to be generated, all generic activities must first be replaced by executable specializations. Executable atomic activities, or primitive activities, are associated with some code-level software component, such as a source code module, or an executable program. Composite executable activities decompose into sets of executable elements. Therefore, the step of replacing generic activities results in the eventual association of all activities in an architectural diagram with sets of code-level software components.
The responsibility for locating and selecting the most appropriate code-level components for a designer. There are some proposed technologies for collecting software components into component libraries, easily accessible to the community of designers. Furthermore, new technologies, such as the Internet, are making a growing number of software component repositories readily accessible to designers. Once a component is selected, it may be added to the representation by providing a component description for the selected component.
Nonetheless, component selection is facilitated because each activity can be associated to a software component independently of any other activity. Also, designers do not have to worry about the specific form of components and their interfaces. Handling of potential mismatches between component interfaces is completely contained in the coordination processes that manage dependencies among components. With the present invention, designers need only care about whether a given component contains the functionality required by its associated activity and not about how it will fit together with other components already selected.
Similarly, in order to generate an executable system, generic dependencies must be replaced by executable specializations. Executable dependencies are either directly associated with a software connector, implementing a low-level interconnection mechanism, or with a coordination process, defined as a pattern of simpler dependencies and activities. In order to specialize the dependencies, linguistic support is needed to provide adequate abstractions for defining dependencies and design support, such as a process repository, should be provided to assist designers in selecting a software connector or coordination process that manages a given dependency, as described above.
The architectural description language described above provides the linguistic support by representing coordination processes and software connectors as attributes of dependencies. Coordination processes provide a single location for specifying all the pieces of an interaction protocol. In contrast, traditional programming languages usually force the description of interaction protocols to be distributed among the interacting components. The design support provided for assisting the selection of coordination processes is the design space of coordination processes for each element of a vocabulary of dependencies, described above.
Most of the coordination processes in the design handbook are defined at the generic level. This means that they are defined as sets of lower-level generic activities and unmanaged dependencies. For example, the generic process for managing a one-to-one data flow dependency consists of two lower-level generic activities and a number of unmanaged flow dependencies. In order to integrate that process in an executable application, each of those generic decomposition elements has to be specialized in turn. Therefore, the previous candidate selection process has to be recursively applied to all decomposition elements as well. The design process completes when all activities and dependencies introduced are executable. Executable activities have associations with code-level software components. Executable dependencies are associated to code-level software connectors, directly supported by specific programming language or operating system mechanisms, e.g., C procedure calls or UNIX pipe protocols.
This design process can be greatly assisted, or even automated, by computer. Assuming that there is an on-line repository of increasingly specialized dependency types, a generic dependency defined in the architectural description of a system is managed as follows.
A design assistant automatically searches the repository of managed specializations of the generic dependency. It rules out dependencies whose associated coordination processes are rejected by the compatibility checking process described above in connection with
The process of managing a dependency can be fully automated by allowing designers to specify evaluation functions, or constraints, that enable the computer to automatically rank candidate alternatives for each transformation. Such evaluation functions could be constraints on specific process attributes. For example, one constraint may be that all coordination processes must adhere to client/server organizations. Evaluation functions also may be related to the computational cost of coordination processes. Evaluation functions can further restrict the number of candidate coordination processes presented to designers. In some cases, they might restrict the candidates to one, in which case the selection process becomes fully automatic.
Since the process relies on the existence of a repository of coordination processes, there might be situations for which no compatible coordination process has been stored in the repository. For example, when managing a usability dependency which requires conversion of strings to integers in Visual Basic, there might be no such specialization of the conversion activity in the repository. In such cases, the system asks the users to define a new activity specialization with that functionality. The specialization typically does not require more than a few lines of code, and becomes a permanent part of the repository. In that manner, repositories of design elements can be incrementally extended and eventually become rich enough to be able to handle a large number of practical cases.
