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Re: UKUUG Website query

From: Jukka K. Korpela <jkorpela@cs.tut.fi>
Date: Sun, 4 Jan 2004 10:33:16 +0200 (EET)
To: www-validator@w3.org
Message-ID: <Pine.GSO.4.58.0401041016510.4521@korppi.cs.tut.fi>

On Sun, 4 Jan 2004, Ian Hickson wrote:

> Why is conformance-to-a-subset-of-the-conformance-requirements-that-
> happens-to-be-describable-using-a-particular-schema-language a concept
> that needs its own term?

"Schema language"? This is about DTDs, not schemas.

The concept had a term before HTML was invented. It is a relevant concept
because such conformance can be objectively and automatically verified by
a validating parser, such as a separate validator. This is all that
validators are about, so if the concept is irrelevant, so are validators,
and this list.

> It seems to me that by making such a fuss over conformance to that subset
> you are diluting the point of conformance to the whole specification.

Au contraire. I often try to explain why validation is much less important
than many people and even organizations claim. And yes, I _am_ especially
referring to the statement "To show your readers that you have taken the
care to create an interoperable Web page, you may display this icon - -".
See also http://www.cs.tut.fi/~jkorpela/html/validation.html

> The funniest thing is that using your definition, the following:
>
>    <a><a>test</a></a>
>
> ...is invalid in HTML4, but valid in XHTML1,

You don't need my definition for it. It is a simple fact - though we don't
see such facts mentioned very often, since they reveal a little bit of the
true nature of XML as much less powerful than SGML.

> even though the _only_ reason
> for this difference is a limitation of the schema language used for XHTML.
> (XML DTDs don't support inclusions and exclusions).

In another words, and somewhat more correctly, the difference is that the
XML metalanguage does not let us specify all the syntactic restrictions
that can be described in the SGML metalanguage. And syntactic rules
written in a formalized metalanguage are what validation is about.

The word "validation" was perhaps poorly chosen, as is much of SGML
terminology. (Think about "element".) But changing that now would just
lead to more confusion. And XML keeps adding to the poor terminology,
and keeps using terms like "valid". It wasn't much of a problem when
only experts had to deal with such words. An expert knows that in data
processing, no term should be assumed to be understandable on the basis of
everyday language. But when validation has been advocated to everyone and
his dog, often with grossly false claims about its impact, confusion and
misunderstandings have been caused - people even think they know what
"validation" means without having ever read its definition!

-- 
Jukka "Yucca" Korpela, http://www.cs.tut.fi/~jkorpela/
Received on Sunday, 4 January 2004 03:33:19 GMT

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