XSD problem - variable content in foreign namespace
Hans-Juergen Rennau <[email protected]>
| Newsgroups | gmane.text.xml.devel |
|---|---|
| Message-ID | <[email protected]> |
Hello, I stumbled upon an XSD modelling problem, which is probably insolvable, but perhaps I overlook something and you might tell me. The larger topic may be summarized "Modelling elements in foreign namespaces". Here, "foreign namespace" means a namespace different from the namespace of the root element. The root element namespace I call the local namespace. Accordingly, I speak of local and foreign XSD. Now the *problem*: How to define multiple content models for an element name in a foreign namespace? In other words: how to write the XSD so that <x:foo> elements (x denoting a foreign namespace) can have different content dependent on where it appears. In the following example, <x:foo> has different content dependent on if it's a child of <b> or <c>: <a xmlns:x="http://example.com/x"> <b> <y/> <x:foo> <x:ONE/> <x:TWO/> </x:foo> </b> <c> <y/> <x:foo> <x:ONE/> <x:TEN/> </x:foo> </c></a> How to write XSD reflecting this? In general, I see two approaches how to model elements in a foreign namespace:(1) Element reference - e.g. <xs:element ref="x:foo"/>(2) Imported type - e.g. <xs:element name="foo" type="x:footype"/> Limitation of (1): the same reference QName means the same thing everywhere, so the document cannot contain <x:foo> elements with different content models, dependent on location. Limitation of (2): as the type of a complex element describes its *children*, the namespace appears in the *children* of the element with the foreign type, not the element itself. So in the example, I would have to use a type from namespace x in order to describe <x:foo>'s parent - <b> and <c>. This is possible but twisted, as it is more natural to have the type definitions for <b> and <c> in the local XSD. Even worse, it gets really cumbersome when the element in the foreign namespace has siblings in the local namespace, as is the case in the example - note the <y> sibling of <x:foo>. So one has to make a wild construction - writing into the foreign XSD types describing local elements <b> and <c>, which will have to reference local element declarations or element types (example: reference <y>), in order to achieve the mixing of namespaces. Mental ping pong. So would you agree that supporting variable content models for foreign element QNames is tricky and not straightforward at all - or do I overlook a simpler possibility? Thank you for ideas or comments!Hans-Jürgen PS: Here come the XSDs which I wrote to model the document: a.xsd:<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:x="http://example.com/x" xmlns="http://example.com/a" targetNamespace="http://example.com/a" elementFormDefault="qualified"> <xs:import namespace="http://example.com/x" schemaLocation="x.xsd"/> <xs:element name="a"> <xs:complexType> <xs:sequence> <xs:element name="b" type="x:bType"/> <xs:element name="c" type="x:cType"/> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="y" type="xs:string"/></xs:schema> x.xsd:<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:a="http://example.com/a" xmlns="http://example.com/x" targetNamespace="http://example.com/x" elementFormDefault="qualified"> <xs:import namespace="http://example.com/a" schemaLocation="a.xsd"/> <xs:complexType name="bType"> <xs:sequence> <xs:element ref="a:y"/> <xs:element name="foo"> <xs:complexType> <xs:sequence> <xs:element name="ONE"/> <xs:element name="TWO"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> <xs:complexType name="cType"> <xs:sequence> <xs:element ref="a:y"/> <xs:element name="foo"> <xs:complexType> <xs:sequence> <xs:element name="ONE"/> <xs:element name="TEN"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType></xs:schema>