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Re: The imprecision of Z39.50

From: Mike Taylor <mike@indexdata.com>
Date: Fri, 04 Jul 2003 11:11:21 +0100
To: ajk@mds.rmit.edu.au
CC: www-zig@w3.org
Message-Id: <E19YNXF-00025h-00@auntie.miketaylor.org.uk>

> Date: Fri, 4 Jul 2003 08:58:42 +1000
> From: Alan Kent <ajk@mds.rmit.edu.au>
> 
> Defining a model does not make it procedural.  A complaint I have
> with the AA *specification* as it is written is that there is an
> *implicit* model, but I suspect the model assumed by descriptions of
> different attributes is different.

This may be so.

> If the model was explicit I think these issues would have been
> spotted. I think the correct way to express your line of argument is
> to say it was intended to keep things open to allow people to
> implement it in different ways.
> [...]
> More centrally, I have two questions/observations.
> [...]
> (1) Should the attribute archtecture try to fit it with the overall
>     protocol (including things like scan - sort also can use
>     attributes)
> [...]
> (2) Ignoring the model I put up, I cannot work out how the AA
>     supports querying on title as a complete value and title as
>     words in a reliable way.

All I can say to all this is: I wish you'd been around when we were
defining this stuff.  Looks like your clear thinking would have been
very beneficial to the whole project.  I fear it may be too late now,
though.  (Anyone else going to chip in?)

>     It seems like you have to look for about 10 magic combinations
>     of attributes to work out which form to use. And I cannot work
>     out these combinations from reading the spec.

A brief scan of the Utility Set doucment at
	http://lcweb.loc.gov/z3950/agency/attrarch/util.html 
suggests to me that whole-field matching is the default, and you can
get word-matching by combining the Expansion/Interpretation attributes
for Right Truncation On Word Boundary and Left Truncation On Word
Boundary (so @attr util 5=3 @attr util 5=4 "word").  I'd be the first
to admit, though, that this is hardly the most elegant way to express
what you want to say here.

Another candidate would be the Format/structure attribute
AllTheseWords (or, equivalently in the case of a single word),
AnyOfTheseWords.  (@attr util 9=2 "term")

I'm amazed no-one else has brought this up before.

>     This is not a question of implementation, this is purely a
>     question of interpretation of a query.  The individual
>     attributes are one thing, but the combination of them that gets
>     into deep water pretty quickly.

... which is ironic, since it was _precisely_ that fault in BIB-1 that
we were trying to address.

> I certainly appreciate what you mean when you talk about the
> differences between SQL engines. I think more that it is *possible*
> to write queries where they will do the same thing on all
> installations.

Well, sure.  It's possible to write Z39.50 queries that will do the
same thing on all installations, too.  The question is whether you can
express the particular query you want in such a way -- and the answer
for both systems seems to be no.

 _/|_	 _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "Anyone can see that Michael Owen represents Carlsberg
	 and Reebok.  But you'd need binoculars to notice that he
	 also plays for Liverpool" -- George Monbiot, writing in
	 the _Guardian_

--
Listen to my wife's new CD of kids' music, _Child's Play_, at
	http://www.pipedreaming.org.uk/childsplay/
Received on Friday, 4 July 2003 06:11:47 GMT

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