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Re: XSD Schema for svn log --xml

From: Peter N. Lundblad <peter_at_famlundblad.se>
Date: 2005-07-31 16:17:20 CEST

On Sat, 30 Jul 2005, Julian Foad wrote:

> Peter N. Lundblad wrote:
> >
> 1. Maintenance. Part of the point of having those schema and/or DTD files is
> to act as regression tests to validate our XML output. That's a benefit, not a
> hindrance. At the moment such validation is done only in an ad-hoc way when
> someone feels like it, which isn't good enough. It's time we added an
> automatic regression test for it. This could look for one or two popular
> validation tools such as "xmllint", and run it if available on the system, else
> skip the test.

This sounds like a great idea!

>
> 2. Duplication. DTDs are really very weak. I wouldn't have used them except
> that schemas weren't standardised and tools for them weren't common when I
> needed to learn one or the other a few years ago, so I never got around to

It's true that other schema languages are more expressive than XML 1.0
DTDs. The main advantage for our purposes would be the datayping (i.e.
date or number instead of string).

> The only remaining argument I can see against including schemas is that
> people working on the XML output (e.g. me, sometimes) will have to learn
> to understand schemas, or get help from someone who does, but I think
> that's quite a reasonable requirement and for most changes they won't
> need a deep understanding.
>
The problem is that XML Schemas aren't that easy to grok (I've been trying
to get through that spec some times and given up). Requiring this just to
be able to check that a date is a date is not worth it IMO.

> I am only a novice in the XML world, but the impression I get is that DTDs are
> considered old-hat.
>
And so is C by some:-) We should choose a schema language based on its
capabilities vs. its complexity to learn and all that (I know you agree
here and you don't need to reply;), just pointing out that this type of
argument is quite bogus.)

If I were to choose a schema language I'd much rather use RELAX NG
(relaxng.org), just because it is so much easier to understand and write.
There are tools to translate to both DTD and XML Schema and validators
(such as xmllint) handles it as well.

OK, we are not going to have a schema language war (we're all too old for
that:-). I don't consider changing our schema language very important. If
someone writes schemas and wants to maintain them, that's something I'll
not be objecting to.

Thanks,
//Peter

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Received on Sun Jul 31 16:17:59 2005

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