Batch requests: Referencing values from response bodies more generally

[HeikoTheissen]

OData-Protocol, section 11.7.6 states:

Alternatively, a value reference can consist of a $ character followed by the value of an instance annotation with term Core.ContentID (see OData-VocCore) that occurs in the payload of the preceding request as described in section 11.4.2.2 and section 11.4.3.1, then the referenced value is the corresponding value in the response, which the service SHOULD annotate with the same Core.ContentID value.

This is too narrow. Core.ContentID instance annotations may also appear in responses to other types of request, for example, action invocations.

[ralfhandl]

TC 2024-08-28: for the existing cases (insert, update) the relationship between ContentIDs in request and response is "canonical". For actions this is less clear.

@HeikoTheissen to follow up on this relationship and reduce the amount of out-of-band knowledge.

@ralfhandl & @HeikoTheissen to find out which parts of content-id referencing are already implemented by SAP.

[ralfhandl]

TC agrees that the new functionality can be purely provided via vendor-specific extensions and no changes to the Core specifications are needed.