RE: Impact of XML on Data Modeling

> In fact, if you are just talking messages, there may be no 
> defined 'application' data model at all (at least not an XML 
> based one).  Protocols such as VoIP and HTTP are generally 
> defined mainly in terms of the messages that flow between nodes.

Sure (though VoIP and HTTP are lower down the stack: they are channels of
communication rather than application message formats. Neither of them knows
anything about business objects). 

I've certainly come across situations where people were struggling to define
messages between two applications because they hadn't defined the common
data model first. One application was using the term "retailer" to refer to
a shop, the other was using it to refer to a chain of shops under common
ownership, and untold confusion arose as a result. 

The other side of the coin is that I've seen people try to define the
application data model as an XML Schema, and then wonder why their messages
were so large - they were sending masses of data that the recipient didn't
need, simply because the schema said it was mandatory. They hadn't separated
data modelling from message design. 

Michael Kay
http://www.saxonica.com/