[Esip-preserve] a new relation type for subset citations

[Greg Janée]

The RDA data citation working group has recommended that subsets of datasets (more broadly, queries against datasets) be persistently identified upon request; cf. https://www.rd-alliance.org/group/data-citation-wg/wiki/wgdc-recommendations.html.
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For this to work, queries have to be stored *somewhere*.  One approach (this appears to be the RDA group's working assumption) is for the provider to take on the burden of permanently storing queries, and from there it can issue PIDs for those queries by whatever means it has available.  Another approach is for the provider to support a query API of some kind, e.g., query URLs (think http://dataset?query=this+that+and+the+other).  This may result in lengthy URLs, but an external identifier system can be used to assign short, opaque PIDs that redirect to those query URLs.

Regardless of the approach taken, the net result is multiple, related PIDs: one PID for the dataset as a whole, and then multiple PIDs, one per stored query.  It would be beneficial to record the relationship between these identifiers, particularly in the case when an external identifier system is being used.  The DataCite metadata schema (http://schema.datacite.org) lists a number of possibilities, but none quite fit:

- IsPartOf/HasPart: "A IsPartOf B" implies that B can be broken down into some disjoint pieces, and A is one of those pieces.  But a cited subset is not a disjoint part of a whole.

- IsCitedBy/Cites: "A IsCitedBy B" implies that B mentions A in some way, and is possibly intellectually derived from A, but not necessarily.  This is intentionally a pretty vague relationship (as vague as publication citations, right?), whereas a cited subset has a very specific relationship to the whole.

- IsReferencedBy/References: same thing.

- IsMemberOf/HasMember (a newly proposed relation): "A IsMemberOf B" implies that B has some rules or standards for inclusion, and A satisfies those rules.  Doesn't seem applicable in this case.

So I'm wondering if we need a new relation, which I'll provisionally call "IsCitedSubsetOf".  "A IsCitedSubsetOf B" would mean that a reference to A is really a reference to B, but only a subset of B was actually used.  Note that I didn't call it IsSubsetOf, for that would bring up the same issues that IsPartOf has.  It seems important to record that the purpose of these query PIDs is for citation and nothing else.

Thoughts?
-Greg