- From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
- Date: 24 Aug 2001 11:35:17 +0100
- To: Daniel Flippance <DFlippance@mpsbc.com>
- Cc: "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
Daniel Flippance <DFlippance@mpsbc.com> writes:
> We are trying to define 2 schemas, one which allows 2 options in an
> xsd:choice, and one which extends this and allows 3 options.
> If one schema defines 2 choices of elements, can this list of choices be
> extended in a deriving schema?
No. The invariant for extension is that any instance of the derived
type has an instance of the base type as a prefix. Extending always
operates to allow the _addition_ of material.
To get the effect you want, use a substitution group, e.g.
<xsd:complexType name="Contact">
<xsd:complexContent>
<xsd:sequence>
<xsd:element ref="contact"/>
</xsd:sequence>
</xsd:complexContent>
</xsd:complexType>
<xsd:element name="contact" abstract="true" type="xsd:string"/>
<xsd:element name="Telephone" substitionGroup="contact" />
<xsd:element name="Fax" substitionGroup="contact" />
Then a derived schema can add
<xsd:element name="EMail" substitionGroup="contact" />
ht
--
Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
W3C Fellow 1999--2001, part-time member of W3C Team
2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
URL: http://www.ltg.ed.ac.uk/~ht/
Received on Friday, 24 August 2001 06:34:55 UTC