Yes. See http://www.w3.org/TR/xmlschema-0/#SchemaInMultDocs

I think this is not possible. If I understand correctly, you are referring to schema, not idref in one xml document referring to id defined in another document. The schema would define the fact that two attribute (say cid and cidref) have to be interpreted as key and keyref, but not the actual values.

---------------------------------------------------------- Gregor Hagedorn (G.Hagedorn@bba.de) Institute for Plant Virology, Microbiology, and Biosafety Federal Research Center for Agriculture and Forestry (BBA) Koenigin-Luise-Str. 19 Tel: +49-30-8304-2220 14195 Berlin, Germany Fax: +49-30-8304-2203

Often wrong but never in doubt!