In this paper, we propose an intermediate approach to web service
specification. In particular, our approach balances the ease of 
expressivity offered by informal documentation with the mathematical 
rigor provided by traditional formalisms.  We present a technique 
that integrates the use of regular expressions in WSDL specifications 
to constrain the format of input and output values to and from web 
services.  This approach provides the basis for automating the 
generation of both client- and server-side checking wrappers.