Whence XQL?

[Jonathan Robie]

At 02:19 PM 3/25/99 -0500, Gavin Thomas Nicol wrote:
 
>I wouldn't bet my farm on that proposal. Folk at QL'98, both database
>and IR, had serious issues with it.

Frankly, I don't know of anything that has been proposed to the XML or web
communities that hasn't found its critics. XQL has found both avid fans and
strong critics. Since you make no specific technical claims here, it is
hard to dismiss what you say with information, but perhaps I can make some
broad statements that address what you are implying here.

Both database and IR people made contact with me at QL'98, showing interest
and appreciation, and we have been in active and enthusiastic
correspondence ever since.

XQL has been more widely implemented than any other XML query language (I
just posted information on six implementations today), and it is closely
related to XSL Patterns.

The main criticism from database folks was that they wanted to see joins
and transformations in XQL. Peter Fankhauser has proposed extensions to XQL
for joins. Declarative transformations are, of course, very useful, but XSL
can also be used for transformations. One of the big reasons for leaving
joins and transformations out of the first version was to make
implementation simple - which is why there are quite a few implementations
of XQL. I suspect that there will be later versions of XQL that include at
least joins; I'm less certain about declarative transformations, since XSL
already exists and can do transformations, but I do really like declarative
transformations.

At least one IR person criticized XQL for doing too much, eg for having the
parent/child relationship in addition to the ancestor/descendant
relationship. This does, in fact, increase the complexity of
implementation, but offers a distinction that I find important.

The number of implementations of XQL shows that there's a fair amount of
interest in it. People who have demonstrated it at trade shows send me
email telling me how impressed people are - for instance, I have been
getting email from Software AG, which is showing XQL at CeBIT this week and
getting very enthusiastic responses. When I discuss XQL at trade shows, I
get enthusiastic responses. So the fact that there are also critics doesn't
bother me.

If you want to implement a query language today, for reasonable effort, and
you want to use a language that has been implemented in other software
systems, I think XQL is a very good choice. There will be a W3C XML Query
Language Activity, and it will develop its own query language, and nobody
can say how similar or different it will be to any existing query language
for XML. I'm sure there will be a lot of interesting and creative work done
by the bright people who will be involved in that group - if you can afford
to wait a year to implement a query language, then by all means wait for
that language to be developed.

Jonathan
 
jonathan at texcel.no
Texcel Research
http://www.texcel.no

xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev at ic.ac.uk
Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1
To (un)subscribe, mailto:majordomo at ic.ac.uk the following message;
(un)subscribe xml-dev
To subscribe to the digests, mailto:majordomo at ic.ac.uk the following message;
subscribe xml-dev-digest
List coordinator, Henry Rzepa (mailto:rzepa at ic.ac.uk)