In sca-core.xsd, base complex types should be abstract

In sca-core.xsd, abstract base complex types should be marked abstract.

I will raise that issue to the OSOA spec workgroup.

<complexType name="Interface"/>
should be changed to:
<complexType name="Interface" abstract="true"/>

<complexType name="Implementation"/>
should be changed to:
<complexType name="Implementation" abstract="true"/>

<complexType name="Binding">
should be changed to:
<complexType name="Binding" abstract="true">