xml-dev - RE: power uses of XML vs. simple uses of XML

[Kay Michael <Michael.Kay@icl.com>]

> On the other hand, if you do application-level validation, 
> the logic must be duplicated across n programs. This presents a versioning

> problem. When there is a rule change, you must do n updates to source
code, 
> instead of updating a single schema.

Doing the validation in a SAX Filter application that can be inserted in
front of any "real" application (and removed when the sender is sufficiently
trusted) is an alternative that works very nicely.

One advantage of dong the validation this way is that you are likely to have
rather more flexibility in deciding what to do when the data is invalid. For
example, if you want to process the parts of the message that were OK,
reject the others, and update a database to say which parts you dealt with
and which you didn't, then doing this in your own code may well prove easier
than trying to intercept the error messages from a validating parser.

(I know I'm being a bit heretical here and I wouldn't claim that this is the
right advice for EVERY project!)

Mike Kay

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