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> From: Code for Libraries [mailto:[log in to unmask]] On Behalf Of > Ray Denenberg, Library of Congress > Sent: Wednesday, April 01, 2009 12:55 PM > To: [log in to unmask] > Subject: Re: [CODE4LIB] resolution and identification > > A concrete example. > > The MODS schema, version 3.3, has an info identifier, for SRU purposes: > > info:srw/schema/1/mods-v3.3 > > So in an SRU request you can say" > > recordSchema=info:srw/schema/1/mods-v3.3 Yes, but you can use any token for a recordSchema so long as everyone agrees that the token represents the schema for MODS 3.3. You could have just as well used an HTTP URI for that parameter in SRU which is what I typically do for things like SKOS. > Now in contrast, the schema is at > http://www.loc.gov/standards/mods/v3/mods-3-3.xsd This could have been used in place of the info URI for the SRU. This URI is a Web Document and probably is the definitive URI for version 3.3 of the MODS XML schema. > And it's also at: > http://www.loc.gov/mods/v3/mods-3-3.xsd This is a URI alias. The Architecure of the Web warns us not to create URI aliases, but HTTP allows use to do two things with this URI: 1) redirect it to the correct URI or use the Content-Location header to indicate that it is a URI alias. Neither of which is done by the LC Web site. > And also: > http://www.loc.gov/mods/mods.xsd > > And: > http://www.loc.gov/standards/mods/mods.xsd These are not the same URI as previous URIs. These URIs is to the latest MODS XML schema document. It's semantics are that of the "current" version of the schema. One of these is another URI alias that has the same issues as I previously stated. > And: > http://www.loc.gov/standards/mods/v3/mods.xsd This URI is not the same as URI as previous URIs. This URI is to the latest MODS version 3 XML schema document. It's semantics are that of the "current" version 3 of the schema. > So there you have five http "identifiers" for the schema. At this point in time all five of these HTTP URIs my dereference to the Web Document, but overtime the latter three will not represent version 3.3 of the MODS XML schema. The first URI is most likely the definitive URI for version 3.3 of the MODS XML schema. Organization need to have a clear understanding of what they are minting URIs for. Andy.