I am finding the use of terminology here a little confusing. You say that Doc Book is an XML language. I would say it is a particular DTD, and a DTD is a possible way of defining the elements of a particular XML language. Alternatively, an XML language can specify its element by a Schema, or simply define its elements within each document itself. Also, one of its main features is its flexibilty compared with HTML. Each user can, indeed, define their own mark-up language by defining each required and optional element for their language. Finally, the entire Doc Book DTD has been made available by O'Reilly online, and I suggest you provide a link to it. RoseParks
Yeah, DocBook probably isn't the best example, because it can be implemented in SGML as well. I'll reword to use something better. XML is not itself a markup language; specific applications of XML (defined by a DTD or schema) are. I'm not sure of a better way to word that.
It has occured to me that one way of thinking about XML is as a specification for the encoding of information. And, as is pointed out above, is not really a language in itself in the sense that it doesn't have its own vocabulary. The RDF (Resource Description Framework) states something to the effect of letting XML handle the issues with globalization (Unicode) and data formatting through the XML element/attribute/text value syntax and through other low-level transport considerations.
In most representations of multiple levels of XML applications that I see, it starts looking a lot like the OSI Model for networks. In the same way that applications run on top of TCP or UDP which run on top of IP (I think I got the order right), the DocBook "application" or RDF or any of the zoo of XML-based languages build on top of XML or could be done in SGML, or dozens other forms of data representation.
StWeasel
- XML is really a language in itself, with its own vocabulary (made up out of < and > and other such characters and groups of characters), its own grammar, et cetera. But it is a language whose sole purpose is to describe another language, which seems to confuse people (just like with HTML); the metalanguage gets mistaken for the languages it describes.
- What is stated above is that XML in itself is not a mark-up language, and that is true.--branko
While it might be arguable that it has a vocabulary, I can definitely agree on the characterization of XML as a metalanguage. It seems that the distinction I draw is that XML is essentially a mere specification of a syntax (how symbols can be put together to form the primitives of a language), but depends on other specifications as extensions (XHTML, MathML, RDF and the like) to provide a semantics (what can actually be expressed and how this expression is interpreted for meaning). It seems to me very much like saying that ASCII is a language, but from certain viewpoints I can see how this would be a valid statement. -- StWeasel
Deleted following:
- The document must identify itself as an XML document with a preliminary declaration to this effect. This declaration is known as a prolog. It will contain information about the XML version and possibly also information about encoding and whether the XML file is standalone or not.
Read the spec, and see how above is false.
SHould we mention that Apple's OS X uses XML for most of its stored property settings (ie the equivalent of the weindows registry), the plist files? -- Tarquin 12:37 May 8, 2003 (UTC)
I removed this sentence from the article: Also, again unlike HTML, XML tags explain what the data means rather than how simply to display it. I don't see how something like this can be said about a purely syntactic specification, also eg. XHTML is a concrete example that this is misleading at best. Maybe something similar but NPOV could be put in as a statement about recommendations and best practices. -- Mp 09:31, 27 Aug 2003 (UTC)
The article shouldn't go into the details of the syntax of XML, especially when not all of it is covered. A definition of well-formedness is given that refers to elements, but "element" is never defined. I think a short example of an XML document is sufficient; anybody wanting more can read the spec. -- 64.81.99.73 20:20, 1 Sep 2003 (UTC)