Re: [HACKERS] Re: [QUESTIONS] Z39.50

On Wed, 18 Jun 1997 adrian@hottub.org wrote:

.. > >
.. > >     The Z39.50 specs are at http://lcweb.loc.gov/z3950/agency/
.. >
..
.. In short, Z39.50 is the protocol WAIS servers use to dispense their
.. data.  I didn't think WAIS was as used anymore with the advent of
.. the web.
..
.. Anyhow, with libpq, it should not be that much problem to put a
.. Z39.50 interface on it.  However, that would involve a two-step
.. process (connection to the Z39.50 server and a further step for
.. the Z39.50 server to connect to PostgreSQL).
..

Z39.50 has developed a lot since the WAIS days.

Z39.50 version 3 was adopted as an ANSI standard in 1995, and also as an
ISO standard in 1996 (ISO 23950).

Z39.50 is a client-server protocol for database searches via remote
networks where the clients and servers may run on different computing
systems. It is developed to support (but not limited to) bibliographic
databases. Z39.50 does not directly support database updates, only queries
(searches).

Z39.50 is interesting in the way it handles searches: When a Z39.50
server performs the search, it constructs a result set consisting of
(pointers or references to) the records in the search result. The
Z39.50 client can then issue additional queries to retrieve selected
records from such result sets, and it may request these records
in different forms (e.g. full or brief with varying amounts of fields
present in each response record).

Z39.50 is intended to be a common networked DB search protocol,
independent of the underlying database system.

To support a combination of PostgreSQL and Z39.50, you must build
a Z39.50 server that uses PG as its database backend. This is a
non-trivial, but feasible task.

Z39.50 allows database queries to be submitted in different forms,
but does not (yet ?!) support SQL queries to be sent from the
client to the server. In particular joins are very hard to express.

The typical bibliographic search is done to a database (SQL people should
read this as a table). The query consists of a set of search terms
combined by logical operators (And, Or, AndNot, Prox) in Reverse Polish
Notatoin (RPN). Each term may be qualified with several attributes
determining which search key (i.e. index) to use and other attributes such
as completeness, truncation, relations, word or phrase structures.

regards
Erik Bertelsen

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