RE: intertwined specs

["Simon St.Laurent" <simonstl@simonstl.com>]

At 01:09 PM 2/16/01 -0500, Jonathan.Robie@SoftwareAG-USA.com wrote:
>1. XPath and XQuery will be using a common data model for XML
>2. This data model will be able to express XML documents that are well 
>formed, use DTDs, or have schemas.
>3. A formal algebra will be defined on this data model, and XQuery will be 
>defined in terms of this algebra. The algebra will be hard to read, but it 
>ensures that the language is well defined and well typed, so the other 
>documents, eg the language specification and tutorials, become unambiguous 
>and easier to read.

Does the data model fit XPath as it currently exists?  Or will XPath need 
retrofitting?  Does the data model play nicely with the Infoset and DOM, 
which both have slightly different views than XPath?

Does it seem odd that asking these questions on a public list is a far more 
efficient means of getting an answer to these questions than dredging the 
specs?

>In the long run, I think that the Schema Formalization effort, based on 
>the earlier MSL work (), is a key player in allowing the data model and 
>algebra to be defined in terms of Schema types.
>
>So what is the problem?

For one, MSL isn't published.  For two, MSL is an after-the-fact fitting of 
formalisms to an ad hoc spec which hasn't received rave reviews for clean 
and consistent implementation.

> > Once, long ago, I wanted the W3C to make sure its
> > specs coordinated and made some kind of coherent
> > sense.  That never really happened, but now we
> > seem to moving toward a jungle of intertwined specs,
> > with complexity increasing despite/because of reuse.
>
>Well, I'm not sure that reuse really does increase complexity. Wouldn't it 
>be more complex and confusing if each specification used a different data 
>model and type system, or if path expressions had different meanings in 
>XPath and in XQuery?

I'm not suggesting that XML Query ignore XPath, given XPath's current use 
as an ad hoc query language.  I'm not sure that using XPath inside of XML 
Schemas for keys was an especially clear-headed move, however.  I'm also 
not sure that requiring XSLT and XPath to understand XML Schemas data types 
is going to be much fun for developers who value modular code or JAR files 
of less than 1MB.

Finally, I'd suggest that the regular expressions language which is 
currently part of XML Schemas be pulled from that spec much as XPath was 
pulled from XSLT, and given a separate publication for easier reuse.  Right 
now it looks like XML Schemas depends on XPath which will depend on XML 
Schemas - not exactly a friendly foundation for development.

>Or is your concern that the type system of XML Schema adds complexity to 
>the rest of the W3C standards that support it? Are you saying that other 
>W3C specs should not support schema?

I'd suggest that W3C specs provide hooks for various schema languages - as 
the DOM working group appears to be doing 
(http://www.w3.org/TR/DOM-Level-3-CMLS/content-models.html) - rather than 
bind itself tightly to a rather controversial schema specification.

Finding people outside of the W3C XML Schema Working Group who really 
genuinely like XML Schemas is extremely difficult, in my experience.  That 
used to apply only to the Structures side, but I'm hearing more murmurings 
about Datatypes now as developers really get into it.

>Please give some examples where XQuery seems too complex to you because of 
>its support for XML Schema types.

Given the approach XQuery is explicitly taking - based on Quilt's patchwork 
- I'm not sure that question (or any answer to it) makes sense at all.


Simon St.Laurent - Associate Editor, O'Reilly and Associates
XML Elements of Style / XML: A Primer, 2nd Ed.
XHTML: Migrating Toward XML
http://www.simonstl.com - XML essays and books