HQDM Serialisation Format for Data Sharing

[twalmsley]

HQDM has no standard textual for its data models, but one would be needed to make data sharing easier.

MagmaCore uses RDF and can serialise data as TTL, but not everyone will be using triple stores and RDF to work with their data models, so a standard format needs to be developed for data exchange.

[twalmsley]

I now think we can rely on RDF as the data interchange format since we can export models as TTL, XML, CSV, etc. which just leaves the problem of defining HQDM in RDF. There is a tentative version of this here, which is useful for some inferencing tasks, but it still needs work.