->A CDS entity cannot be used as a data type in ABAP Dictionary.
->In ABAP Dictionary, the CDS database view can be used like any classic structure, such as the type of a substructure, as an include structure, or as the row type of a table type.
-> In ABAP, a CDS entity can be specified after the TYPE addition to reference its structure type and its components in ABAP programs.
->The CDS database view is the technical foundation of the CDS view in ABAP Dictionary. It is a read-only classic database view.
->A CDS view has two types of keys:
->For CDS entities, KEY can be used to define key elements. This key is the semantic key of the CDS view.
-> The key of the CDS database view is determined implicitly, as in a classic database view. This key is the technical key of the CDS view.
In ABAP SQL, the key used is determined according to whether the name of the CDS entity or the name of the CDS database view is used to access a CDS view. Recommendation is to use CDS entity name in ABAP.