JW11: single scope

If I remember correctly, we deliberately decided to limit the
scope list to one element for the first version to avoid defining and
debating
three valued elimination -- the obvious straightforward extension
of three valued logic used in other industry standards to handle
cross-repository queries. That is necessary, because the query
schemas of multiple repositories don't have to be identical, and
the issue of handling queries that are partially defined arises immediately.
First issue: Do you want your query to be defined on the intersection
of the query schemas, or their union? That must be specified.
The intersection may be too small to be useful, especially for
repositories that don't implement QSD. The union case must
obviously handle queries that are only partially defined on its
constituent repositories.

We decided to postpone this to phase 2.

Alan Babich