Re: Beyond schema

[Christian Nentwich <c.nentwich@cs.ucl.ac.uk>]

> When we receive the data (the xml message) we need to check the structure
> (is the message valid according to the schema) but we also need to
> implement  particular business rules. For exemple, a field A in the message
> is required if, and only if, the value of some other field B in the message
> is defined in a extrnal list of values. The DTD (and schema) can only
> prescribe that the field A is optional since we cannot know in advance what
> will be the content of the other fields (B in this example).
> Is there some rules, standard architectures or good practices to use ? It

Sounds like a prime case for using xlinkit (http://www.xlinkit.com)! 
particularly if you need to check constraints between different documents.. 
like your externally defined values. Also, have a look at Schematron (google) 
for single document validation.

Christian