Message-Id: <199602051712.LAA01147@library.wustl.edu> Date: Mon, 5 Feb 1996 17:02:42 +0100 From: Alan Jackson <mailto:alan_j@SUPVAX.SLS.CO.UK> Subject: Re: Search History To: Multiple recipients of list WEBCAT-L <mailto:WEBCAT-L@WUVMD.WUSTL.EDU>
>> Text retrieval packages tend to have a history facility in-built,
>> but there is no way to access it under Z39.50 v2 (unless there is a devious
>> bend of the standard that I am not aware of).
>Actually, there is a save-search and re-execute-search facility in
>Z39.50-1995, which incorporates both v2 and v3 of the standard. V2
>implementors have a mechanism for implementing Extended Services without
>losing compatibility with other V2 implementations. Of course, just
>because the z39.50 standard permits it and specifies it, does not require
>all (or any) of the vendors to actually implement it.
I would like to clarify the comments made following my original posting:
Z39.50-1995 is commonly referred to as 'version 3' and was ratified towards the end of 1995. Most implementors haven't had the time to catch up with the new facilities of version 3 yet, though some did 'jump the gun' and included some anticipated v3 functionality. To quote from the v3 standard:
"'Extended services' is a new facility in Z39.50-1995...Specific extended services include: save a result set, set a periodic query schedule, export a document, order a document and update a database."
I am happy to reiterate my original statement concerning Z39.50 VERSION 2 - using a version 2 Z39.50 engine there is NO concept of search history recall - check the standard if you are in doubt. Any such facilities in a Z39.50 v2 implementation (sort is fairly common) is similar to 'Netscape Enhancements' in the HTML world. Origins implemented with 'enhanced standards'facilities can't work all the time, only with similarly enhanced targets so there must be loss of compatibility.
Alan Jackson