SUMMARY: XML Validation Issues (was: several threads)

[Marc.McDonald at Design-Intelligence.com]

I would ask what is the reason for a document needing validation 
parsing. I see 3 reasons:
1.	To include entities and attribute defaults that are external to the 
document
2.	To indicate the document should match a given structure (the DTD)
3.	To describe the structure the document matches

On the second point, it can be argued that any document that declares 
its DTD met that structure when it was created. In other words, you 
don't expect such a document to fail validation. So why go through 
validation at all?

On the third point, consider the cases where a DTD can't completely 
express the constraints on the document. Or where the application that 
produced the document and the one that consumes it both implement the 
document structure in code rather than a DTD. Such an application may 
use a well-formed parser to read the document and then apply the 
constraints via explicit code.

For these reasons I would:
1.	Allow a document to indicate the structure that it meets, which can 
be a totally abstract URI and/or a DTD.
2.	Require well-formed parsers to handle attribute defaults, entities, 
and external files but not element declarations.
3.	A validating parser would add processing element declarations and 
full attribute processing.
4.	An application (the user of the parser) selects if the parser will 
validate and in fact can substitute its own selected DTD.

Marc B McDonald
Principal Software Scientist
Design Intelligence, Inc
www.design-intelligence.com


----------
From:  Simon St.Laurent [SMTP:simonstl at simonstl.com]
Sent:  Thursday, April 08, 1999 8:57 AM
To:  XML-Dev Mailing list
Subject:  Re: SUMMARY: XML Validation Issues (was: several threads)

At 08:22 AM 4/8/99 -0700, Tim Bray wrote:
>>(not to UI designers, provide two
>>separate icons for "validate" and "check wf" )
>
>Yes!  IE5 has a nice validation capability, but no way (that I've
>found) for the user to invoke it.  Is there one?

See
http://msdn.microsoft.com/downloads/samples/internet/xml/xml_validator/  
defau
lt.asp.  I don't know that it counts as 'user invocation' the way you 
meant,
though.

>Good question; I can see both sides.  But in fact, Chris, I think 
what's
>motivating you here is less a concern for forcing validation than a
>concern for forcing the use of the external DTD for entity 
declarations
>& attribute defaults and so on.  Which is fine; but I think there 
are
>2 separate questions here:
>
> - should a document be able to ask for validation
> - should a document be able to ask for guaranteed reading of all
>   external entities
>
>Related but distinct. -Tim

And that's precisely why XML Processing Description Language (XPDL) 
separates
them.  See http://purl.oclc.org/NET/xpdl for details.  It also 
provides a
mechanism for making the readability of these features optional, when
appropriate, though the default requires the resources to be read.

Simon St.Laurent
XML: A Primer
Sharing Bandwidth / Cookies
http://www.simonstl.com

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