XML trade off 1 - DTD vs XML Schema

Joshua E. Smith jesmith at kaon.com
Wed Jul 21 17:42:02 BST 1999


DTDs are far superior to the incredibly bloated form the XML Schema seems
to be turning into.  Although you *do* have to go learn a little BNF to
understand them, I challenge anyone to translate an XML Schema to a mental
model without the aid of either paper or machine.  It'd take less time to
just learn BNF.

Of course, DTDs have some problems, each of which stikes me as something
which can be easily rectified in ways which would allow old DTDs to conform
to the new spec:

add namespace support
add user-defined types (INTEGER="[-][0123456789]+")
add SGML's & so I can be more specific about my content model
let me mix PCDATA and other elements in something other than |

Maybe there are one or two other things, but just a few small changes like
that and XML Schema would suddenly be a lot less interesting.

Seems odd to me that they are going in such a radically different direction
over at W3C when DTDs are *so close* to being the right solution.

(Yeah, yeah, I know that DTDs cannot represent big nasty object models with
inheritance and whatnot, but why not just translate an existing standard
into XML syntax for that purpose?)

-Joshua Smith

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