Such a process of selecting coordination processes relies on the assumption that every dependency can be managed independently of every other dependency, unless the designer has explicitly combined a number of dependencies into a composite dependency pattern. This assumption is equivalent to the assumption that the connections of an activity port to other parts of the application can be managed independently of the connections of every other port of the same activity. However, software components built with current technologies contain interface dependencies among their interface elements which, unless properly decoupled, would force connections of sets of activity ports to be jointly managed.
For example,
Managing dependencies independently of one another requires that their coordination processes do not share any code. Therefore, in
For similar reasons, in this example dependencies Flow 2 and Flow 3 must be jointly managed. Finally, all four dependencies in the diagram have to be treated jointly, in order to manage them properly. In addition to requiring additional mechanisms for automatically detecting such implementation-dependent "dependencies among dependencies," the existence of such dependencies could require explicit support for arbitrarily complex composite dependency patterns in a design handbook repository.
Such interface dependencies are related to the shortcomings of current-technology code-level components in separating interconnection assumptions from the implementation of a component's core functionality. They are intrinsic properties of the code-level components chosen to implement atomic activities. For that reason, they should be handled at a level orthogonal to that of managing dependencies among activities.
One way to handle interface dependencies is by introducing additional activities that attempt to decouple them. In other words, before attempting to manage any dependency, primitive activities are scanned and interface dependencies among their ports are detected. Whenever such dependencies are found, the original primitive activity is replaced with a composite augmented activity which includes activities for decoupling ports from one another, allowing them to be independently managed.
Interface dependencies may be detected because they are inherent properties of specific interface types. CDL definitions associated with every primitive activity contain information about the component's provided interfaces, as well as other interfaces expected by the component. Interface definitions involve a set of input and output data elements, e.g., "proc foo(in a:Integer, out b:String);". Each of those elements is mapped to a corresponding atomic port of the primitive activity. Interface elements are dependent on one another because they typically have to be combined together into a single interface call, e.g., a procedure call, or a single interface header, e.g., a procedure header.
One way to decouple interface dependencies is by transforming complex interfaces to and from sets of local variables. Each local variable stores one interface element. Since local variables can be independently read or written, this set of transformations enables each input resource to be independently produced and each output resource to be independently consumed.
The transformations require the introduction of two sets of mediator activities around primitive activities with interface dependencies, callers and wrappers. Callers are activities that read or write a set of independent local variables and construct a corresponding call to a given composite interface. Wrappers are activities that make a given composite interface available to the application, and demultiplex its elements into sets of independent local variables.
Using callers and wrappers, the process of decoupling interface dependencies among activity ports can be expressed as follows. Each primitive activity with interface dependencies is structurally replaced with an augmented activity which, in addition to the original activity, contains mediator activities including a caller activity for each interface provided by the component and a wrapper activity for each interface expected by the component. The caller activity connects to all ports originally associated with the provided interface of the component.
For example, as shown in
Since a caller activity connects to all ports originally associated with the provided interface of the component, it allows each dependency originally connected to the activity to independently read/write its associated resource to/from a local variable. The caller activity is then responsible for assembling all resources into the appropriate interface call.
In the same manner, wrapper activities connect to all ports originally associated with each expected interface. Wrapper activities define headers of composite interfaces called by other components. In addition, they store each element contained in those headers to independent local variables.
Callers and wrappers are specified per interface type. In fact, in order to support a new component kind, designers specify appropriate caller and wrapper activities for its associated interface type.
An example will demonstrate how callers and wrappers can be defined for a number of common interface types. If a component provides a source procedure interface, it can be invoked from inside other blocks of code by simple procedure calls. The default semantics of procedure calls enable them to receive their input parameters, and leave their output parameters to sets of independent variables. For example, in the C language call statement, "foo(a, b);", a and b are local variables that can be given values by independent statements preceding the call. As a consequence, provided procedure interfaces need not be augmented.
