TAS and IsaWin: Generic Interfaces for Transformational Program Development and Theorem Proving
We present a new approach to the implementation of graphical user interfaces (GUIs) for formal program development systems like transformation systems or interactive theorem provers. Its distinguishing feature is a generic, open system design which allows the development of a family of tools for different formal methods on a sound logical basis with a uniform appearance. The context of this work is the UniForM project [KPO+95], the aim of which is to develop a framework integrating different formal methods in a logically consistent way. Consistency is achieved by encoding formal methods such as CSP and Z in the theorem prover Isabelle [Pau94], which is used to perform the program development as well as to prove the correctness of the transformation rules. One of the main UniForM objectives is to enable non-expert users to actually perform at least part of the developmen~ themselves. Hence there is a crucial need for an encapsulation technique of these Isabelle encodings providing a generic way of building graphical user interfaces.

title: Collage Grammars for Collision-Free Growing of Objects in 3D Scenes
abstract: In the real world, solid objects rarely collide without serious damage. We study collision-freeness in the context of collage grammars, which are picture- and scene-generating devices based on hyperedge replacement. We identify a type of collage grammars that generate only collision-free collages, and prove the undecidability of the problem whether an arbitrary collage grammar generates any collision-free collage. Moreover, we discuss collision avoidance in the derivation process as an appropriate tool for practical modelling purposes.

title: Tactic-Based Optimized Compilation of Functional Programs
abstract: Within a framework of correct code-generation from HOL-specifications, we present a particular instance concerned with the optimized compilation of a lazy language (called MiniHaskell) to a strict language (called MiniML). 
 
Both languages are defined as shallow embeddings into denotational semantics based on Scott's cpo's, leading to a derivation of the corresponding operational semantics in order to cross-check the basic definitions. 
 
On this basis, translation rules from one language to the other were formally derived in Isabelle/HOL. Particular emphasis is put on the optimized compilation of function applications leading to the side-calculi inferring e.g. strictness of functions. 
 
The derived rules were grouped and set-up as an instance of our generic, tactic-based translator for specifications to code.

title: Modelling Object Typicality in Description Logics
abstract: We present a semantic model of typicality of concept members in description logics (DLs) that accords well with a binary, globalist cognitive model of class membership and typicality. We define a general preferential semantic framework for reasoning with object typicality in DLs. We propose the use of feature vectors to rank concept members according to their defining and characteristic features, which provides a modelling mechanism to specify typicality in composite concepts.

title: Equilibria in social belief removal
abstract: In studies of multi-agent interaction, especially in game theory, the notion of equilibrium often plays a prominent role. A typical scenario for the belief merging problem is one in which several agents pool their beliefs together to form a consistent “group” picture of the world. The aim of this paper is to define and study new notions of equilibria in belief merging. To do so, we assume the agents arrive at consistency via the use of a social belief removal function, in which each agent, using his own individual removal function, removes some belief from his stock of beliefs. We examine several notions of equilibria in this setting, assuming a general framework for individual belief removal due to Booth et al. We look at their inter-relations as well as prove their existence or otherwise. We also show how our equilibria can be seen as a generalisation of the idea of taking maximal consistent subsets of agents.

title: Logical Foundations of Negotiation: Outcome, Concession, and Adaptation
abstract: This paper provides a logical framework for negotiation between agents that are assumed to be rational, cooperative and truthful. We present a characterisation of the permissible outcomes of a process of negotiation in terms of a set of rationality postulates, as well as a method for constructing exactly the rational outcomes. The framework is extended by describing two modes of negotiation from which an outcome can be reached. In the concessionary mode, agents are required to weaken their demands in order to accommodate the demands of others. In the adaptationist mode, agents are required to adapt to the demands of others in some appropriate fashion. Both concession and adaptation are characterised in terms of rationality postulates. We also provide methods for constructing exactly the rational concessions, as well as the rational adaptations. The central result of the paper is the observation that the outcomes obtained from the concessionary and adaptationist modes both correspond to the rational outcomes. We conclude by pointing out the links between negotiation and AGM belief change, and providing a glimpse of how this may be used to define a notion of preference-based negotiation.

title: Modeling and Solving Semiring Constraint Satisfaction Problems by Transformation to Weighted Semiring Max-SAT
abstract: We present a variant of theWeighted Maximum Satisfiability Problem (), which is a modeling of the Semiring Constraint Satisfaction framework. We show how to encode a Semiring Constraint Satisfaction Problem (SCSP) into an instance of a propositional Weighted Max-SAT, and call the encoding Weighted Semiring Max-SAT (WS-Max-SAT). The clauses in our encoding are highly structured and we exploit this feature to develop two algorithms for solving WS-Max-SAT: an incomplete algorithm based on the well-known GSAT algorithm for Max-SAT, and a branch-and-bound algorithm which is complete. Our preliminary experiments show that the translation of SCSP into WS-Max-SAT is feasible, and that our branch-and-bound algorithm performs surprisingly well. We aim in future to combine the natural flexible representation of the SCSP framework with the inherent efficiencies of SAT solvers by adjusting existing SAT solvers to solve WS-Max-SAT.

title: A Relaxation of a Semiring Constraint Satisfaction Problem Using Combined Semirings
abstract: The Semiring Constraint Satisfaction Problem (SCSP) framework is a popular approach for the representation of partial constraint satisfaction problems. In this framework preferences (semiring values) can be associated with tuples of values of the variable domains. Bistarelli et al.  define an abstract solution to a SCSP which consists of the best set of solution tuples for the variables in the problem. Sometimes this abstract solution may not be good enough, and in this case we want to change the constraints so that we solve a problem that is slightly different from the original problem but has an acceptable solution. In  we propose a relaxation of a SCSP where we define a measure of distance (a semiring value from a second semiring) between the original SCSP and a relaxed SCSP. In this paper we show how the two semirings can be combined into a single semiring. This combined semiring structure will allow us to use existing tools for SCSPs to solve Combined Semiring Relaxations of SCSPs. At this stage our work is preliminary and needs further investigation to develop into a useful algorithm.