xml-dev - Re: Namespaces and the Valid Document

["Steven R. Newcomb" <srn@techno.com>]

[From: "Stallion, Jason (Cahners)" <JStallion@cahners.com>]

> I foresee a time when my company will want to construct XML documents
> according to rules defined in distinct DTDs.  Namespaces will play a part in
> this.
> 
> But those documents will still need to be validated.  
> 
> The URI associated with a namespace prefix does not need to point to a DTD.
> Even if it does, there is no requirement in the recommendation that the DTD
> play any part in validation.
> 
> So how do I validate my document?  Do I need to create a new DTD that
> encompasses all of the newly-prefixed elements and attributes?  This could
> result in a need for dozens of DTDs:  a new DTD every time I aggregate
> someone else's XML document.  Or, at the very least, dozens of external
> entity files.  And the possibilities for namespaced attribute combinations
> are so numerous that constructing a content model to represent all of those
> possibilities seems a daunting proposition.
> 
> If all of this is true, what have I really gained by the use of namespaces?
> Merely protection against the (rare?) possibility of a name collision?
> Seems like a lot of overhead to avoid what could be an infrequent problem.
> 
> And if the namespace URI does point to a DTD, is there a parser that *will*
> use that DTD as an aid to validation of that part of the document?

What you are looking for is the ISO "architectural forms" paradigm.
Architectural forms provide a way to syntactically validate documents
that use multiple vocabularies, against the intrinsic syntactic
requirements of all of the "inherited" vocabularies.  (As a matter of
fact, I was just speaking about this last Sunday at the Healthcare
Information Management Systems Society Conference here in Dallas, at
the invitation of Electronic Laser Forms.)

I suggest you take a look at http://www.hytime.org/htnews.html.  There
is a link to a version of the SP parser that will validate XML
documents that contain base architecture declarations, a very simple
"hello world" type example, and some miscellaneous explanatory
materials.

Also, Chapters 9-11 of:

  Megginson, David. Structuring XML Documents. Charles F. Goldfarb
  Series on Open Information Management. [Subseries:] The Definitive
  XML Series from Charles F. Goldfarb. Upper Saddle River, NJ:
  Prentice Hall PTR, [March] 1998. Extent: xxxviii + 425 pages,
  CDROM. ISBN: 0-13-642299-3.  Price: US $39.95.

XML Namespaces are not involved in architectural forms.  Architectural
forms are simply a more sophisticated (and did I mention
internationally standardized?) way of doing multiple information
architecture inheritance in XML.

-Steve

--
Steven R. Newcomb, President, TechnoTeacher, Inc.
srn@techno.com  http://www.techno.com  ftp.techno.com

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