FIELD OF THE INVENTION 
     The present invention is generally directed to computer controlled manufacturing systems, and more particularly to control of application programs in a multi-tiered computing arrangement. 
     BACKGROUND OF THE INVENTION 
     Early computer controlled manufacturing arrangements, for example, those for manufacturing semiconductors, generally included a central computer system for controlling the overall factory floor. Coupled to the central computer system, via a network for example, were satellite computers programmed for respectively controlling selected tools. The tools were often directly coupled to serial or parallel ports or special adapter cards of the satellite computers. 
     The early systems generally controlled a single tool with a single satellite computer. Thus, a single process running on the single computer provided communication between the central computer system and the single tool. As manufacturing output requirements increased, additional tools were coupled to the satellite computers. To establish the required communications between the central computer system and the newly added tools without incurring undesirable delays associated with developing new software, replicated processes were used. Specifically, for each tool coupled to a satellite computer, a respective process executing on the satellite computer provided the necessary communication interface between the central computer system and the tool. 
     The total commuter and human resources consumed by adding new processes each time new tools are coupled to satellite computers has become significant. Generally, the resource requirements are some function of the number of satellite computers and the number of tools. Thus, in a large manufacturing arrangement, the resource requirements can be considerable. Therefore, a system and method that addresses the above identified problems is desirable. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method is provided for inter-tier application control in a multi-tier computing environment that includes a first tier application program, a second tier application program, and a plurality of third tier control elements, wherein the second tier application program initiates processing of the third tier control element in response to messages from the first tier application program. The method comprises associating connection identifiers that respectively reference connections between the second tier application program and the third tier control elements with respective third tier control element identifiers. For messages that are sent from the first tier application program to the second tier application program to initiate processing sequences by the third tier control elements, respective third tier control element identifiers are indicated for the messages, The second tier application program performs application specific processing on the messages, and connections are selected for transmitting control messages to the third tier control elements based on the indicated third tier control element identifiers and the associated connection identifiers. 
     In another embodiment, a method comprises associating connection identifiers that respectively reference connections between the second tier application program and the third tier control elements with respective third tier control element identifiers and receiving a message from the first tier application program. A third tier control element identifier based on the message is indicated to the second tier application program, and the second tier application generates a control message. The control message is transmitted to a third tier control element via a selected connection that is based on the indicated third tier control element identifier and associated connection identifier. 
     An apparatus is provided for inter-tier application control in a multi-tier computing environment that includes a first tier application program, a second tier application program, and a plurality of third tier control elements, wherein the second tier application program initiates processing of the third tier control element in response to messages from the first tier application program. The apparatus comprises means for receiving messages from the first tier application by the second tier application; means for mapping messages received from the first tier application to respective connections between the second tier application and the third tier control elements) and means for transmitting control messages generated from the received messages to the third tier control elements via the respectively mapped connections. 
     In another embodiment, a multi-tier computing arrangement is provided that comprises: a first tier computer system arranged to host a first tier application program; a plurality of third tier control elements; and a second tier computer system coupled to the first tier computer system and to the third tier control elements and arranged to host a second tier application program. The second tier application program includes: a first connection layer arranged to receive messages from the first tier application program; a first mapping layer arranged to indicate to the second tier application program a third tier control element identifier based on the message and associate connection identifiers that respectively reference connections between the second tier application program and the third tier control elements with respective third tier control element identifiers; a core logic layer arranged to generate a control message; a second is mapping layer arranged to select a connection to a third tier control element based on the indicated third tier control element identifier and associated connection identifier; and a second connection layer arranged to transmit the control message via the selected connections. 
