Lost in the Namespaces whirlwind
10:12, 20 May 2000 UTC | Eric van der Vlist

Inside the increasing tornado of messages spinning in unpredictable directions on both XML-DEV and, we try and take a step backward and extricate the core facts and issues from the debate.

The discussion is clouded with the tangling of three different layers of discussion:

At a higher level, there is the semantic web vision advocated by Tim Berners-Lee: "the crucial thing is to recognize that the namespace identifier identifies the language of the message and so indirectly its meaning". This is opposed to a single focused view of the usage of namespaces strictly conforming to the Namespace Recommendation, as voiced by Jonathan Robie: "to me, namespaces are used to disambiguate names, and are used in the process of tokenizing".

The next level is a debate around the legitimacy of using namespace URIs as pointers to XML Schemas, and an underlying assumption that XML semantics should be carried exclusively through schemas. This option, already used by Microsoft tools is not endorsed by the Schema WG, and David Cleary said:

The Schema WG is not advocating that schemas be pointed to by namespace URIs. That is what the SchemaLocation attribute is for. Do not confuse the opinions of some as the consensus of the Schema WG.

The lower level is about the usage of relative URIs, and is the starting point of the discussion--it would be a purely theoretical point without the assumption than namespaces could be used as pointers. The issue is not new and James Clark gave evidence of similar debates back in 1998 when namespaces where still a Working Draft.

Several posts have proposed possible solutions to get out of this loop:

Simon St.Laurent proposed a "status quo" respecting a strict reading of the recommendation together with some flexibility around namespace URIs usage: "by my reading, relative URIs are permitted in XML namespaces, but namespaces will be compared as strings - character for character - not as converted to absolutes. Applications that want to go on from there could resolve and dereference the URI on their own recognizance, retrieving a schema, a package, a list of lightbulb jokes."

David Cleary proposed to separate the URIs from the schema binding: "attributes of the form xmlns-binding:namespace-prefix="associated-uri-reference" would be taken as declaring that the associated-uri-reference was associate with the namespace signified by the previously declared namespace-prefix."

Meanwhile, Tim Berners-Lee and others stick to the proposal of "absolutizing" the URIs: "there is a body of thought that absolutizing is right. And some code. And some specs. The same applied to literal comparison. The difference is that is we settle for URIs not being URIs, then RDF comes down like a house of cards, wheras if we go for absolutization then we probably don't have any real documents which fail."

The previous transition plan proposed by Berners-Lee got a cool reception from the xml-uri list: "we are still (in the early stages of) opening doors on the problem and its implications. After such unprecedented action as opening the xml-uri list for public discussion, the W3C hierarchy surely is not ready to go so soon for a quick solution along the path of (perceived) least resistance; is it?". One may, as did Joe Kesselman, wonder how this will end up: "is there any process by which we'll decide that this list has reached closure, or failed to do so?"

xmlhack: developer news from the XML community

Front page | Search | Find XML jobs

Related categories