This paper extends earlier work by its authors on formal aspects of the processes of contracting a theory to eliminate a proposition and revising a theory to introduce a proposition. In the course of the earlier work, Gardenfors developed general postulates of a more or less equational nature for such processes, whilst Alchourron and Makinson studied the particular case of contraction functions that are maximal, in the sense of yielding a maximal subset of the theory (or alternatively, of one of (...) its axiomatic bases), that fails to imply the proposition being eliminated. In the present paper, the authors study a broader class, including contraction functions that may be less than maximal. Specifically, they investigate "partial meet contraction functions", which are defined to yield the intersection of some nonempty family of maximal subsets of the theory that fail to imply the proposition being eliminated. Basic properties of these functions are established: it is shown in particular that they satisfy the Gardenfors postulates, and moreover that they are sufficiently general to provide a representation theorem for those postulates. Some special classes of partial meet contraction functions, notably those that are "relational" and "transitively relational", are studied in detail, and their connections with certain "supplementary postulates" of Gardenfors investigated, with a further representation theorem established. (shrink)

High-level robot controllers often need to specify event-driven behavior and they operate low-level processes which change the world in a continuous fashion. While non logic-based control languages have existed for some time to address these issues, this is not the case for logic-based languages. To remedy the situation, we show how to incorporate continuous change and event-driven behavior into the action language GOLOG. Besides proposing a suitable semantics for the new language, which we call cc-Golog, we show how a robot (...) architecture where a high-level controller communicates via messages with low-level routines can be modeled naturally in this new dialect. Finally, we demonstrate how on-line execution and off-line projection can be combined in this language. (shrink)