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Re: Controlled Intermixing of Namespaced Element Types

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Fri, 25 Mar 2005 10:10:21 +0000
To: Eliot Kimber <ekimber@innodata-isogen.com>
Cc: xml-schema-dev <xmlschema-dev@w3.org>
Message-ID: <f5bu0n0m3xu.fsf@erasmus.inf.ed.ac.uk>

Eliot Kimber <ekimber@innodata-isogen.com> writes:

> OK. I'm not sure why Henry put the cell type into a separate schema, but
> in any case I was able to create a simple working example following his
> model, except in my case it is the cell element that gets substituted
> (since having a lower-level content element just adds an unnecessary
> level of containment [but see below]).

I was responding to your requirement that the users' cell fill-ins be
in a different namespace -- with hindsight it was overkill, I agree.

> But my solution should be functionally equivalent [to parameter
> entities]


> *if* processing is based on the underlying type and not on the
> element type name, in which case there is no ambiguity about the
> semantic of the substituted cell element. If processing may be based
> only on the element type name then the extra level of containment is
> required so that the cell element type name is invariant (and thus
> generalized table processors will reliably recognize the element as
> being a table cell). Hmmm.

Well, that's up to your processor, not XML Schema -- see Michael Kay's
reply to the effect that yes, it's now (XPath 2.0 and friends) easy to
select on type. . .

Wrt you element/type issue, I find it helpful to think of a lot of
document design in terms of what I call relation normal form in [1]
(or see Edinburgh normal form in [2]), in which from the domain
semantics perspective elements and attributes encode relations and
types encode (classes of) entities.

So it's a domain-empirical question whether the same class of entity
is the value of one or many relations.

Hope this helps,


[1] http://www.ltg.ed.ac.uk/~ht/normalForms.html
[2] http://www.idealliance.org/papers/extreme03/html/2003/Thompson01/EML2003Thompson01.html
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                     Half-time member of W3C Team
    2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
            Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                   URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Friday, 25 March 2005 10:10:32 UTC

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