Correct.
> 2) DCDs use XML to describe that which you would use DTDs for (?)
Yes. (XSchema, too.)
There are a two major advantages to using XML syntax for schema information
rather than DTDs. The first is the availability of tools -- while there are
plenty of tools around for manipulating XML files, there are few available for
manipulating DTDs.
The second advantage is extensibility. Because of the stated goal that XML be
compatible with SGML, XML DTDs are (in theory) extensible only if the same
extension is simultaneously made to SGML DTDs. This makes it difficult to add a
lot of interesting schema information, such as data types, to XML DTDs. Because
there is no such requirement when schema information is represented in XML, the
field is open.
The only drawback (besides short-term availability) is if your application
requires a DTD. This is not always the case, as it is often possible to
separate authoring (which validates against schema information) from use (which
assumes validity). And even if your application requires a DTD, you might be
able to convert part of your schema information into DTD form while still using
the additional XML-based schema information (such as data types) in your
authoring tools.
-- Ron Bourret