Re: Practical XSL

Subject: Re: Practical XSL
From: Keith Visco <kvisco@xxxxxxxxx>
Date: Thu, 18 Feb 1999 14:13:27 -0500
I agree with Mark on this issue. We are heavily using XSL on many
projects. We have successfully deployed to our Intranet applications
using XML and XSL technologies. We have about 5000 employees accessing
our Intranet. One of our applications is an interface to our corporate
LDAP directory server. It gets on average 20-30 requests (directory
lookups) per minute. I our system can handle a load of approx 160
requests per minute depending on the queries being run against the
directory server and the amount of data being returned.

We convert the data from the directory server to XML on the fly and then
use XSL stylesheets to translate the XML data to well formed HTML. We
also can return just the XML so that other applications can get the XML
stream and format it anyway they see fit. 

We can then change the look and feel by simply changing the XSL
We have some applications written using the proposal version of XSL. We
have some written in using the latest spec. There is nothing that states
we need to update these applications when XSL changes. Of course it is
our goal to stay current. But we have something working...and it's easy
to maintain.

As XSL changes we will update the Stylesheets when we are ready to do
so. And as mark mentioned you can devise a stylesheet to "transform" the
existing one into the new one. Since of course XSL is an XML application
so the existing stylesheets are XML documents. The only issue is
transforming extensibility mechanisms like script. So some things are
left to do by hand. That is a tradeoff for using a new up and coming

Performance is an issue. We have 3 different XSL processors that we are for each version of the spec. The processor we have for the
proposal version is fairly quick. In implementing my current XSL
processor (XSL:P) I first focused on functionality. I am now starting to
look at performance and will continue to optimize it for both speed and
memory utilization. 

Since our applications are already in place it only takes a second to
pop in a new version of an XSL processor, so as performance of XSL
processors and XML parsers increase then so can the performance of the
applications that depend on them.

There are things you can do to speed up the stylesheets. For example
using <xsl:for-each select="foo"> is faster in XSL:P than using
<xsl:apply-templates selece="foo"> because in a for-each you are
essentially giving the processor the template to use, while in an
apply-templates you are asking the processor to find the appropriate
template to use.

It truly depends on each specific case to decide whether the tradeoffs
of using the current XSL WD and associated implementations are the right
choice for the given task at hand. 


Mark Birbeck wrote:
> Paul Prescod wrote:
> > "Livingstone, Stephen" wrote:
> > > Is anyone doing anything serious with XSL yet? If not (for those who
> > > decide these things) when is it likely that we shall be
> > able to reliably
> > > use XSL?
> >
> > It will be safest to use XSL seriously when it becomes a W3C
> > recommendation.
> Don't agree!
> I replied privately to Stephen with mention of a site that we are about
> to launch which is an online magazine. Within it there are hundreds of
> articles and a database full of information on companies, countries,
> people, events and so on. All are cross-referenced with XLink-type
> relationships, and then XSL is used to produce HTML for the layout and
> in particular the 'real' links needed.
> Now, if XSL changes next week, we have about eight (that's eight)
> stylesheets to change. Might take a few hours, and then it's off down to
> the pub. Even if certain concepts change I can't see us being
> inconvenienced more than a few days. When the IE4 to IE5 changes
> happened it took us an afternoon.
> And if you have a hundred stylesheets - and I would be surprised if
> anyone has yet, given the early stages we are at - then you can devise a
> stylesheet to transform them anyway.
> BUT ...
> Imagine NOT using XSL. We would have implemented a boring old,
> traditional solution to the web site. We would not have been able to
> deliver the richness of cross-referencing that we have, and if we did it
> would be pretty much impossible to maintain. And THEN when XSL had
> settled we'd have to start the conversion process, and therefore be a
> generation of technology behind.
> I say give it a go! You have nothing to lose, and I can assure you that
> most problems to do with performance can be 'worked round' for now,
> until the next generation comes along. It's really not as difficult as
> people are making out.
> Regards,
> Mark
> Mark Birbeck
> Managing Director
> Intra Extra Digital Ltd.
> 39 Whitfield Street
> London
> W1P 5RE
> w:
> t: 0171 681 4135
> e: Mark.Birbeck@xxxxxxxxxxxxx
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