[xsd-users] polymorphism through xs:choice

[Harg Tholan]

Hi,

I have a major doubt regard the use of *idref*.

I have an xs:choice (with maxOccurs=unbounded) of different elements which
types are derived from the same base type, then I have references to such
elements in another point of the schema. The question is, how can I
retrieve the actual type of the referenced element? I need to know the
actual type because I need to "dynamic cast" to it, but I can not know
beforehand. It seems that the use of xs:choice for achieving polymorphism
is an anti-pattern, according to this article here:
http://www.ibm.com/developerworks/xml/library/ws-tip-xsdchoice/index.html

But still, I wonder whether it could be possible to achieve this with XSD
Codesynthesis.

Code snippets:

base type:

<xs:complexType name="Base" abstract="true">

  <xs:sequence>

    <xs:element name="alive" type="xs:boolean" default="true" />

  </xs:sequence>

  <xs:attribute name="id" type="xs:ID" use="required"/>

</xs:complexType>


Then the derived types:

 <xs:complexType name="DerivedA">

  <xs:complexContent>

  <xs:extension base="Feature">

    <xs:sequence>

      <xs:element name="name" type="xs:string" />

    </xs:sequence>

  </xs:extension>

  </xs:complexContent>

</xs:complexType>



<xs:complexType name="DerivedB">

[...]

</xs:complexType>

 As said, a sequence of choice of derived types:

 <xs:sequence>

  <xs:choice maxOccurs="unbounded">

    <xs:element name="foo" type="DerivedA" />

    <xs:element name="bar" type="DerivedB" />

  </xs:choice>

</xs:sequence>

Thanks.