A revision-based logical framework for evolvable software

We describe a natural revision-based logical modelling for evolvable component systems. In this paper, an evolvable component comprises two parts: a supervising process and its supervisee sub-component. The supervisor’s role is to monitor and possibly evolve its supervisee, where evolu-tionary change may be determined purely internally from observations made by the supervisor of the supervisee’s behaviour, or may be a response to external stimuli. We model these systems in a revision-based first-order logi-cal framework in which the logic of the supervisor is a meta-logic to that of its supervisee. This enables evolu-tionary change of the supervisee to be induced by a super-visor’s state revision at the meta-level. To describe the full hierarchical component-based structure requires consider-able mathematical detail, so we introduce the basic ideas in a simple (single component) setting using the familiar Blocks World. We then indicate how this account extends to full structural hierarchies of evolvable components with supervisor processes at any level of the hierarchy. We also explain the difficulties that we encountered in devising a mathematical account of evolvable systems