If a component expects a source procedure interface, this means that there is a call to a procedure, defined externally to the component, with the expected interface from within the code of the component. Therefore, a procedure definition with the expected name and parameter list must exist in the final application, and the code of this procedure must allow each element of its parameter list to be independently accessed by each activity connected to the corresponding atomic port of the calling component.
Such components are augmented by the introduction of procedure wrapper activities. Procedure wrappers translate to source code headers of procedure calls with the specified name and parameter list. Activities originally connected to the ports of an expected procedure interface, will be connected to the wrapper after augmentation takes place. For example, in
As another example, components that provide executable program interfaces correspond to executable program files. Caller activities for executable components are source code procedures which independently receive all command line parameters necessary to invoke the executable and construct the appropriate operating system invocation call, as shown in
If a component expects an executable program interface, this means that an executable program with the expected name and interface is invoked from within the code of the component. Such components are augmented by the introduction of executable wrapper activities. Executable wrapper activities translate to main procedure headers for executable programs with the expected name and parameter list. In addition, they introduce system-specific activities which read the command line argument structure passed to the main procedure by the operating system, and leave each passed argument to a different local variable. Activities originally connected to the ports of an expected executable interface, will be connected to the wrapper after augmentation takes place, as shown in
Finally, some programs designed for interactive use activate certain functions when users press a key sequence. For example, a text editor opens a file when users press CTRL-O, followed by the filename, followed by newline. In order to integrate such programs into larger applications, we view them as components that provide a special kind of interface, called a graphical-user-interface-function, or "GUI function". GUI-functions specify lists of input parameters, like any other interface. They also specify a format string, to which input parameters will be embedded in order to form the activation key sequence, and a window name, to which the activation key sequence should be send in order to activate the desired function.
Caller activities for GUI functions are source code procedures which receive the target window name, the format string, and all input parameters, and use operating system calls in order to send the activation key sequence to the target window, as shown in
There is one special case where the explicit introduction of caller and wrapper activities might lead to inefficiencies, or even errors. That is when two of more components with perfectly matching composite interfaces are connected to each other. In such cases, the composite pattern of dependencies that specifies the connections among those interface elements is automatically managed. In order to complete the support for this step, design assistants should first check for this special case.
Once generic design elements are specialized and interface dependencies are decoupled, executable code may be generated. As can now be seen, the "raw material" of this component-based application development process is a set of code-level software components, in source or executable form. The end product is also a set of code-level components, including the original components plus some additional modules containing the coordination software that manages interdependencies among the original components. The distinction between activities and dependencies leads to a very useful intermediate representation, which facilitates the design of the coordination software. Eventually, however, the original components plus the new activities and dependencies introduced by the process of design, are integrated into sets of source or executable modules. This transformation step will be described generally, and in more detail below. This transformation step can be completely automated.
When all elements of the diagram have been replaced by an executable specialization, executable activities have direct associations with code-level software components, such as source or executable code modules. Executable dependencies are associated with built-in language and operating system interconnection processes. For example, they may include sequentialization processes for managing prerequisite dependencies, which have coordination mechanisms that specify that the activities at their endpoints will be packaged inside the same sequential code block and that the precedent activities will always be placed before the consequent activities inside that code block.
An executable dependency may include local variable transfer processes for managing data flow dependencies. Local variable coordination mechanisms have the same semantics as sequentialization processes. In addition, they specify that a data item is being transferred from the precedents to the consequents through some automatically named local variable.
Other built-in language or operating system interconnection mechanisms, such as remote procedure calls, etc., also may be included. These processes are automatically provided by the infrastructure of the target configuration and do not translate into tangible coordination code. Therefore, these primitive coordination processes need not be addressed by this transformation.
Sequentialization processes and local variable coordination processes divide a graph representing the application into a set of partially ordered subgraphs of activities. Each subgraph contains activities to be packaged into the same sequential code module. In order to generate an executable system from this graph, the graph is translated into a set of modules in one or more programming languages. The translation process has two steps, namely connecting all sequential modules to control and generating executable code.