     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more completely understood upon consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
     FIG. 1 illustrates a computer controlled manufacturing arrangement in which multiple levels of application programs control the manufacturing process; 
     FIG. 2 is a block diagram of a prior art computer controlled manufacturing arrangement in which an instance of a first tier application executing on computer system interacts with multiple instances of a second tier application executing on computer system to control a manufacturing process; 
     FIG. 3 is a block diagram of a computer controlled manufacturing arrangement according to an example embodiment of the invention; 
     FIG. 4 is a block diagram of layers of software with which the core logic of the second tier application interacts in communicating with the first tier application and the tool is control element; 
     FIG. 5 is a flowchart of processing performed for initialization of mappings of sockets used by the second tier application for communication with the first tier application and with the tool control elements according to an example embodiment of the invention; 
     FIG. 6 is a flowchart that shows the processing performed when the second tier application receives a message from the first tier application, according to an example embodiment of the invention; and 
     FIG. 7 is a flowchart that shows the processing performed when the second tier application receives a message from one of the tool control elements, according to an example embodiment of the invention. 
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The present invention is believed to be applicable to a variety of multi-tiered computing arrangements. The invention has been found to be particularly advantageous in a computer controlled semiconductor manufacturing arrangement in which multiple levels of application programs executing on various computer systems interact in the manufacturing process. While the present invention is not so limited, an appreciation of various aspects of the invention is beat gained through a discussion of various example applications described below. 
     Referring first to FIG. 1, a computer controlled manufacturing arrangement  100  is shown in which multiple levels of application programs control the manufacturing process. A first tier application  102  executes on a computer system  104 , a second tier application  106  executes on a computer  108 , and tool control elements  110   a-d  control operation of the respective manufacturing tools  112   a-d . In an example embodiment, the first tier application  102  is manufacturing control software such as Workstream software that is commercially available from Consilium. The second tier application  106  is tailored to the specific needs of the manufacturing arrangement  100  and the particular tools  112   a-d  to be controlled. For example, the tools  112   a-d  are TEL-ALPHA-VII vertical furnaces that are available from Tokyo Electron Limited. The second tier application generally makes decisions based on selected business rules and then directs the tool to perform certain tasks in a specified order. An example computer controlled manufacturing arrangement in which the present invention may be embodied is described in U.S. Pat. No. 5,751,581 to Tau et al., entitled, “MATERIAL MOVEMENT SERVER,” and herein incorporated by reference. 
     The tool control elements  110   a-d  of tools  112   a-d  may be viewed as third tier application programs and may be embodied in various forms depending on the particular tool. For example, a tool control element may be a programmed microprocessor that is coupled to the second tier application  106  via a network  114 , wherein the second tier application  106  and tool control elements  110   a-d  communicate according to the TCP/IP. Alternatively, the second tier application  106  and tool control elements  110   a-d  may communicate via RS-232 using the SECS protocol. 
     While not shown, it will be appreciated that the manufacturing arrangement  100  may include additional machines, tools, control programs, and computer systems according to particular manufacturing requirements. For example, the arrangement  100  may include a track system for transporting material and work-pieces between tools. The arrangement may also include additional tools for performing other functions such as for etching, testing, and inspecting semiconductors. 
     FIG. 2 is a block diagram of a prior art computer controlled manufacturing arrangement  200  in which an instance of a first tier application  102  executing on computer system  104  interacts with multiple instances  106   a-d  of a second tier application executing on computer system  108  to control a manufacturing process. Interaction between the first tier application  102  and the tool control elements  110   a-d  occurs via respective instances  106   a-d  of the second tier application. The instances  106   a-d  of the second tier application are processes that execute on the system  108 , each operating out of its own memory space. Example “processes” are those supported by the UNIX operating system. 
     In the example arrangement  200 , the tool control elements  110   a-d  are generally identical and control generally identical tools (not shown). Thus, the core logic  201   a-d  of the instances  106   a-d  of the second tier application are essentially identical, wherein the core logic refers to the manufacturing control functions performed by the application. 
