Vocabulary Combination and optional namespaces
Tim Bray wrote: > Arjun Ray wrote: > >> We have it from unimpeachable authority that the Namespace mechanism >> isn't >> really for "vocabulary combination" (even though the "Motivation" section >> of the spec would seem to suggest that it might be). Thus in >> >> http://www.xml.com/pub/a/1999/01/namespaces.html >> >> it is written: "The only reason namespaces exist, once again, is to give >> elements and attributes programmer-friendly names that will be unique >> across the whole Internet." > > > Don't be silly. Why would you want names that are unique on a wide > scale if you weren't going to be combining vocabularies? > This brings up something I have run into several times in recent months, that is, the idea of an "optional namespace" when defining a vocabulary. The basic idea being that if the document is going to stand alone then no namespace qualification is needed. If it is going to be combined or contained in other vocablaries then the namespace is applied. For a concrete example consider RSS 2.0, in which the native RSS elements reside in the nil namespace: <rss version="2.0"> <channel> <title>... Which is all well and good until you try to embed RSS into another vocabulary, for example, SOAP. See  for the motivation for this: <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" <soap:Header/> <soap:Body> <rss version="2.0"> <channel> <title>... Now this could be solved by declaring an optional namespace for RSS 2.0 that could be used in just such a case: <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:rss2="http://backend.userland.com/rss/" <soap:Header/> <soap:Body> <rss2:rss version="2.0"> <rss2:channel> <rss2:title>... I have also run into such a need in other cases, for example I have worked with a group that is, at best, namespace allergic. Getting them to place the vocabulary we are working on in a namespace will be impossible. On the other hand, getting them to agree to an optional namespace to be used when combining our work other vocabularies may be palatable. What are the pros and cons of such an approach? Thanks, -joe  http://backend.userland.com/rss/  http://www.intertwingly.net/blog/1354.html -- http://BitWorking.org http://WellFormedWeb.org
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