Question about xsd:extension

[Amol]

Hi all,
I have a case where I have a element that can appear under multiple
elements
e.g.
<AppFunctions>
<UseTemplate name="1"/>
<MethodSet name="2">
<UseTemplate name="3" />
<MethodCall name="4" />
</MethodSet>
<MethodSet name="5">
<MethodCall name="6" />
</MethodSet>
<UseTemplate name="7" />
</AppFunctions>

I would like a way to define a root element which has just the
UseTemplate element and then derive 2 elements from it "AppFunctions"
and "MethodSet" which extend it to add further elements to it. This
elements in the derived elements need to unordered and can occur
multiple times. This is what I came up with:

<xs:complexType name="UIElementType">
<xs:choice maxOccurs="unbounded">
<xs:element name="UseTemplate" type="UseTemplateType" minOccurs="0"
maxOccurs="unbounded" />
</xs:choice>
</xs:complexType>

<xs:complexType name="AppFunctionType">
<xs:complexContent>
<xs:extension base="UIElementType">
<xs:choice maxOccurs="unbounded">
<xs:element name="MethodSet" type="MethodSetType"
maxOccurs="unbounded" />
</xs:choice>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<xs:complexType name="MethodSetType">
<xs:complexContent>
<xs:extension base="UIElementType">
<xs:choice maxOccurs="unbounded">
<xs:element name="MethodCall" type="MethodCallType" minOccurs="0"
maxOccurs="unbounded" />
</xs:choice>
<xs:attribute name="name" type="xs:string" use="required" />
</xs:extension>
</xs:complexContent>
</xs:complexType>

This definition is allowing me mutiple UseTemplate nodes directly under
AppFunctions but once I add a MethodSet node under AppFunctions, it
does not allow any UseTemplates anymore.

Thanx in advance,
Amol.

[George Bina]

Hi,

That is because the content type of the derived type contains a
sequence of the two choices, see 3.2.3 from
http://www.w3.org/TR/xmlschema-1/#key-efm
***
3.2.3 otherwise a pair of mixed or elementOnly (determined as per
clause 3.1.2.1 above) and a particle whose properties are as follows:

{min occurs}
1
{max occurs}
1
{term}
A model group whose {compositor} is sequence and whose {particles}
are the particle of the {content type} of the type definition
·resolved· to by the ·actual value· of the base [attribute]
followed by the ·effective content·.
***

Best Regards,
George
---------------------------------------------------------------------
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
http://www.oxygenxml.com

[Amol]

Is there any other way to get the behavior where the extension would
behave as a choice rather than sequence. The element I want to
"inherit" occurs under multiple elements so rather than define once
under each I was hoping to define it once in a parent element and
extend all the elements that need it from the parent element.

Thanx, Amol.

[George Bina]

No, In XML Schema the model created by extension is sequence.
On possible approach is to place common content in a named group and
refer to that group from your complex types where you want that common
content.
Another one that will have a behaviour very close to what you want is
to define for instance an abstract element, let's say instruction and
define the content model using references to this element. Then you can
define actual non abstract elements that can substitute instruction.
The instruction element will be basically replaced in this way with a
choice of all the elements from its substiturion group.
Have a look at the XML Schema for XSLT 2.0, there you can find
something like I described above:
http://www.w3.org/TR/xslt20/#schema-for-xslt

Best Regards,
George
---------------------------------------------------------------------
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
http://www.oxygenxml.com