Towards a refinement calculus for concurrent real-time programs

We define a language and a predicative semantics to model concurrent real-time programs. We consider different communication paradigms between the concurrent components of a program: communication via shared variables and asynchronous message passing (for different models of channels). The semantics is the basis for a refinement calculus to derive machine-independent concurrent real-time programs from specifications. We give some examples of refinement laws that deal with concurrency.

Dartboard arrangements with a concave penalty function

This paper investigates combinatorial arrangements of the dartboard to maximize a penalty function derived from the differences of adjacent sectors. The particular penalty function is constructed by summing the absolute differences of neighbouring sectors raised to a power between zero and one. The arrangement to give the maximum penalty is found

OntoRama: Browsing RDF ontologies using a hyperbolic-style browser

This paper presents a Java-based hyperbolic-style browser designed to render RDF files as structured ontological maps. The program was motivated by the need to browse the content of a web-accessible ontology server: WEB KB-2. The ontology server contains descriptions of over 74,500 object types derived from the WordNet 1.7 lexical database and can be accessed using RDF syntax. Such a structure creates complications for hyperbolic-style displays. In WEB KB-2 there are 140 stable ontology link types and a hyperbolic display needs to filter and iconify the view so different link relations can be distinguished in multi-link views. Our browsing tool, OntoRama, is therefore motivated by two possibly interfering aims: the first to display up to 10 times the number of nodes in a hyperbolic-style view than using a conventional graphics display; secondly, to render the ontology with multiple links comprehensible in that view.

Verification and validation of autonomous systems

NASA is working on complex future missions that require cooperation between multiple satellites or rovers. To implement these systems, developers are proposing and using intelligent and autonomous systems. These autonomous missions are new to NASA, and the software development community is just learning to develop such systems. With these new systems, new verification and validation techniques must be used. Current techniques have been developed based on large monolithic systems. These techniques have worked well and reliably, but do not translate to the new autonomous systems that are highly parallel and nondeterministic.

On the relative complexity of labelled modal tableaux

We investigate the relative complexity of two free-variable labelled modal tableaux(KEM and Single Step Tableaux, SST). We discuss the reasons why p-simulation is not a proper measure of the relative complexity of tableaux-like proof systems, and we propose an improved comparison scale (p-search-simulation). Finally we show that KEM p-search-simulates SST while SST cannot p-search-simulate KEM.