11. A computer program product for implementing a method for mapping between a declarative type and a dynamic runtime type, the computer program product comprising one or more physical storage media having stored thereon computer-executable instructions that, when executed by one or more processors of the computing system, cause the computing system to perform the method, the method comprising: an act of a customized declarative language reader accessing an activity that is defined using a declarative language, and that is configured to be executed within a continuation-based runtime, the activity including a fully modeled declarative type written in declarative markup, the declarative type including one or more members which define a data flow for the declarative type, each member being defined within a declarative tag in the declarative markup and including a name and a type of input for the member, wherein the declarative markup also includes an identification of a schema to be used to determine how the fully modeled declarative type is to be interpreted at runtime by the continuation-based runtime including how the one or more members of the declarative type are to be mapped to properties of a dynamic runtime type; an act of the customized declarative language reader creating a dynamic runtime type based on the fully modeled declarative type, creating the dynamic runtime type comprising generating, based on the schema defined in the declarative program, a type in memory without creating a common language runtime type to represent the declarative type; an act of the declarative language reader generating a mapping from the accessed declarative type to the created dynamic runtime type using the mapping schema, generating the mapping including mapping each member of the declarative type to a property of the created dynamic runtime type; and an act of interpretively executing the dynamically constructed dynamic activity type within the continuation-based runtime at a first process, such that the dynamic activity type is executed without compilation, and during execution of the dynamically constructed dynamic activity type: pausing execution of the dynamically constructed dynamic activity type at the first process; and resuming execution of the dynamically constructed dynamic activity type at a second, different process.
11. A computer program product for implementing a method for mapping between a declarative type and a dynamic runtime type, the computer program product comprising one or more physical storage media having stored thereon computer-executable instructions that, when executed by one or more processors of the computing system, cause the computing system to perform the method, the method comprising: an act of a customized declarative language reader accessing an activity that is defined using a declarative language, and that is configured to be executed within a continuation-based runtime, the activity including a fully modeled declarative type written in declarative markup, the declarative type including one or more members which define a data flow for the declarative type, each member being defined within a declarative tag in the declarative markup and including a name and a type of input for the member, wherein the declarative markup also includes an identification of a schema to be used to determine how the fully modeled declarative type is to be interpreted at runtime by the continuation-based runtime including how the one or more members of the declarative type are to be mapped to properties of a dynamic runtime type; an act of the customized declarative language reader creating a dynamic runtime type based on the fully modeled declarative type, creating the dynamic runtime type comprising generating, based on the schema defined in the declarative program, a type in memory without creating a common language runtime type to represent the declarative type; an act of the declarative language reader generating a mapping from the accessed declarative type to the created dynamic runtime type using the mapping schema, generating the mapping including mapping each member of the declarative type to a property of the created dynamic runtime type; and an act of interpretively executing the dynamically constructed dynamic activity type within the continuation-based runtime at a first process, such that the dynamic activity type is executed without compilation, and during execution of the dynamically constructed dynamic activity type: pausing execution of the dynamically constructed dynamic activity type at the first process; and resuming execution of the dynamically constructed dynamic activity type at a second, different process. 12. The computer program product of claim 11 , wherein the schema for mapping from a declarative type to a dynamic type is swappable.