md:Statement is problematically defined

[VladimirAlexiev]

Header-AP-Voc-RDFS2020.ttl defines:

• md:Statement rdfs:comment "It represent a set of Definition and/or Description elements."
  • But a statement (triple) is not a set of elements, it has exactly 3 parts. And "Definition and/or Description elements" doesn't relate to any
• md:Statement.subject, md:Statement.predicate, md:Statement.object are defined as cims:dataType cim:String
  • but RDF resources in a triple are not strings: they can be URLs, blank nodes or resources
  • only the object may or may not be a string
  • So you better leave out that cims:dataType and don't define any range

[VladimirAlexiev]

CompleteDatatypeMap.properties also mis-defines these terms

• rdf:Statements.object rdf:Statements.predicate rdf:Statements.subject
  (the correct terms are rdf:Statement and rdf:object rdf:predicate rdf:subject
• In a hijacked namespace
• With wrong type xsd:string (should be rdf:Resource)

[griddigit-ci]

the statement part is all related to the difference model and we need to clean that up

[VladimirAlexiev]

@griddigit-ci @Sveino do you agree to delete md:Statement, rdf:Statement, rdf:Statements?
Using this is a terribly inefficient way to capture triples.

We should just use rdfg:Graph (see #53 (comment))