new (draft) version of holdings schema

A revision of the abstract schema for holdings has
been drafted, by Bill Moen and Joe Zeeman,
intended to reflect and consolidate all of the
agreements from a number of meetings culminating
in decision at the April ZIG and Bath meetings.

The draft is available at:
http://lcweb.loc.gov/z3950/agency/defns/holdings1-3.html

This is designated version 1.3. Please review, to
make sure that the decisions are accurately
reflected.

--Ray