Interface views are a special type of view that consist only of a definition of fields and a reference to another view.
An interface view has a schema, and all possible implementations have to fulfill this schema (the same fields and types).
As an interface can be implemented by different views, each possible implementation can have a different primary key, so it makes no sense for the interface views to have primary keys by themselves. The primary keys will be inherited from the implementation. For this reason, in the VDP admin tool, it is not possible to see the primary key for an interface. In any case, the primary key is going to be recognized by other clients when querying the interface if the view implementing the interface has one.
For instance, accessing an interface via the provided RESTful web services using:
will display the Self column if the view implementing the interface has a primary key. On the other hand, if the implementation view does not have a primary key set the Self column will not be present in the response of the RESTful web service.