All sequential modules are connected to control because, in order to begin execution, every software module must receive control from somewhere. This is an application-independent requirement, analogous to the requirement that, in addition to their configuration-specific interconnections, all electronic components of a computer system must also be plugged into the power network.
The application diagrams specify application-specific constraints among activities, expressed by flow and timing dependencies, in a more or less declarative fashion. Activity control ports are connected to dependencies only if the execution of those activities depends on other activities. To avoid the cluttering of diagrams with unnecessary connectors, the system enables designers to leave unconnected control ports of activities that do not depend on any other activities. The default semantics for such unconnected control ports are that the respective activities should be started as early as possible during an application run. For example, in the File Viewer example application shown in
By allowing the existence of unconnected control ports, even after all dependencies have been managed some of the original and newly introduced modules might not be connected to a source of control. By default, these modules should start immediately upon initiation of the application. Therefore, before code can be generated, those modules have to be identified and connected by control flow dependencies to a source of control. Furthermore, in order to make the invocation of the application as simple as possible, all application modules are connected by control flows to a single application entry point, which is typically a user-selectable executable file.
One possible packaging strategy that achieves those goals is the following. First, the application graph is scanned to locate all source modules that are not connected to a source of control. A set of packaging executable components can be introduced, one per host machine and per language for which unconnected source modules exist. Calls to unconnected source modules are packaged inside the main program of the packaging executable corresponding to the host machine and language of each module. These steps introduce additional executable modules into the system. These executable modules must, in turn, be connected to a source of control, so that they can begin execution when the application starts. Accordingly, all executable programs that are not connected to a source of control are then located. An application entry executable component is then introduced into the system. This last component is the entry point to the entire application, and can be written in an operating system script language, or in any other programming language. Invocation statements for all unconnected executables can then be packaged inside the main program of the application entry executable.
This process of adding sources of control to the application introduces a set of additional activities and coordination processes into the application graph, as shown in
After this packaging has been completed, the architectural description graphs can be translated to sets of modules by a relatively straightforward process. Primitive coordination processes divide the graphs into families of partially ordered subgraphs, each corresponding to a sequential code block. Nodes in these subgraphs correspond to source code activities, that is, activities that are associated with source code procedures. Arcs in the graphs correspond to sequentialization processes and local variable primitive coordination processes that impose ordering constraints and data transfers through local variables.
The code generation process creates a topological sort of each subgraph, also handling the possibility of loops and branches, generates a procedure call statement for each activity in the subgraph, generates and automatically names local variables that transfer data among procedure call statements in the same subgraph, and packages all statements and variable definitions into sequential code blocks for the given language.
In order for the code generator to generate the correct syntax for each source language, the code generator has some language-specific knowledge for each language it handles. However, this language-specific knowledge may be quite limited, and can include syntactic rules for generating procedure calls, declaring local variables, and generating procedure headers and footers. Support for a new language can thus easily be concentrated into a single class definition. Providing support for a new language will be described in more detail below.
A more detailed description of the process of code generation will now be provided in connection with the flowcharts and pseudocode of
The process of decoupling interface dependencies will now be described in connection with
Referring now to
This specialization process will now be described in more detail in connection with
For each unmanaged dependency, for each coordination process associated with a specialization of the dependency and stored in the design repository, the compatibility checking algorithm is applied in step 410. If two (or more) matching coordination processes are found, the user is asked to select between them in step 412 unless information is available to permit automatic selection. If one matching coordination process is found, it is simply selected. If no matching coordination process is found, a user is asked to provide a compatible coordination process in step 414. This process is used if valid. Validity is checked in step 416 by applying the compatibility checking algorithm of
Referring now to
The generation of executable code will now be described in connection with
Example applications generated by this procedure are illustrated in U.S. provision patent application Ser. No. 60/013,694, filed Mar. 19, 1996, which is hereby incorporated by reference.
