1. A method implemented by a computer in response to execution of program code by a processor of said computer, comprising: acquiring metadata defining a first object model including extensible entities, the first object model comprising an instance of a metaobject; acquiring metadata defining an extension object model, the extension object model to extend at least one of the extensible entities of the first object model; and merging the object model and the extension object model to create metadata defining an extended object model, the extended object model comprising an instance of the metaobject.