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RE: triggers in XML

Subject: RE: triggers in XML
From: Curtis Fisher <cdfisher@xxxxxxxxxx>
Date: Sun, 20 Oct 2002 15:57:55 -0500
curtis fisher
Okay, since some people consider this an irrelevant question for this
forum, I will answer with what I know.  Maybe the reason folks aren't
answering is because the questions are not as clear as they could be.  

First Question: Triggers in a database are used to perform some action
upon an insert, update or delete on a column in a row of the database.
Typically, they cannot be rolled back (or undone) once the trigger has
been performed unless you program a ton of stuff to check integrity
first, before executing the trigger.  It gets hairy in a hurry!
Triggers can be very helpful to the application programmer, but are
frowned upon by DBA's because some actions can be performed outside of
the scope of the original transaction.

Second Question: Yes there is a way to approximate "Trigger Like"
behavior when updating XML files (at least this is what I believe you
are asking).  You could use an Event Parser like SAX which performs a
"callback" to a function when it locates the Node of interest (whose
name was previously registered after the parser was instantiated).  Your
function would likely perform some type of modification or calculation
on the Node, at which time you could call another function that could
update another node with another parser and so on and so forth...  You
would then have emulated the approximate behavior and problems
associated with database triggers found in a DBMS, in XML.

Why would you want to do this?  If I have misunderstood your intent,
please forgive me.  Using a SAX parser is only one way to go about this,
and the parser would have to be part of the architecture and usable with
whatever language (PHP, Java, ECMA262) was selected.

Our architectures for our products use a database for content storage
and management, then publish XML to files which the web server and
associated PHP engine transform to HTML using the Sablotron XSLT
processor.  That way we get all the database goodies and the benefits of
XSLT output.

If you need any other information feel free to contact me at
cdfisher@xxxxxxxxxx

Cheers,

Curtis Fisher
President 
Professional Content LLC  
5421 Sterling Ave
Kansas City, MO 64133
Bus:  816.353.4501
Cell: 816.914.8793
http://www.procontent.net 

-----Original Message-----
From: owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx
[mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx] On Behalf Of karan bhasin
Sent: Sunday, October 20, 2002 2:20 PM
To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
Subject:  triggers in XML

 I am working on a project to ensure the database integrity constraints
on XML files. I would like to know the answer to following questions
1) why triggers are an issue in the traditional database systems and
considered to circumvent the database integrity.
2) is there a poosible way to implement triggers for XML files
If anyone has any answers or suggestions for this, please do reply back.
Thanks
Jaskaran



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