This architectural description language also may be used to automatically configure enterprise-wide software application packages, which are integrated software packages which attempt to support all the different business functions of an enterprise. The idea is that a company can purchase such a package, customize it to a certain extent in order to match its particular requirements, and install it instead of building its own software from scratch. Such packages are available from, for example, SAP, Oracle, Peoplesoft, and Baan. Most enterprise-wide software packages contain a number of configuration tables that can be modified in order to customize their operation.
A company interested in installing one of those packages typically starts by examining the current state of its business processes. It then needs to compare its processes with the set of alternative processes supported by the package. In most cases, the company would have to select the supported process that comes closest to its requirements and then change its current process to match the supported process. The package also may have to be customized to support the specific process variation that was selected.
The configuration of such enterprise-wide software applications can be facilitated, and in some cases completely automated, by associating configuration table information to every different process element that can be supported by the software package. All different process 54 variants supported by the software package can be stored and organized in a specialization hierarchy using the present invention. When users select one particular set of process variants that most closely correspond to the way their organization works, the resulting process model can be processed to generate the software package configuration tables.
In particular, in order to generate the configuration tables, the decomposition graph of the final process model is traversed. Each node in the graph is an elementary process supported by the software package. Associated with each elementary process are a number of configuration parameters stored in the form of attributes. As the graph is traversed, the configuration parameters found in the different nodes are collected and separated into groups corresponding to each configuration table. When the traversal is complete, the system simply builds the configuration tables based on the parameters it has collected.
Two situations might arise which complicate this process. First, two or more process steps selected in the final process model might specify conflicting values for one or more configuration parameters. In such cases, the user is notified, the conflicting process steps are identified and compatible alternatives may be presented. These alternatives may be identified by searching the specialization hierarchy for each conflicting process step in parallel, by examining their neighboring specializations, cousins, etc., and by identifying sets of process steps that both are compatible specializations of their corresponding conflicting process step and result in configuration parameter settings that do not conflict. This search step is very similar to the search of the coordination process space, performed by the design assistant in order to locate compatible coordination processes for a given dependency. If several compatible alternatives are located, the user makes the final selection.
Second, even after all process steps have been traversed, some essential configuration parameters might remain undefined. In those cases, a high-level description of the missing parameters may be presented to the user. Assistance may be provided through various help sequences to guide the user into providing values for these parameters.
Apart from facilitating the development of software applications by combining existing software components, this language and its associated tools have the potential to assist the development of new applications from scratch. In such an application, an editor 42 (see
Once designers have finalized the decomposition of an application into patterns of activities and dependencies, atomic activities are manually implemented. If the decomposition is sufficiently detailed, atomic activities are defined at a granularity fine enough to allow for a straightforward implementation. The design assistant 48 can assist the selection of coordination processes for managing dependencies through the process described above. When this step is complete, the code and/or configuration generator 44 can automatically generate coordination code, package components into procedures and executables, and produce a final executable system.
The development of systems using this approach has the following advantages. First, in initial application development, designers are able to select components to implement activities independently of one another. Potential mismatches generally are handled by coordination processes. Also, dependencies are managed routinely by coordination processes based on systematic design frameworks. Additionally, a process repository 30, used as a handbook, suggests alternative ways of implementing activities and dependencies.
Second, during application maintenance, designers often need to change the implementation of activities, in order to reflect changes in functional requirements. Applications can be reconstructed easily after such changes by reusing the same architectural diagram and simply managing the dependencies of the affected activities with the rest of the system. Additionally, when applications are ported to a new environment, their abstract architecture (activities and dependencies) remains unaffected. However, the use of different coordination processes might be required. By making dependency management routine, the new environment may be managed readily and a new application may be constructed quickly from the original architectural description and functional components.
There are several modifications that may be made to the architectural description language, and associated tools and repositories, from the particular exemplary embodiment shown above.
