XPi: A Typed Process Calculus for XML Messaging

We present XPi, a core calculus for XML messaging. XPi features asynchronous communications, pattern matching, name and code mobility, integration of static and dynamic typing. Flexibility and expressiveness of this calculus is illustrated by a few examples, some concerning description and discovery of web services. In XPi, a type system disciplines XML message handling at the level of channels, patterns and processes. A run-time safety theorem ensures that in well-typed systems no service will ever receive documents it cannot understand, and that the offered services, even if re-defined, will comply with the declared channel capacities.