Assembling a schema for a single target namespace from multiple schema definition documents

Section 4.2.1 (http://www.w3.org/TR/xmlschema-1/#compound-schema
<BLOCKED::http://www.w3.org/TR/xmlschema-1/#compound-schema>  "Assembling a
schema for a single target namespace from multiple schema definition
documents") states: 
 
"Schema components for a single target namespace can be assembled from
several  <BLOCKED::http://www.w3.org/TR/xmlschema-1/#key-schemaDoc> .schema
documents., that is several
<BLOCKED::http://www.w3.org/TR/xmlschema-1/#element-schema> <schema> element
information items: "
 
but then goes on to elaborate on how <include>s should be treated.
 
What is not clear to me is what should be done if, during the course of
schema discovery, disjoint schema definition documents are encountered for
the same namespace. This could happen for example via chains of <import>s in
complex situations. Instinctively one would think one should take the union
of everything, and, as long as there were no inconsistencies, proceed
happily. However I am having a hard time figuring out if this is explicitly
addressed anywhere and, if so, how.
 
Any input, references etc. would be gratefully received.
 
Thanks
 
Hugh Wallis