DTD Required for XSL processing?

[Corey McGlone]

Is an XML document required to have an associated DTD in order to be processed with an XSL stylesheet? Look at the example shown here, it doesn't appear that one is required. I just wanted to make sure that I'm interpreting this correctly.
Thanks,
Corey

[Scott Bain]

No, XSL does not require that the document being transformed include a constraint, neither DTD nor XML-Schema. Validation to a constraint is purely a parsing issue, and XSLT deals with your XML as a structure of objects (similar to DOM), not as XML per se.
In fact, this is one crucial thing to remember when you're first studying XSLT. Don't think tags and values, think nodes in an object tree.

[Corey McGlone]

Validation to a constraint is purely a parsing issue...

So what does a DTD really do for you? I realize that it describes the various tags and what encapsulates what and so on, but when is it used and by what? You had mentioned that it had to do with parsing - do most parsers utilize the DTD in order to do their work? In order to edit an XML document using the XML DOM, is that XML document required to have an associated DTD or XML-Schema?
By the way, what is an XML-Schema? How is it different than a DTD? I've never heard of that term before...
Corey
[ January 15, 2002: Message edited by: Corey McGlone ]

[Scott Bain]

A constraint (DTD or Schema) is a set of "the rules" about a given XML grammar. What elements are allowed, what attributes they can or must have, what sub-elements are contained within an element, etc...
Advantages:
Robustness - you check your documents against the constraint, they pass, you know they are valid and can be parsed (consumed) as you expect
Documents your intentions - If you specify that element x must contain 5 sub elements y, then someone reading the constraint knows this is a requirement, not just "it so happened" in a given XML instance.
Can establish defaults for attributes - Only in a DTD or schema can you establish default values for attributes.
Entites - you can define your own entities, like a copyright symbol for instance, in the contraint, then use the entity name in your XML document.
DTD is the older constraint system that comes to us from SGML. It is quite well established, but it itself is not written in XML (but rather in its own syntax). XML-Schema is a constraint system written in XML, so you can use all your existing XML tools to edit/validate/transform it. It has other advantages too, but is newer technology, so the support is spotty.
HTH!