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Re: [xml-dev] reasons why an XML instance must be validated with a XML schema

Writing a schema is also helpful for developer to developer communication. 
It captures the XML specification in a reasonably compact, (mostly) 
unambiguous specification.  That helps in the initial development, and also 
perhaps later when the system is extended in some unforeseen way, perhaps to 
another platform.

As Robert mentions, during development using a validating XML parser 
verifies the implementation, and to some degree a working implementation can 
be used to validate the schema is correct.

BTW - another issue to consider is that most systems evolve over time.  If 
the systems evolve in lock-step then running without validation in 
production may be an option (and just run validation in development).  But 
if they are likely to evolve on a separate time line (perhaps due to 
functionality not specifically related to the XML processing), it may be 
worth including validation in the production version, because even changes 
in areas that seem well away from the actual XML bit may have repercussions 
in the way the XML operates.  After all, real systems often through up 
scenarios that the test cases miss, and the quicker you can detect them, fix 
them and update the test suite the better.


Pete Cordell
Codalogic Ltd
Interface XML to C++ the easy way using XML C++
data binding to convert XSD schemas to C++ classes.
Visit http://www.codalogic.com/lmx/ for more info

----- Original Message ----- 
From: "Robert Koberg" <rob@koberg.com>
To: <ilangocal@yahoo.com>
Cc: <xml-dev@lists.xml.org>
Sent: Tuesday, September 09, 2008 6:31 PM
Subject: Re: [xml-dev] reasons why an XML instance must be validated with a 
XML schema

> On Sep 9, 2008, at 11:05 AM, ilango wrote:
>> I just started working on a project that uses JMS/WebSphere MQ with
>> non-J2EE systems to build an enterprise system. We would be using
>> XML for all the request/response message flows that take place
>> between two system (for example, a JMS Listener and one or more than
>> one queues.
>> I was posed with the following scenario: Our Listener Module submits
>> document requests in XML formatted data into an input message queue
>> monitored by a document generaton engine.
>> The need for validating the XML naturally arises.  Should the XML be
>> validated against an XML schema.
>> The question they raised was:
>> If so, why should we use XML schema to validate XML?
> It might be wise in the beginning (development/testing) to ensure your
> system is working as advertised, but I don't see why you would need to
> do it for every instance at runtime. The two systems you mention don't
> sound like you would be taking things from the wild, rather building
> the structures up in your own code that you control. So, probably
> parsing the document to find if there are inappropriate nulls or java
> types would be plenty.
> best,
> -Rob
>> So this is the question I am trying to answer for myself and for my
>> team here.
>> Any suggestions, ideas are gratefully accepted.
>> thanks
>> ilango

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