- From: Ray Denenberg, Library of Congress <rden@loc.gov>
- Date: Wed, 10 Sep 2003 11:20:41 -0400
- To: <www-zig@w3.org>
From: "Mike Taylor" <mike@indexdata.com> > Just looking at the standard's specificaton of Init at > http://lcweb.loc.gov/z3950/agency/markup/04.html > and I read those familiar paragraphs: > > 3.2.1.1.7 User-information-field This parameter may be > used by the origin or target for additional > information not specified by this standard. > > 3.2.1.1.8 Other-information This parameter may be used > by the origin or target for additional information not > specified by the standard. This parameter may be used > only if version 3 is in force. > > (The same things appear in other services' PDUs) > > Can anyone remember why we have both of these, and what the > distinction between them is supposed to be? From the fact that > Other-information is only supported in v3, I suppose we can deduce > that during the gestation period for Z39.50-1995, someone wanted to do > something that, it was felt, wasn't an appropriate use for > User-information-field -- but what on earth could that be? userInformationField was defined simply as EXTERNAL. The ZIG wanted (or thought it wanted) a more all-purpose, extensible field, and came up with: OtherInformation ::= [201] IMPLICIT SEQUENCE OF SEQUENCE{ category [1] IMPLICIT InfoCategory OPTIONAL, information CHOICE{ characterInfo [2] IMPLICIT InternationalString, binaryInfo [3] IMPLICIT OCTET STRING, externallyDefinedInfo [4] IMPLICIT EXTERNAL, oid [5] IMPLICIT OBJECT IDENTIFIER}} -- InfoCategory ::= SEQUENCE{ categoryTypeId [1] IMPLICIT OBJECT IDENTIFIER OPTIONAL, categoryValue [2] IMPLICIT INTEGER} The plan was that alot of "categories" would be defined and some even registered. But that never really got off the ground. So this was a case of over-engineering. Can't use it in version 2 because it wasn't defined until the 1995 version. However, it has been retrofitted for version 2, see: http://lcweb.loc.gov/z3950/agency/defns/user-1.html --Ray
Received on Wednesday, 10 September 2003 11:20:41 UTC