RE: Alternatives to XML Schemas

[Michael Brennan <Michael_Brennan@Allegis.com>]

> From: Jeff Rafter [mailto:jeffrafter@earthlink.net]
> Sent: Tuesday, March 06, 2001 2:02 PM
> To: xml-dev@lists.xml.org
> Subject: Re: Alternatives to XML Schemas
> 
> [...]
> Am I the only one who, after learning TREX, didn't have the 
> reverberating
> thought floating in my brain, "Huh, so even TREX relies upon 
> XML Schemas..."
> after reading that XML Schemas Part 2 Datatypes is the 
> primary datatype
> implementation "...maybe relying on XML Schemas isn't so bad."

I don't think relying upon XML Schemas is inherently bad. There are many
applications of XML that require datatypes, so relying upon what's already
there and working isn't so bad. But it's fair to ask if the whole set of XML
specs is introducing too many gratuitous interdependencies and creating too
much complexity. We keep hearing the refrain "don't learn it if you don't
want to use it". When we keep introducing interdependencies, though, then
telling people "don't learn it if you don't want to use it" is really saying
"don't use XML if you want simplicity" because there are too many
interdependencies and you can no longer pick and choose what to use.

> [...]  
> If you aren't
> going to use those extra features don't learn them.

Unfortunately, there are many implementors who will heed your advice. I have
so far identified only a few implementations of XML Schema. Each is focused
on one very narrow use case (typically validation) and each supports only a
subset of the spec. Will this situation get better or worse? I hope it gets
better, but I'm not sure.

I don't think XML Schema is far from the mark, and I wouldn't agree with
those who characterize it as a failure. The task the schema WG tackled was
one inherently fraught with controversy; they couldn't have pleased
everyone. I would have preferred a bit more simplicity, though, and I share
the concerns expressed by others of a growing reliance of many XML specs on
a post-validation Infoset. Compliant XML parsers are an abundant commodity
freely available to all; compliant schema parsers (supporting generalized
application use, not just validation) are not an abundant commodity, and I
see no current evidence of that changing. The trend seems toward making XML
less accessible, both in terms of ease of use and availability of cheap
tools.