DataService protocol mapped to dct:conformsTo

[jakubklimek]

Problem statement
In GeoDCAT-AP 2.0.0, the Data Service Protocol is mapped to the dct:conformsTo property on Data Service via the information in the Controlled Vocabularies section and in B.6.4 Resource locator - *On-line resource, and it is mapped to a specific INSPIRE Registry: Protocol values code list.

It is not identified as a separate property profile yet though.

This makes correct assignment of usage notes, labels and the required code lists rather difficult, as well as consequent validation e.g. via SHACL.
The current approach is not in line with the profiling guidelines established in the context of the SEMIC Style Guide property reuse guideline Reuse of a property with terminological adaptations and Reuse of a property with semantic adaptations.
Also, the approach becomes even more problematic in a cross-profile environment where incompatible requirements can be easily made.

The dct:conformsTo usage note says e.g. This property is used to indicate the general standard or specification that the Data Service endpoints implement.

Related to #94

Proposal
Either

1. Merge the usage notes to the generic dct:conformsTo to make it clear that Data Service protocols are one kind of the Standards expected as values here, or
2. Introduce a profile specific subproperty of dct:conformsTo geodcatap:serviceProtocol and attach the separate usage notes there.