W3C home > Mailing lists > Public > xmlschema-dev@w3.org > August 2005

Re: XSD feature check-lists

From: <noah_mendelsohn@us.ibm.com>
Date: Tue, 2 Aug 2005 16:49:12 -0400
To: "Pete Cordell" <petexmldev@tech-know-ware.com>
Cc: xmlschema-dev@w3.org
Message-ID: <OF4A3500B1.B1918822-ON85257051.00722A70-85257051.00725E40@lotus.com>

(sorry for slow reply--working through back emails following vacation):

Pete Cordell writes:

> I don't know whether this has been suggested
> before, but as an alternative to defining domain
> specific profiles of XSD, maybe the W3C can define
> an official, standard checklist of features that
> vendors can fill-in and display on their web
> sites.  This would give customers an equal basis
> for assessing products, and give vendors guidance
> on where they can improve their products.

I think that encouraging vendors to be honest about the status of their 
products is a good thing, but appearing to encourage subsets is not.  How 
would we feel if for XML itself we suggested a checklist along the lines 

_ do you support attributes?

_ do you support entities?

_ do you support the short form of empty tags?

_ do you handle whitespace correctly?

etc.  XML interoperability would be seriously damaged.  The point of XML 
is that you don't get a choice about these things and we don't encourage 
reporting of subsets.  We tell you not to claim you're XML-compatible 
until you do all of these things.  As a result, customers find that XML 
interoperability is pretty good.

The same concern applies to schema.  While a few vendors are still having 
particular trouble and that is causing unfortunate confusion, my 
impression is that a number of the more careful XML schema validators are 
showing quite good conformance and interoperability.  Of course, there are 
some things like data binding tools that aren't even trying to support the 
whole language, though some of the things they subset are in XML not 
schema (e.g. mixed content.)

Bottom line: while schema does have well known complexity issues, I think 
we should be very reluctant to promote ad-hoc subsetting in particular 
implementations.  I'm afraid that publishing a matrix in which you can 
document your non-conformance may appear to do just that.

If you're talking about things like databinding tools, I support what I 
took to be the consensus of the recent schema workshop:  tools should 
support all of schema and XML, but should optimize the subsets most likely 
to be heavily used and/or a good match to the environment.  A checklist to 
document such a subset may make sense, and I think that as a result of the 
workshop the W3C is considering a closer look at that area.

Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
Received on Tuesday, 2 August 2005 22:28:39 UTC

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