We examine the use of read-time feature conditionals, with particular emphasis on writing portable Common Lisp code which aspires to both forwardsand backwards-compatibility. We examine cases from real libraries which demonstrate the various pitfalls, and propose a scheme for robust treatment of implementation-specific functionality by performing programmatic tests at the appropriate time. We d...

Singleton Arc-Consistency (SAC) [7] is a simple and strong level of consistency but is costly to enforce. To date, research has focused on improving the performance of algorithms that achieve SAC, and comparing algorithms as a preprocessing step before actually solving a problem. Here, we show for the first time how a basic SAC algorithm can be readily incorporated into an open source constrain...

When are economic interactions mediated by prices and transfers, and when are they mediated by variations in the continuation payoffs within a relationship? To address this question, we examine a relationship between two players who periodically face opportunities to undertake randomly generated “projects” that impose a cost on one player and a benefit on the other, as well as opportunities to ...

In this paper, we explain how inheritance and dynamic binding make object-oriented programs diicult to maintain, and we give a concrete example of the problems that arise. We show that the diiculty lies in the fact that conventional tools are poorly suited for work with object-oriented languages, and we argue that semantics-based tools are essential for eeective maintenance of object-oriented p...

Recent work on bringing classical CSP techniques to distributed environments has focused either on backtrack search or on local consistency. We consider the “natural” issue of combining the two techniques. A new distributed algorithm, called MHDC (Maintaining Hierarchical Distributed Consistency), is presented which incorporates distributed consistency into asynchronous backtracking. One of its...

Building a software system from COTS products does not change the importance nor the expense associated with maintenance, evolution and management. COTS-based systems must continue to satisfy evolving user requirements, failures of the system must be dealt with, the system must adapt to the ever-changing environment, and managers must be able to monitor and control the deployed system. These ac...

We present methods for annotating data with the time when it was learned and for answering queries according to what was known at any point in time. Specifically, we present an RDF knowledge representation that associates facts with their transaction times, and a query mechanism that transforms a time-agnostic SPARQL query and a point in time into a new, time-sensitive query. The transformed qu...

Maintaining a secure network connected to the Internet is becoming more difficult as time goes on. New viruses are released daily, higher machine speeds and more sophisticated and automated tools mean that hackers can scan and attack wide sections of the Internet at a time. More consumer broadband connections mean that there is an increasing source of relatively vulnerable high performance comp...