Xsd and multiple inheritance - xsd

Question

Sorry for such a long question. I'll try to make it as simple as it gets.
We are working on a modular computational framework. The framework reads the configuration from xml file and we would like to validate the configuration against xsd. While adding new modules, we would like the xsd to be as simple as possible in the sense of maintainability.
The structure of framework is the following (in c#):
interface IModule { ... }
interface ISource : IModule { ... }
interface IFilter : IModule { ... }
interface IProcessor : IModule { ... }
and we have abstract implementation of various module interfaces and the implementation of modules (e.g. ObjLoader : AbstractSource). The structure of xml is following:
<Test>
<Sources>
<ObjLoader .../>
</Sources>
<Filters>
...
</Filters>
<Processors>
...
</Test>
Currently to avoid the necessity to heavily modify the xsd with every new module, we have the following test.xsd:
<xs:include schemaLocation="framework.xsd"/>
<xs:include ... modules />
<!-- adding includes for every module or group
of modules is the only modification -->
<xs:element name="Test">
<xs:complexType>
<xs:sequence>
<xs:element ref="this:Sources"
minOccurs="1"
maxOccurs="1"/>
...
</xs:sequence>
</xs:complexType>
</xs:element>
and common framework.xsd:
<xs:element name="Sources">
<xs:complexType>
<xs:choice maxOccurs="unbounded">
<xs:element ref="this:AbstractSource"/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name="AbstractSource"
abstract="true"/>
<xs:complexType name="ISource">
<xs:complexContent>
<xs:extension base="this:IModule">
...
</xs:extension>
</xs:complexContent>
</xs:complexType>
...
Each module (or group of modules) has its own xsd file with its definition and this file is included in the test.xsd:
<xs:include schemaLocation="framework.xsd"/>
<xs:element name="ObjLoader"
substitutionGroup="this:AbstractSource">
<xs:complexType>
<xs:complexContent>
<xs:extension base="this:ISource">
...
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:element>
So far so good and everything works well. For each dll with modules we provide corresponding xsd and include it in test.xsd. But during the development, modules that are primarily of some kind, but can produce another operation as a side effect appeared. It is not a problem in the c# side as we can have the following class:
class GreatProcessingFilter : AbstractProcessor,
IFilter { ... }
Is there a way to modify our xsd to be able to handle such elements that can be a substitution of multiple abstract elements? Something like:
<xs:element name="GreatProcessingFilter"
substitutionGroup="AbstractProcessor"
substitutionGroup="AbstractFilter"> ...

Answer 1

XSD 1.1 does allow multiple QNames in the substitutionGroup attribute. It does not, however, cause the element declared as a member of multiple substitution groups to be given a type constructed dynamically from the types assigned to the various substitution-group heads. So it probably doesn't qualify as multiple inheritance in the sense you are looking for. You may find XML schemas with multiple inheritance of interest.
[Addition, responding to OP's comment] In XSD 1.1, a top-level element can be declared with multiple substitution groups; it can then be substituted for any of the elements named (unless blocked by the relevant final attribute on the substitution-group head). The constraints on substitution-group affiliations are as in 1.0: the type of the element being declared must be validly substitutable for the type of each substitution group head. If no type is given for the element, it defaults to having the same type as the first substitution-group head.