Describing the DataContractSerializers support for import msdn has this to say:
Supported. DataContractSerializer supports xs:include and xs:import. However, Svcutil.exe restricts following xs:include/@schemaLocation and xs:import/@location references when metadata is loaded from a local file. The list of schema files must be passed through an out-of-band mechanism and not through include in this case; included schema documents are ignored.
What does "out-of-band mechanism" mean? There seems to be no other mention of this in the document.