BPDMF2 — spec doesn't provide a unified way to specify and represent link references

The specification doesn't provide a unified way to specify and represent link references. It is currently possible to use either IDREF or href. Furthermore, no standard URI representation is made mandatory. The lack of mandatory reference scheme prevents to ensure interoperability when xmi models are organized in multiple xml files.

Resolution:
A new xmi_infra.xsd schema is created to host the XML attributes to provide validation of reference in the context of XML schemas.
The LinkAttribs complex type allows either for id/IDREF references and id/href references.

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xmi="http://schema.omg.org/spec/XMI/2.1"
targetNamespace="http://schema.omg.org/spec/XMI/2.1"
>

<xsd:include schemaLocation="../../../XMI/20071213/xmi.xsd"/>

<xsd:attribute name="idref" type="xsd:IDREF"/>
<xsd:attribute name="label" type="xsd:string"/>
<xsd:attribute name="referenceTypeID" type="xsd:QName"/>

<xsd:complexType name="LinkAttribs">
<xsd:attribute ref="xmi:label" use="optional"/>
<xsd:attribute ref="xmi:idref" use="optional"/>
<xsd:attribute name="href" type="xsd:string" use="optional"/>
<xsd:attribute ref="xmi:referenceTypeID" use="optional"/>
</xsd:complexType>

</xsd:schema>