Namespaces and DTDs
richard at goon.stg.brown.edu
Wed Mar 10 13:16:35 GMT 1999
Ronald Bourret wrote:
> The only inobvious bit is that, because there is no way to declare
> namespaces in the DTD, you can't declare different default namespaces
> for different parts of the DTD
Because the DTD is not namespace aware, all it can deal with are the pre-
fixes you declare (not the URLs associated with them). Since these pre-
fixes are declared in the document content, you end up with a peculiar
situation in which the DTD has to be written according to declarations
in a given document instance, rather than the reverse. Worse yet, there
is no way to be sure that the various documents being validated against
a particular DTD use the prefixes correctly, with the correct URLs, un-
less you make extensive use of attribute defaults - which, ironically,
means we now need the DTD (probably an external one, typically with a
bunch of parameter entities; so get your validating parser ready).
After another year or two of this, with alternate schemas floating around
besides DTDs, with architectural forms, with namespaces, and what not -
after all of this, I wonder if we'll all, in good conscience, be able to
say that anything has been simplified.
(Simplicity _was_ one of XML's primary goals back in the dark ages last
In reality, XML is functioning less like a "simplification," and more like
a political move intended to facilitate changes that could never have been
made to a mature standard like SGML.
This is actually a very old story that's been repeated many times over.
(Just look at what's happened to LDAP. By the time we get all the PKI and
ACL extensions in place, it's really not going to be very L.)
In the end, LDAP and XML may end up serving their constituencies better
than their predecessors did. Or they may not. Frankly, with regard to
XML, the jury is still out. It's not catching on nearly as fast as pre-
dicted a year or two ago. And it's taking considerably more work to im-
plement it than anybody ever envisioned.
Those of us who have done the work of writing XML processing software,
and of making it work, have a right to say this.
The emperor may or may not have clothes.
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