Re: The imprecision of Z39.50

> Date: Thu, 3 Jul 2003 13:30:40 +1000
> From: Alan Kent <ajk@mds.rmit.edu.au>
> 
> I am home sick today, so sending this may be dangerous (inaccurate),
> but it makes sense to me at the moment! *-)

Wow.  You sure know how to party on your sick-day!  :-)

This is a fascinating piece, the most interesting thing I've read in a
long while; and I am not at all going to be able to reply to all of
it.  But it's worth a comment or two.

> For example, if I load the same data into two systems claiming to be
> SQL conformant, then I know the same SQL query on both systems will
> return the same results.

Please excuse me while I laugh so hard that major internal organs come
spurting out my nose.  As someone who's spent much too much of the
last few years porting web-based applications between MS-SQL, Sybase,
PostgreSQL and MySQL, I am here to tell you that there are _vast_
differences between SQL implementations.

> But there seems to me to be one central place in Z39.50 where things
> are messy, and that is where terms and attributes meet.

Yes, absolutely.  It was recognition of this very fact that led to the
design of the Attribute Architecture.  Whether the AA successfully
addresses that defect is another question -- and one that, I fear, may
never be answered, since it seems that its technical merits or lack or
them have been completely overwhelmed by its political failings.
Basically, it's not been sufficiently widely implemented to judge how
well it works, except in closed-domain special cases such as the Zthes
profile and searching ZeeRex databases.

> [Much interesting stuff snipped.]

> I think the new attribute architecture has a flaw. I was not really
> involved in its development, but my seconding guessing is that the
> model used was to try and make it abstract by avoiding dependence on
> how it might be implemented. That is, lets define lots of query
> operators that people have needed to do in the past but leave it up
> to developers how to implement it. On the surface this sounds good.

Yes, that was pretty much the intention as I remember it.

> Rather than only be critical (I am certainly not trying to offend
> those have put lots of time and effort into it), I guess I should
> present something constructive. If I was to design the ideal
> solution for myself, ignoring all other people's requirements, I
> would start from a definition of the basics of how I (and I think
> most vendors) implement Z39.50.

In fact, we very deliberately did _not_ consider how various
attributes might be implemented.  The prevailing feeling was that the
AA should be, if you like, declarative rather than procedural -- it
should say _what_ is to be done without consideration of _how_.  So
that's why it doesn't fit the approach you're trying to take here.
(Whether that was the right approach or not, I will not try to argue
:-)

 _/|_	 _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "Innocent, unbiased observation is a myth" -- P.B. Medawar,
	 1969, _Induction and Intuition in Scientific Thought_

--
Listen to my wife's new CD of kids' music, _Child's Play_, at
	http://www.pipedreaming.org.uk/childsplay/

Received on Thursday, 3 July 2003 04:25:48 UTC