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Re: Circular types in XML Schemas

From: Jeni Tennison <jeni@jenitennison.com>
Date: Wed, 1 May 2002 18:53:50 +0100
Message-ID: <44810183722.20020501185350@jenitennison.com>
To: "Morris Matsa" <mmatsa@us.ibm.com>
CC: Yuri de Wit <yuri.dewit@metaserver.com>, "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
Hi Morris,

> I believe that necessarily infinitely recursive unsatisfiable types
> are forbidden in Schemas. This question was answered about a year
> ago on this list [1], and the part of the schema spec quoted then
> was [2]. Please tell me if I'm wrong.

Hmm... I don't think that the definition of an emptiable group
(http://www.w3.org/TR/xmlschema-1/#cos-group-emptiable) relates to the
question of infinitely recursive unsatisfiable types. As far as I can
tell, the only places in which this Schema Component Constraint is
used is when assessing whether it's OK to derive one type from another
type, and whether an element's default/fixed value is OK.

There might be something else specifying a constraint like this
somewhere, of course, but I don't think that's it. If there were such
a constraint, I guess it would be a constraint on model groups that
stated that a model group whose minimum effective total range is more
than 0 cannot contain an element particle at any level whose minimum
effective total range is more than 0 and whose type's content involves
that model group at any level. But I can't see such a constraint



Jeni Tennison
Received on Wednesday, 1 May 2002 13:53:56 UTC

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