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)
Note: 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.