This page is a subpage of CMDI 1.2

Allowing only a single reference from a component (or element) to a resource proxy

The issue

With OAI-PMH its possible to retrieve multiple records with one request. When one validates the returned document its possible that IDs clash, as they are unique within the original XML document but there was no requirement that they should have been globally unique.

Proposed solutions

First solution

It's possible in XSD to limit the scope of IDs and IDREFs using xs:key and xs:keyref. This solution has been described in the CmdiMultipleRecords page. A showstopper for this solution is currently that @ref can refer to multiple ResourceProxies, i.e., the type of @ref is IDREFS, while there is no xs:keyrefs. A solution in CMDI 1.2 would be to make the type of @ref IDREF again as it was once. An investigation of the around half million harvested CMD records shows that instances of ​collection profile are currently the only users of this feature, e.g., the ​IPROSLA Abel CMD collection record. Here the root collection component refers to all the ResourceProxies. Its debatable if that is needed, as this should be the default interpretation if there is no @ref.

Pros

CMD records can be concatenated for bulk retrieval.

Cons

There are CMD records that currently use multiple ResourceProxy references in one @ref.

Centre impact

When a centre uses references to multiple resource proxies in one @ref these would have to be modeled differently.

Implementation examples

See the CmdiMultipleRecords page.

Discussion

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Tickets

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