[XSD] derivation by restriction

[Lars Geldner]

Hello,

I'm searching for a possibility to define a complex type using xml
schema that can only be derived by restriction. The sub-complex type
should have a content model that only contains elements which have types
that are subsets of the element types in the super-complex type.
For example:

<xs:element name="A" type="A_Type" abstract="true"/>
<xs:element name="B" type="B_Type" abstract="true"/>
<xs:complexType name="A_Type">
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:element ref="A" minOccurs="0" maxOccurs="unbounded"/>
<xs:element ref="B" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="B_Type"/>

Elements A and B can appear in any order.

Now I want to derive "A_Type" to such an extent that the sub-type
defines only elements that are members of the same substitutionGroup
like A and B and appear in a special order:

<xs:complexType name="a_A_Type">
<xs:complexContent>
<xs:extension base="A_Type">
<xs:sequence>
<xs:element ref="a_B" minOccurs="1" maxOccurs="unbounded"/>
<xs:element ref="a_A" minOccurs="1" maxOccurs="unbounded"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="a_B" type="B_Type" substitutionGroup="B"/>
<xs:element name="a_A" type="A_Type" substitutionGroup="A"/>

My parser says:
Ambiguous content model in the effective content model of complexType
A_Type: the following particles overlap:
<xs:element maxOccurs="unbounded" minOccurs="0" ref="A"/>,
<xs:element maxOccurs="unbounded" minOccurs="0" ref="a_A"/>
because the two particles are members of the same substitution Group.

I'm searching for a construct that has the same task like a interface in
Java.

TIA,

Lars Geldner

 

[Lars Geldner]

Lars Geldner wrote on 27.12.2004 17:58:
[...]

<xs:extension base="A_Type">

[...]

my fault: xs:extension is wrong, I want to use xs:restriction!

 

[Stan Kitsis [MSFT]]

Hi Lars,

You can restrict the usage of the derivations using "block" attribute.
Below is an example of using "block" attribute with a base type to control
type substitution in the instance document (it allows types derived by
restriction and prohibits types derived by extension).

<xs:complexType name="base" block="extension" abstract="true">
<xs:sequence>
<xs:element name="foo" type="xs:integer" maxOccurs="unbounded" />
</xs:sequence>
</xs:complexType>

<xs:complexType name="child-x">
<xs:complexContent>
<xs:extension base="base">
<xs:sequence>
<xs:element name="bar" type="xs:string" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<xs:complexType name="child-r">
<xs:complexContent>
<xs:restriction base="base">
<xs:sequence>
<xs:element name="foo" type="xs:integer" maxOccurs="1" />
</xs:sequence>
</xs:restriction>
</xs:complexContent>
</xs:complexType>

<xs:element name="top" type="base" />

As you can see above, I've defined a base class "base" and derived two
children from it - one by extension (child-x) and one by restriction
(child-r). The definition of the "top" element specifies it as of type
"base". Type "base", in turn, blocks derivation by extension. So in my
instance document I can use "child-r" (the following is valid):
<top xsi:type="child-r">
<foo>23</foo>
</top>

but not "child-x" (the following is invalid):
<top xsi:type="child-x">
<foo>23</foo>
<bar>asdf</bar>
</top>

--
Stan Kitsis
Program Manager, XML Technologies
Microsoft Corporation

This posting is provided "AS IS" with no warranties, and confers no rights.
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[Lars Geldner]

Stan Kitsis [MSFT] wrote on 28.12.2004 00:27:
[...]

You can restrict the usage of the derivations using "block" attribute.

[...]

Hi Stan,

the usage of the block-attribute is clear to me.
But what is the reason that the definded content model is ambigous? How
can I restrict a complex type if the element types of the sub-type are a
derivation (and in the same substitution group) like the element types
of the super-complex type?

 

[Henry S. Thompson]

Once you replace 'extension' with 'restriction', your schema is fine.
What parser is complaining about it?

ht
--
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: (e-mail address removed)
URL: http://www.ltg.ed.ac.uk/~ht/
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