For example, all activities and dependencies currently have a statically fixed number of ports. In other words, each activity knows at design time how many and which other activities it might interact with. In many real systems, interaction patterns are determined dynamically during run-time and might vary during the lifetime of an execution. To be able to model such systems, the architectural description language may be extended with activity and dependency constructs that represent sets of indefinite run-time determined cardinality.
The architectural description language described above also uses attribute definitions for expressing architectural assumptions. Although attribute definitions seem to be powerful enough to express a number of relationships and constraints, systematic guidelines on how and when to use them may be provided by classifying and standardizing architectural assumptions the way these assumptions are expressed.
Although the vocabulary of dependencies described above in connection with the repository of coordination processes is capable of describing a large number of commonly occurring relationships, it is merely illustrative and is neither limiting nor complete. As non-trivial software applications are developed and implemented, additional relationships may be encoded as special cases of existing dependency types, or as new dependency types. Likewise, the design space of coordination processes can be enriched by new generic processes, or by new special cases of existing generic processes.
In particular, commonly occurring composite patterns of dependencies, for which efficient joint coordination processes have been developed, could be represented. One example is the joint management of a set of unidirectional flows through the network by combining the respective data items into a single packet. The existence of a library of such composite entities will enable automated design assistants to scan application architectural descriptions, discover patterns of simpler dependencies that correspond to composite dependencies, and efficiently manage them using joint coordination processes.
Design rules can also be added to automate the selection of a particular coordination process from among multiple compatible coordination processes for a given dependency. Such design rules may help automate this selection step, for example, by ranking candidate processes according to various evaluation criteria such as their response time, their reliability, and their overall fit with the rest of the application. For example, when managing a data flow dependency, one possible design heuristic would be to use direct transfer of control, e.g., remote procedure calls, when the size of the data that flows is small, and to use a separate carrier resource, such as a file, when the size of the data is large.
The present invention may also be used to provide applications in varying architectural styles, such as client-server, pipe-filter, and event-based architectures. In particular, by selecting different coordination processes of a particular architectural style, the same set of components can be organized into applications conforming to different architectural styles. In addition, the multidimensional design space of coordination processes discussed above can thus provide a useful vehicle both for defining styles as combinations of design choices, and for providing more specific guidelines as to which design choices are consistent with a desired architectural style. For example, event-based architectures exclude the management of dependencies using push or pull organizations. Furthermore, our design space could help invent and characterize new architectural styles.
Other improvements may be made to improve performance of this system. For example, before managing a dependency, an exhaustive search of candidate coordination processes is performed applying the compatibility checking algorithm of
While emphasis above was placed on having a handbook of coordination processes, this system is also particularly well-suited for building repositories of generic and specialized architectures in a wide variety of domains. Such repositories of domain-specific architectures or software architecture handbooks, could serve as useful starting points for designing any new system. For example, when starting the design of a new application, designers first consult the handbook, in order to retrieve alternative generic architectures of similar systems. They can then specialize those generic architectures to fit their particular needs.
The properties of this architectural description language also suggest structures for new programming languages that separate the core function of software components from their application-specific interconnection protocols. Such programming languages should define components which interact with their environment through input and output resource ports only. In addition every input and output port of a component should be independently managed. That is, every input resource expected by a component should be independently produced and made accessible to the component. Likewise, every output resource should be independently made accessible to its consumers. Every input port should be connected to an arbitrary number of producers and every output port an arbitrary number of consumers. Finally, components should make no assumptions about exclusive or shared ownership of resources. If necessary, coordination support for sharing resources should be defined completely outside the component. A conventional programming language construct that more closely satisfies these properties is a sequential block of code which receives all its inputs and leaves all its outputs to independent local variables. An appropriate programming language should offer explicit support for abstractions with such properties.
Having now described a few embodiments of the invention, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by way of example only. Numerous modifications and other embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the invention as defined by the appended claims and equivalents thereto.
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|Sep 21, 2009
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