RE: [xsl] A theoretical question

Subject: RE: [xsl] A theoretical question
From: "Ray Lukas" <rlukas@xxxxxxxxxxx>
Date: Thu, 1 Mar 2001 10:33:12 -0500
No problem my friend:
I am also just learning this stuff. I don't know what your ultimate goal is
in the XML universe of technology. I myself an big into Java and so I found
a pretty good book on Java and XML and of course all of the related
technologies. They are quite a few out there now. This book is the Java ad
XML book from O'Reilly (ISBN# 0-596-00016-2). It is a pretty good book.. But
enough of that.

XSL is the Extensible Stylesheet Language. And it is for transforming and
translating XML data from one format to another. Okay so what is this other
format. It can be almost anything, text output, and even binary output. Well
if the output format is some kind of binary format like a PDF (Acrobat
Reader) file you would use a Formatting Object in your XSL file. This
formatting object does the binary crunching that can produce a PDF file. You
can get the specialized formatting object from a lot of places. So that is
what a formatting object is for. It takes XML data and converts it into some
kind of binary output.

So what the heck is XSLT for. Well HTML and XML are not binary they are
normal text output. So XSLT can take a XML file and parse it and reformat is
into another text based output file, like XML and HTML or any other format
you want. I find it helpful to think about XSLT as fancy parser and
translator. Getting really good at this stuff is some work. I am on that
quest right now. I have several tools which I want to integrate together.
XML provides a mean of obtaining data independence. Much like the Java
language provides language independence. So each of my tools will accept XML
as input and generate XML as output. Output from one tools will then be used
by another tool after of course it is formatted (translated) into the
correct format for that receiving tool. So XSLT can be used to re-structure
one XML file into another XML file. Sometimes my XML might need to go to a
user. So XSLT can be used to, instead of generating another XML file to
another tool, generate a HTML file for a browser.  See what I am saying

Now a fancy parse like this XSL needs a way to "query and reference" the
tags inside of your XML and so there is something called XPath. Now XPath is
a specification of its own and defines how a specific items within an XML
document can be located (queried). So using this XPath thing you can obtain
a series of nodes from the input XML file. It is kind of like getting a
record set from a relational database. And the result of this query is even
called a "node set". From this node set you generate your output. There is a
lot of interesting things that you can do with XPath stuff. Getting some
skills in this I think would really be key.

The moral is to also try and gain an understanding of XSL, (the general
topic) and XPath (the query engine). These two things together seem to be
the corner stones. The formatting object stuff you most likely will not need
to write since you will almost always use someone else's.  Then the final
thing, which I plan on using most, is the XSLT stuff which allows you to
construct templates. These templates define a set of rules that are applied
to your nodeset (remember the XPath stuff). An XSLT file is really a series
of these templates. These templates are called over and over and over again
by the XSLT processor matching and transforming sections of your XML input
file to produce your (text based) output.

I know that this all seems really confusing. But have faith and just try and
stick with it. I guess that last thing which I want to mention (without
writing a book) is there are several XML frameworks which can help you use
this stuff. I started working with something called Cocoon. Cocoon is
produced by Apache ( I am, as time permits and it usually
doesn't, trying to learn about it. May the Cocoon Gods forgive me but a lot
of people have some misery getting this installed and working. I do not know
if Apache is the best or even how one would really define what best even
means. It all depends. I am just trying to say that it exists and is free
and works and is good if you want to learn more. If you need a hand you may
call on me. I will try and help you, as best I can. I am not an expert but I
am will to try and give you a hand.

I hope that this helps you.
Ray Lukas
(work) 978.262.6297
(fax) 978.262.6777

 -----Original Message-----
From: 	owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx
[mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx]  On Behalf Of mcarrasc
Sent:	Thursday, March 01, 2001 9:05 AM
To:	Lista XSL
Subject:	[xsl] A theoretical question


   I´m beginning with XSL, and i have a big gap in my
small knownledgements :) and I guess you don´t mind to
answer me, thanks.

I´m really confuse with XSL, XSLT, XSL Formatting
Objects.. I don´t know who is who here, because i was
searching in the W3C website, and there are
recommendations for all of them. What is the
difference between XSL and XSL FO? And XSL and XSLT?
and all the possible combinations among them :)

Thank you very much, and congratulations for your
list. It´s very useful. Thanks again.

                                       Marta Carrasco

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