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Hi Henry,
Henry S. Thompson wrote:
> Robin Berjon writes:
>> * 85% of XML Schema is thoroughly useless and without value;
>
> Wow! Please identify the 15% you used -- there are lots of people
> interested in profiling XML Schema, your input would help.
I could identify the parts I used (elements, attributes, data types) and
the parts I was forced to use (complex types, the small subset you can't
get around) and while that would probably not amount to even 15% of the
text in part 1, it would not be very useful feedback for the profiling
you mention.
To be perfectly honest regarding the feature-set of XML Schema, I am
told and can observe myself very regularly that people are using it to
map XML to databases, map XML to object systems, etc. and I find that
wonderful. Few specs get to have people do so many things with them, and
that should be celebrated.
Me, I'm mostly interested in validating XML documents, or rather in the
ability to use a schema to describe as many aspects of its instances as
possible. And there are many aspects to a document. And, still being
honest, I'm still waiting for the W3C spec to do that.
I don't want the features in there I don't need to go away. If people
are using them, they definitely need to stay. I do however want them out
of my sight, because I really don't want to have to deal with them if I
implement a schema processor. Also, I don't particularly want the
features I feel I missing to go into a monolithic XML Schema 2.0 spec
because I don't think that adding to the current weight is going to do
any good.
All I'm, at heart, asking for, is modularization. Cut it up into small
manageable pieces, just like XML Schema was cut in two, but more so. And
then we can add all sorts of small modules of interest to various
communities. I understand the draw to have the One Schema Spec To
Describe All XML, but that's just not possible. Admitting defeat on that
front would be victory. The logic of interoperability seems to demand
one spec, but there are cases in which it simply won't work out.
I can't believe how much heat the binary XML people are getting with
people saying that a generic solution can't be found there without any
of those people bringing any proof of that to the table, while no one
seems to notice that in a schema language, something as fundamemental as
local determinism makes it useless to people like me, and the lack
thereof makes it useless to others :)
I think the DSDL effort gets it right by cutting things into smaller
bits. Whether it's the right way to cut things up is a topic for
discussion, but I really don't see how else we can go about this.
There is a need for an interop spec, and that can remain the XML Schema
spec, including a number of modules by reference. But users just need to
pick the parts that are of use to them. Otherwise everyone will just be
using their own 15%, and the squirrels will come back.
>> * the few useful features are weak and without honour;
>
> That seems harsh -- could you be a bit more specific? Take content
> models (I presume they're useful) -- what's weak and without honour
> about reconstructing sequence and choice, optionality and iteration,
> from DTDs into XML notation?
It is harsh, as any Klingon quote would be. You bring up notation and
it's definitely a part of it. At a very simple level, the descriptive
power to number of characters ratio just got lost between two keys on my
keyboard. But I guess everyone but me and the three other people
complaining uses IDEs and never sees the XML so it probably doesn't matter.
On another level, I've created this cool vocabulary with which I'm doing
really cool stuff on the Web. I want a schema for it because validation
is good practice. Is there one single good reason why I should know what
"deterministic content model" means, or even hear that sentence uttered
if only once?
>> * creating a modularized XML Schema is easier than with DTDs, but
>> nowhere near as simple as with RNG;
>
> Where does the difficulty lie -- notation or substance?
Allow me to answer with a question: where in XML Schema is NVDL?
>> * tools like XML Spy that are supposed to help one write schemata will
>> produce very obviously wrong instances, meanwhile the syntax of XML
>> Schema was obviously produced by someone who grew up at the bottom of
>> a deep well in the middle of a dark, wasteful moor where he was
>> tortured daily by abusive giant squirrels and wishes to share his
>> pain with the world;
>
> That's me (although _my_ moor was very conservative, not wasteful at
> all :-)
A thatcherian moor? I had no idea, I am ever so sorry :)
>> * the resulting schema is mostly useless anyway as there is no tool
>> available that will process it correctly.
>
> Really? Xerces, .NET, saxon, XSV don't count?
I should have dated the post more explicitly, it was about SVG 1.1,
which came out two years ago. Things are now better (though nowhere near
perfect). Nevertheless the amount of time it is still taking to get
reliable interoperability between implementations of a spec that has had
solid vendor support as few others have is an indication that something
is wrong with the spec. I don't pretend to know exactly where, but I'm
thinking the size and complexity of the spec don't help, especially when
most people just exercize small parts of it. I'm pushing the notion of
modularization (as others have before me) because I really think it's
the only way of making this manageable.
I know my post was harsh, it wasn't personal but it certainly was deeply
heartfelt. I work for a company that uses XML Schema intensively, most
of the time other people's schemata. I've spent literally months of my
lifetime fixing schemata that "work in XML Spy" or "work in Xerces" but
simply weren't compliant at very simple level. Now that the tools are
better it's more about handling impossibly weird constructs that the
spec tolerates and obviously natural ones that it doesn't. Whenever I
open an XML Schema document, I twitch violently until I see
elementFormDefault="qualified" (and then I drool a bit, but that's
mostly for effect). Yes it's made me bitter at 28, and yes I see
xsi:type attributes attack me in my sleep, and yes RelaxNG has had none
of these side-effects.
So please cut it down into small pieces that we can handle. *Please*
I like you comparison with Java, having had a similar experience. I'm
personally expecting to start finding it usable in three or four
iterations. I'd just like that to happen several years earlier with XML
Schema :)
--
Robin Berjon
Senior Research Scientist
Expway, http://expway.com/
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