Re: A request for some help with ambigious error messages and
On Fri, Dec 23, 2005 at 10:42:22PM -0800, thewade wrote: > 3. What exactly is a namespace if not a DTD. Because the w3c xhtml > namespace appears to be a page that itself links to a DTD and otherwise > had no code value. A namespace is a binding between a set of names and a URI. The purpose is to let software recognise when two names are the same and when they are different. This (for example) makes it possible to combine fragments of different vocabularies using (almost) cut and paste (if you add the namespace declarations) to make meaningless gibberish without conflict between names. The namespaces recommendation says nothing about DTDs or schemas of any kind, and indeed nothing about what you get if you try to defererence a namespace URI. You could think of namespaces in XML as like namespaces in C++, or qualified names in Perl, e.g. modulename::name, except that it's entirely at the syntax level, so there's not really a concept of an undefined name as there is in C++ or Perl. You can't write a DTD that understands namespaces, but you can write one that will validate if you use a particular prefix. You can even parameterise the prefix, so you have to add a declaration like <!ENTITY % prefix "xxx"> in your document (which will make many XML processors ignore the rest of your internal subset and will make Web browsers take off their shirts and run around screaming the lyrics from Hiawatha). Often it's best to avoid DTDs when namespaces are involved :( > So the first question is most important, the second two are academic. I'll answer just the third, then, since this is xml-dev :-) Best, Liam -- Liam Quin, W3C XML Activity Lead, http://www.w3.org/People/Quin/ http://www.holoweb.net/~liam/
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