- From: Jeni Tennison <jeni@jenitennison.com>
- Date: Fri, 9 Nov 2001 11:11:21 +0000
- To: "Dave Carlson" <dcarlson@ontogenics.com>
- CC: "Mark Feblowitz" <mfeblowitz@frictionless.com>, "Xmlschema-Dev (E-mail)" <xmlschema-dev@w3.org>
Hi Dave, > The schema specification states that extension is always required to > *append* derived content to the base type, with a brief statement > that this makes it easier to test conformance of any specializations > against the base type definition. > > If you interpret this such that the derived type is validated as the > <all> group from the base type, followed by the <all> group from the > derived type, then your example should be valid. As you state, when you extend a type (and neither the original type nor the extensions are empty), the content type of the new type is a sequence of the particle from the base type followed by the particle from the derived type. So you get a sequence of two all groups. But consider the all groups in the sequence. I think that they need to meet "Schema Component Constraint: All Group Limited" from http://www.w3.org/TR/xmlschema-1/#coss-modelGroup, which states: When a model group has {compositor} all all of the following must be true: 1 one of the following must be true: 1.1 It appears as the model group of a model group definition. 1.2 It appears in a particle with {min occurs}={max occurs}=1, and that particle must be part of a pair which constitutes the {content type} of a complex type definition. 2 The {max occurs} of all the particles in the {particles} of the group must be 0 or 1. I don't think they meet 1.1 (because they're not in model group definition) and they aren't the content type of a complex type definition, because they're part of a sequence. Therefore I think it's *not* valid to extend an all with an all. (I had to think for a while about why XML Schema allows you to have an extension that contains an all group, but of course it's because the base type could be empty [just attributes].) I think we could do with some clarification. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/
Received on Friday, 9 November 2001 06:11:31 UTC