<XML><RECORDS><RECORD><REFERENCE_TYPE>10</REFERENCE_TYPE><REFNUM>6962</REFNUM><AUTHORS><AUTHOR>Gay,S.J.</AUTHOR><AUTHOR>Hole,M.J.</AUTHOR></AUTHORS><YEAR>2003</YEAR><TITLE>Types and Subtypes for Correct Communication in Client-Server Systems</TITLE><PLACE_PUBLISHED>DCS Tech Report</PLACE_PUBLISHED><PUBLISHER>Dept of Computing Science, University of Glasgow</PUBLISHER><ISBN>TR-2003-133</ISBN><LABEL>Gay:2003:6962</LABEL><ABSTRACT>We review an extension of the pi-calculus with a static type system which supports high-level specifications of extended patterns of communication, such as client-server protocols. We then present a subtype relation that allows protocol specifications to be extended in order to describe richer behaviour; an implemented server can then be replaced by a refined implementation, without invalidating type-correctness of the overall system. We show how this subtyping relation can be integrated into the type system, and use the POP3 protocol as a concrete example of this technique. This report is a revised and extended version of our paper "Types and Subtypes for Client-Server Interaction", presented at the ESOP'99 conference.</ABSTRACT></RECORD></RECORDS></XML>