Being served: The Purposes, Strengths and Limitations of Formal Service Modelling

Abstract

Although the Object-Oriented community is now largely committed to formal service description, its ramifications have yet to be widely appreciated. A formal service description is a model (constructed by an observer: the analyst) of a service desired by an agent (in the context of the agent’s world model). The assessment of its validity involves subjecting it to such operations as’ horizontal’ composition (with models of other services with which it should interoperate),’ vertical’ composition (with models of platforms on which servers propose to implement it), closure (to determine its possible behaviours), and restriction (to more limited ontologies, e.g. with respect to’ legacy’ systems). These acts of analysis can reveal flaws both in the observer’s understanding and in the agent’s world model. In the latter case, the effects are clinical (as in psychoanalysis), altering the agent’s world model, and the services desired, along a’ trajectory’ in the space of all models. Although most of the mathematical frameworks familiar to Computer Science (e.g. set theory, abstract algebra, modal logic) are suitable vehicles for formal service modeling, none can represent such’ higher order’ trajectories. Formal service modeling therefore presents a serious challenge both to our theory and to our praxis.