In a given Core Data Services View Entity Data Definition, which types of sources are allowed?

The correct answer is C, which refers to a CDS DDIC-based view. Core Data Services (CDS) views are designed to provide a semantic layer on top of database tables and other database objects, facilitating complex querying and data modeling directly in the database.

CDS views can be based on other CDS views (such as DDIC-based views), enabling the use of reusable database artifacts. This promotes modular design and allows developers to build upon existing business logic encapsulated in other CDS views. The ability to reference these views allows for more complex data models and simplifies data consumption, as users can interact with a higher-level abstraction rather than underlying tables directly.

In contrast, the other options describe various database objects, but they are not designed to represent the same level of sophisticated data modeling that CDS views offer. For instance, while a database table, an external view, and a structure can be sources of data, they do not carry the same semantic capabilities or allow for the same level of composability as CDS views. Thus, the selection of a CDS DDIC-based view as the correct option highlights the advanced capabilities provided by CDS in the context of developing enterprise applications using ABAP.