Types, Orthogonality and Genericity: Some Tools for Communicating Process Architectures

samson@comlab.ox.ac.ukAbstract. We shall develop a simple and natural formalization of the idea of client-server architectures, and, based on this, define a notion of orthogonality betweenclients and servers, which embodies strong correctness properties, and exposes therich logical structure inherent in such systems. Then we generalize from pure clientsand servers to components, which provide some services to the environment, and re-quire others from it. We identify the key notion of composition of such components, inwhich some of the services required by one component are supplied by another. Thisallows complex systems to be built from ultimately simple components. We show thatthis has the logical form of the Cut rule, a fundamental principle of logic, and that itcan be enriched with a suitable notion of behavioural types based on orthogonality, insuch a way that correctness properties are preserved by composition. We also developthe basic ideas of how logical constructions can be used to develop structured inter-faces for systems, with operations corresponding to logical rules. Finally, we showhow the setting can be enhanced, and made more robust and expressive, by usingnames (as in the π-calculus) to allow clients to bind dynamically to generic instancesof services.Keywords. client, server, type, orthogonality, genericity, interaction.