You have the following CDS definition (aliases shown):define view entity Z_ENTITYas select from Z_SOURCE1 as...

Comprehensive and Detailed Explanation From Exact Extract:

In a CDS view entity defined AS SELECT FROM, the association ON condition must use the source aliases defined in the FROM clause.

$projection is used in projection views (AS PROJECTION ON …), not in a basic select view entity. Therefore, options using $projection (B, C) are invalid here.

Using global names (Z_SOURCE1, Z_SOURCE2) in the ON (A) ignores the declared aliases and is not the recommended/valid form within the view definition.

The correct ON clause uses the aliases _Source1 and Source2 with the matching key fields:ON _Source1.carrier_id = Source2.carrier_id (D).

This aligns with CDS modeling rules in RAP: use aliases consistently and model associations with precise ON conditions based on keys.

Study Guide Reference: ABAP CDS Development—Associations & ON conditions; RAP Data Modeling.