Meaningful error messages from a web service

[Joshua Ellul]

Hi,

I am creating a web service that returns a double value.... if however, one
of the user passed parameters are incorrect I would like to return to the
user a meaningful message (rather than a -1 for example)... I believe this
can be done by using SOAP messages....

Could anyone guide me to a simple example of using such a message within the
web service?

Thanks,

Josh