  This document discusses the definition of the Parameter Description Language
(PDL). In this language parameters are described in a rigorous data model. With
no loss of generality, we will represent this data model using XML. It intends
to be a expressive language for self-descriptive web services exposing the
semantic nature of input and output parameters, as well as all necessary
complex constraints. PDL is a step forward towards true web services
interoperability.
