1. A system to process a declaratively-specified computer application, the system comprising a memory and a processor to provide a functionality of the declaratively-specified computer application, the processor configured to: interpret a structure specification representing a general data model; interpret a behavior specification, wherein the behavior specification uses said general data model represented by said structure specification and specifies a behavior of the application; and process the behavior specified by said behavior specification, wherein to process the behavior, the processor is configured to: identify a behavior component in said behavior specification; and perform a purpose-oriented processing of said behavior component as specified by the behavior specification, wherein the purpose-oriented processing comprises: identifying a behavior component implementation, wherein said behavior component implementation is based on a processing concrete data model, said processing concrete data model is derivable from said structure specification or said general data model; interpreting an application data item using said processing concrete data model, the application data item being accessible to the system or transferable to the system, wherein the transfer of the application data item to the system comprises: deriving a transfer concrete data model from said structure specification or said general data model, wherein the transfer concrete model represents data model essential for transferring application data items; obtaining the type of the transfer operation to be performed; demarcating said application data item if the type of operation is export; transferring the demarcated application data item to a receiving system, wherein the receiving system is external to the system; and importing the received application data items to be interpreted using the transfer concrete model if the type of operation is import, and, optionally, to be merged with any corresponding artifacts on the system; and executing said behavior component implementation to process the application data item using said processing concrete data model and as specified by said behavior component.