     Each of the instances  106   a-d  of the second tier application manages two sockets, one for communicating with the first tier application  102  and one for communicating with one of tool control elements  110   a-d . Such sockets can be TCP/IP sockets to support two-way communication, for example. To illustrate, instance  106   b  manages a socket  202  to communicate with the first tier application  102  via socket  204  of the first tier application. Bi-directional line  206  illustrates the two-way communication. Similarly, instance  106   b  manages socket  208  to communicate with tool  110   b . While not shown, it will be appreciated that the tool control elements  110   a-d  include compatible software and circuitry for socket-based communication with the instances  106   a-d  of the second tier application. 
     For the first tier application  102  to interact with one of the tool control elements, e.g.,  110   b , the first tier application  102  selects the socket, i.e.,  204 , to communicate with the instance  106   b  of the second tier application that is dedicated to interacting with the tool control element  110   b . The first tier application  102  then sends a message via socket  204  to the instance  106   b  of the second tier application. For the purpose of communicating with tool control element  110   b , the instance  106   b , being dedicated to tool control element  110   b , does not need tool identification information in the message from the first tier application  102 . 
     The multiple instances  106   a-d  of the second tier application can create problems in administering the computer system  108 . Specifically, memory demands of the multiple instances may necessitate a system that is prohibitively expensive. In addition, secondary storage needs (for example, hard disk space) for respective files used by the instances  106   a-d  may require excessive operator support for tracking the files. 
     FIG. 3 is a block diagram of a computer controlled manufacturing arrangement according to an example embodiment of the invention. A single instance  302  of the second tier application  106  manages communications with the first tier application  102  and the tool control elements  110   a-d  The single instance  302  reduces memory requirements and avoids unnecessary duplication of files. 
     In the arrangement  300  where there is a single instance  302  of the second tier application, for a message from the first tier application  102  to be processed and sent to one of the tool control elements, e.g.,  110   b , there must be an association between the sockets  306  and the respective tool control elements  110   a-d , as well as an association between the sockets  308  and the respective tool control elements  110   a-d . The association of sockets to tools is required because the core logic of the second tier application does not require nor does it provide an indication of a desired tool control element for a particular message from the first tier application  102 . 
     The embodiment of FIG. 3 includes multiple corresponding sockets between the first tier application  102  and the second tier application  302 . Specifically, sockets  310  of the first tier application  102  correspond to sockets  306  of the second tier application  302 , respectively. In an alternate embodiment where the first tier application  102  and the second tier application  302  communicate via the ISIS message bus, a single socket is used for communication between the first and second tier applications, and message identifiers and task entry points are used for routing messages. 
     FIG. 4 is a block diagram of layers of software with which the core logic  352  of the second cite application  106  interacts in communicating with the first tier application  102  and the tool control element  110 . A socket layer  354  provides a socket based interface for the second tier application  106  to the first tier application  102 . In an example embodiment, the socket layer is comprised of an application embodied in Smalltalk software from Object Share. Similarly, the socket layer  356  provides a socket based interface for the second tier application to the tool control element  110 . 
     To achieve the single instance of the second tier application  302  as shown in FIG. 3, two layers of mapping logic  358  and  360  are provided between the core logic  352  and the socket layers  354  and  356 , respectively. Mapping logic  358  maps sockets used by the second tier application  106  to communicate with the first tier application  102  to respective tools. To illustrate, reference is made back to FIG.  2 . In FIG. 2, recall that socket  202  is used by the first tier application  102  to communicate with tool control element  110   b  for controlling tool  112   b . Relative to the present invention, mapping logic  360  maps tools to sockets that are used to communicate with the tool control elements  110   a-d . The socket  208  of FIG. 2, for example, would be mapped to the tool controlled by tool control element  110   b . 
     FIG. 5 is a flowchart of processing performed for initialization of mappings of sockets used by the second tier application  302  for communication with the first tier application  102  and with the tool control elements  110   a-d  according to an example embodiment of the invention. At block  502 , socket connections are established between the second tier application  302  and the first tier application  102 . Because the first tier application  102  uses respective dedicated sockets for controlling the tools  112   a-d , the second tier application  302  establishes corresponding sockets  306  . In the ISIS embodiment, the first and second tier application each create a single socket for communication, and no first tier mappings are required. 
     At block  504 , the socket connections are “mapped” to or “associated” with respective tool control identifiers, as shown below, for example: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 socket first tier  1 --&gt; 
                 tool A 
               
