[Nml-wg] id/idref and inverse relations

[Jeroen van der Ham]

Hello all,

During the call last week we discussed a use-case brought up by Aaron:

A client domain may want to correct locally how a Link is connected by them, but this Link is originally described by the Provider.

We have done some back-and-forth on the GridForge site and it has become a rather lengthy discussion, raising several different issues, which have become further reaching than we originally thought:

- Allow the use of idRef as the subject[0] of a Relation
- Allow the inverse definition of a relation
- How does authority come into descriptions

[0]: I'm using the RDF (subject --predicate-> object) interpretation of "subject" here.

Allow the use of idRef as subject:
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I was not sure whether we ever decided on this. So far I have only seen examples of elements with "id" attributes as subjects of relations, no "idRef".
As far as I understand it, the intention of the "id" attribute is to create and define an object. It can then later be used as object of Relations using idRef.

If we allow idRef's also as subjects, it means that there is no longer a single place in a file or set of files where an object is defined.
I have no idea whether this is required, but this should probably be noted as a caveat for implementation.

Allow the inverse definition of a relation
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The above "single place of description" also applies when we allow inverse definitions.

The definition of an inverse for a one-to-one relation is simple. However it is not so clear how to define the inverse of a one-to-many relation, even more so when ordering is required. The simplest solution would then be to use an explicit group concept.

Authority of descriptions
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We have not discussed trust and authority of topology descriptions so far. This is something that at some point we have to say something about, also whether it is in scope or not.
Either way, if we allow the above constructs, we at least lose the single place of description, which may be a possible mechanism for authority and trust.


Was it the intention that idRef as subject was already allowed? If not, do we want to allow it now?
Are there any other implications of using idRef as subject?

Do we want to allow inverse relations? If so, how do we handle the many-to-one relations?

Jeroen.