> From [log in to unmask] Fri Feb 16 14:47 MET 2001
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> Date: Fri, 16 Feb 2001 14:36:43 +0100
> From: Thomas Baker <[log in to unmask]>
> Subject: URIs: archival precision vs fuzzy persistence
> To: [log in to unmask]
>
> There seem to be two equally important but contradictory requirements
> regarding versioning and namespaces:
>
> Archival precision. The requirement for archival precision suggests
> that successive versions of metadata terms have unique (and persistent)
> identifiers. Unique identifiers are necessary for reconstructing the
> precise definitions and annotations in use at a particular time. This
> is important, for example, for long-term access to legacy metadata; for
> developers who need fixed targets for software contracts (perhaps for
> hard-coding a given set of elements into an application, as in Ren's
> example); or for linking a namespace translation (e.g., the Dublin Core
> in Japanese) to the specific historical English version on which it is
> based.
>
> Fuzzy persistence. The semantic differences between successive
> versions of metadata terms are generally not very significant in
> practice (as Sigge has pointed out with respect to Title in DCMES 1.0
> and 1.1). Such differences do not seem important enough to justify the
> extra burden that a proliferation of unique identifiers puts on
> application developers and implementors -- for example, to crosswalk
> multiple versions of an element (e.g., Title 1.0 and 1.1) for
> searching. In fact, wherever the semantic differences really are
> significant, I assert that we are _by definition_ looking at a new
> term, not a "version" of an existing one. Practically speaking, we
> tolerate a certain measure of semantic drift in natural languages and
> we should be able to tolerate this for elements and qualifiers as
> well.
>
> One way to meet these seemingly contradictory requirements would be to
> represent vocabularies by two types of unique and persistent
> identifiers:
>
> -- by a generic identifier that never changes,
> e.g., http://dublincore.org/elements/dcq#foo (or
> http://purl.org/dc/elements/dcq#foo), [1] and
>
> -- by version-specific identifiers that would be superseded
> whenever any change in status or definition warranted a
> change of "version", as in the sequence:
> http://purl.org/dc/2000/03/13-dcq#foo
> http://purl.org/dc/2001/05/02-dcq#foo
> http://purl.org/dc/2004/01/24-dcq#foo. [2]
>
> The generic identifier would always point to the version-specific
> identifier of the most recent version. The expectation would be that
> most implementors would use the generic identifier in their instance
> metadata but that a few would use the version-specific identifier
> (perhaps redundantly) for added precision when needed.
>
I don't buy into that....
> Offering two identifiers is what W3C does with its specifications,
> allowing one to cite either the "latest version" of RDF Schema
Versions of specifications under development is one thing. Namespaces is a different game.
>or a
> particular draft, depending on need. This solution would do the same
> with vocabularies.
>
> NOTES
>
> [1] Or http://purl.org/dc/qualifiers... -- I do not much care, as long
> as we have a place to put new non-core elements such as Audience, if
> necessary.
>
> [2] A system with http://dublincore.org/elements/dcq#foo (generic) and
> http://dublincore.org/elements/dcq#foo-20000124 (version-specific)
> might achieve the same result.
>
> _______________________________________________________________________________
> Dr. Thomas Baker [log in to unmask]
> GMD Library
> Schloss Birlinghoven +49-2241-14-2352
> 53754 Sankt Augustin, Germany fax +49-2241-14-2619
>
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