A model-declared function is a function that is declared in a conceptual model, but is not defined in that conceptual model. The function might be defined in the hosting or storage environment. For example, a model-declared function might be mapped to a function that is defined in a database, thus exposing server-side functionality in the conceptual model.
The declaration of a model-declared function contains the following information:
The name of the function. (Required)
The type of the return value. (Optional)
If no return value is specified, the return type is void.
Parameter information, including parameter name and type. (Optional)
The ADO.NET Entity Framework uses a domain-specific language (DSL) called conceptual schema definition language (CSDL) to define conceptual models. In CSDL, one implementation of a model-declared function is a function import. The following CSDL defines an entity container with a function import definition. Note that the return type for the function is void since no return type is specified.