Proposal Critique - XML DTDs to XML docs
bckman at ix.netcom.com
Fri May 22 20:58:28 BST 1998
>>Every attempt didn't quite do everything that everybody needed, and
>>the harder people worked to make languages "extensible", the more complex
>>(C++) or merely unpopular (Lisp) the language became.
I think this is a good point and an excellent argument for Simon's proposal.
This language will be a very useful tool for a subset of users who dont want
the hassel of learning a DTD language. There are always going to be things
that a DTD is necessary for, but that doesnt mean that this is the only tool
one should use.
On the other hand if a language tries to be something to every one it is in
danger of becoming like a swiss army knife. It will perhaps do the job, but
not as well as a specialized tool.
From: Paul Prescod <papresco at technologist.com>
To: Xml-Dev (E-mail) <xml-dev at ic.ac.uk>
Date: Friday, May 22, 1998 2:46 PM
Subject: Re: Proposal Critique - XML DTDs to XML docs
>Simon St.Laurent wrote:
>> >Is there any good reason that the ability to change the parse tree
>> >be conflated with the responsibility for verifying schema-compliance as
>> >they are in DTDs. Is there any good reason to perpetuate this conflation
>> >in your proposed replacement for DTDs?
>> I'd like to see a structure that's:
>> a) easily interpreted, edited, and stored, without the need for multiple
>> b) capable of containing a complete set of information about a document,
>> including structure and data
>The word "structure" is too vague for me to be able to argue for or
>against. Are you talking about a single *language* (or specification) that
> a) instance syntax
> b) textual replacement
> c) external text embedding
> d) extensible validation
>XML 1.0 incorporates all of them. I think that that made sense for XML
>1.0, in order to be SGML compatible, but for future versions I would
>rather see the first three completely separate from the fourth. The reason
>I feel that the last should be separated is that the types of validation
>(or "verification") that people have to do can be quite varied. XML made
>the DTD optional for this reason. I don't see that making the XML
>specification substantially larger with an alternative encoding for DTDs
>can really make that specification simpler.
>> Why on earth would I
>> want to keep multiple sets of document descriptions (schemas, whatever)
>> that share the task of defining the same document set? It seems like a
>> management mess, a processing mess, a waste of bandwidth and storage
>> of redundant information, and just generally a nuisance.
>> Making DTDs extensible is a good way, in my view, to address this issue,
>> several others.
>That sounds attractive, and I encourage you to try and make it work. If
>you succeed, I will be happy to use it. But, to be honest, I don't think
>it will succeed. It's like in the early days of computer programming when
>people thought that it was possible to invent a single, "extensible"
>programming language (or "meta programming language") that would serve all
>needs. Every attempt didn't quite do everything that everybody needed, and
>the harder people worked to make languages "extensible", the more complex
>(C++) or merely unpopular (Lisp) the language became.
>I personally don't believe that one extensible schema/DTD language can
>serve all of our diverse validation needs. The set of "extensions" will be
>unlimited and approach the complexity of a full programming language. Look
>at RDF schemata. They are miles and miles away from DTDs. I've had
>document types where I was modeling OO systems and wanted to verify things
>like "base class is not inherited more than once." Some OO-modeling schema
>language would handle that, but DTDs (even extensible ones) could never do
>I tend to think that a strategy that is more likely to be successful is
>one that layers schema languages. At the bottom level you have something
>like XML DTDs without all of the stuff related to entities and notations
>(in XML element notation). That layer might include data type validation.
>In levels above that you have RDF and other schemata that are more
>interested in relationships than in positional occurrence.
>It seems like you are interested in that bottom layer schema. I think that
>it would be good to formalize an XML element notation for the bottom
>layer. But if you try to make it a replacement for DTDs, then it must do
>everything that DTDs do and inherit all of the problems that the
>conflation of features in DTDs causes.
>> What's so difficult about that? I can't think of any good reason
>> SGML compatibility) to oppose either of those goals.
>It is quite likely that SGML will soon be changed to allow you to use
>whatever notation you want for XML DTDs. SGML compatibility is not a
>problem. The question is what is the right design. You can make a slightly
>better version of a bad design, or you can try to start again with a good
>Let me ask this plainly:
>Does it make sense
>a) that textual substitutions should be specified in a part of a document
>called a "document type definition".
>b) that the "document type definition" should also be responsible for
>declaring media types and attaching them to non-XML entities.
>c) that the language for verifying element and attribute occurrence must
>be in the same specification (XML 1.x) as that for creating elements and
>I don't think that those three things (among others) make sense anymore.
>Hence, I don't think that inventing a new notation for this inappropriate
>concept is a good idea. If we are to replace DTDs, let us replace them
>with something simpler and more specific to the task of validation,
>instead of transliterating them into another syntax, warts and all.
>Paul Prescod - http://itrc.uwaterloo.ca/~papresco
>"A writer is also a citizen, a political animal, whether he likes it or
>not. But I do not accept that a writer has a greater obligation
>to society than a musician or a mason or a teacher. Everyone has
>a citizen's commitment." - Wole Soyinka, Africa's first Nobel Laureate
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