               
                   
                 socket first tier  2 --&gt; 
                 tool B 
               
               
                   
                 socket first tier  3 --&gt; 
                 tool C 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 socket first tier  n --&gt; 
                 tool X 
               
               
                   
                   
               
             
          
         
       
     
     The notation “socket first tier ” refers to the sockets  306  of the second tier application that are used for communication with the first tier application  102 , The mapping is used by the mapping logic layer  358  to identify the one of tools A-X for which a message from the first tier application  102  is intended. In the ISIS implementation, respective entry points are created for the different tools. 
     Respective socket connections  308  are established at block  506  for providing communication between the second tier application  302  and the tool control elements  110   a-d . At block  508 , the tool identifiers are respectively mapped to the sockets  308  used for communication with the tools as shown below, for example: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 tool A --&gt; 
                 socket tool  1 
               
               
                   
                 tool B --&gt; 
                 socket tool  2 
               
               
                   
                 tool C --&gt; 
                 socket tool  3 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 . 
               
               
                   
                 tool X --&gt; 
                 socket tool  n 
               
               
                   
                   
               
             
          
         
       
     
     This map is used by the second tier application  302  select a socket tool  for communication with one of tool control elements  110   a-d  after having received and processed a message from the first tier application  102 . 
     FIG. 6 is a flowchart that shows the processing performed when the second tier application  302  receives a message from the first tier application  102 , according to an example embodiment of the invention. At block  532  a message is received via conventional socket layer  354  processing. Blocks  534  and  536  comprise actions performed by the mapping logic layer  358 . Specifically, the tool identifier that is mapped to the one of sockets  306  over which a message was received is obtained from the map and added to the message. The identifier can be inserted in an unused portion of a packet containing the message or appended to the end of the message so as to be ignored by the second tier application core logic  352 . 
     In the ISIS embodiment, tasks are associated with entry points in the second tier application core logic  352  for the respective tools. Thus, based on the task referenced in the message, the associated tool identifier is inserted in the message. 
     The processing of the core logic  352  is performed at block  538 . Blocks  540  and  542  comprise actions performed by the mapping logic layer  360 . Specifically, the tool identifier that was added to the message at block  536  is obtained, and the one of sockets  308  that is mapped to the tool identifier is selected. At block  544 , the socket layer  356  processing is performed to send the message to one of the tool control elements  110   a-d.    
     FIG. 7 is a flowchart that shows the processing performed when the second tier application  302  receives a message from one of the tool control elements  110   a-d , according to an example embodiment of the invention. At block  572  a message is received via conventional socket layer  356  processing. Blocks  574  and  576  comprise actions performed by the mapping logic layer  360 . Specifically, the tool identifier that is mapped to the one of sockets  308  over which a message was received is obtained from the map and added to the message. The identifier can be inserted in an unused portion of a packet containing the message or appended to the end of the message so as to be ignored by the second tier application core logic  352 . 
     The processing of the core logic  352  is performed at block  578 . It will be appreciated that in most circumstances a message from one of the tool control elements  110   a-d  will not result in a message being sent outside the second tier application core logic  352 . In these cases, no further processing occurs relative to the invention. However, some messages from the tool control elements  110   a-d  will result in further messages sent from the second tier application  302  to the first tier application  102 , in which case the processing shown by blocks  580  and  582  occurs. 
     Blocks  580  and  582  comprise actions performed by the mapping logic layer  358 . Specifically, the tool identifier that was added to the message at block  576  is obtained, and the one of sockets  306  that is mapped to the tool identifier is selected. At block  584 , the socket layer  354  processing is performed to send the message to one of the tool control elements  110   a-d   
     In the ISIS embodiment, the tool identifier is used to identify a task identifier, which in turn is used as input to a process group look-up function. The process group look-up function returns the address of the first tier application  102 . 
     In a particular example ISIS embodiment, a message originates at the first tier application, for example a Workstream session, and is encoded into a Reliable Distributed Object (RDO) format message. This message contains the process information for a particular lot or batch of lots of semiconductor wafers. The message is then broadcast using ISIS to a waiting second tier application, for example an equipment interface computer, for the particular tool being controlled. 
     The second tier application receives and decodes the RDO message and creates an application specific Smalltalk object. The Smalltalk object is then accessed to gather the necessary information that governs how the tool is to process the next lot or batch of wafers. Once the application specific rules of the second tier application have been applied to determine what action to perform, the appropriate information is sent to a tool control element in a semiconductor equipment communication standard (SECS) message. The message is streamed to the tool control element via an RS-232 communication link. 
     As noted above, the present invention is applicable to a number of different multi-tier computing arrangements. Accordingly, the present invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent structures, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art upon review of the present specification. The claims are intended to cover such modifications and devices.
A system and method for providing inter-tier application control in a multi-tiered computer computing environment. In an example embodiment for a multi-tier computing environment that includes a first tier application program, a second tier application program, and a plurality of third tier control elements, connection identifiers that respectively reference connections between the second tier application program and the third tier control elements are associated with respective third tier control element identifiers. When the second tier application program receives a message from the first tier application program, mapping software indicates to the second tier application program a third tier control element identifier based on the message. A control message generated by the second tier application program is transmitted to a third tier control element based on the indicated third tier control element identifier and the associated connection.