Han Reichgelt

The token reification approach to temporal reasoning

Abstract The approach to temporal reasoning which has proven most popular in AI is the reified approach. In this approach, one introduces names for events and states and uses special predicates to assert that an event or state occurs or holds at a particular time. However, recently the reified approach has come under attack, both on technical and on ontological grounds. Thus, it has been claimed that at least some reified temporal logics do not give one more expressive power than provided by alternative approaches. Moreover, it has been argued that the reification of event and state types in reified temporal logics, rather than event and state tokens , makes the ontology more complicated than necessary. In this paper, we present a new reified temporal logic, called TRL , which we believe avoids most of these objections. It is based on the idea of reifying event tokens instead of event types. However, unlike other such attempts, our logic contains “meaningful” names for event tokens, thus allowing us to quantify over all event tokens that meet a certain criterion. The resulting logic is more expressive than alternative approaches. Moreover, it avoids the ontologically objectionable reification of event types, while staying within classical first-order predicate logic.

Software engineering services for export and small developing economies

Abstract A number of authors and multi‐national organizations have suggested that providing information services, and in particular software engineering and programming services, for export afford an important economic opportunity for poor countries. Throughout the world, developing countries have acted on this advice. This paper will argue that the opportunities for software engineering services in particular are limited, at least for small developing economies. The main argument is that software engineering and programming are labor‐intensive activities and that small developing countries simply do not have the required resources to acquire or train a sufficient number of software engineers and programmers. Any development policy that blindly follows the tenet that small developing countries can improve their economic position through the provision of information services for export is therefore bound to fail. Hence, more sophisticated policies are called for. This paper will also examine a number of such policy options, including an innovative human resource development policy being developed in Jamaica. Keywords: Information services for export, economic development policy, small developing countries, Jamaica

ACT-P: a configurable theorem-prover

There has been a considerable amount of research into the provision of explicit representation of control regimes for resolution-based theorem provers. However, most of the existing systems are either not adequate in that they do not allow the user to express any arbitrary control regime, or are too inefficient to be of practical use. In this paper a theorem prover, ACT-P, which is adequate but retains satisfactory efficiency is presented. It does so by providing a number of user-changeable heuristics which are called at specific points during the search for a proof. The set of user-changeable heuristics was determined on the basis of a classification of the heuristics used by existing resolution-based theorem provers.

Resolution theorem proving in reified modal logics

This paper is concerned with the application of the resolution theorem proving method to reified logics. The logical systems treated include the branching temporal logics and logics of belief based on K and its extensions. Two important problems concerning the application of the resolution rule to reified systems are identified. The first is the redundancy in the representation of truth functional relationships and the second is the axiomatic reasoning about modal structure. Both cause an unnecessary expansion in the search space. We present solutions to both problems which allow the axioms defining the reified logic to be eliminated from the database during theorem proving hence reducing the search space while retaining completeness. We describe three theorem proving methods which embody our solutions and support our analysis with empirical results.

Handling inheritance in a system integrating logic in objects

Abstract The inheritance mechanism of SILO, a system integrating a many-sorted logic within an object-based framework, is presented. In order to be adequate for knowledge representation, it comprises two components, a hardwired and a user-definable. Due to use of typed (sorted) terms, a variety of specialisation types between logical formulas (axioms) are introduced and defined. Thus, the hardwired component is able to represent a variety of inheritance/specialisation relations between objects. The notion of a conflict is defined and conflict detection theorems are introduced. Also, consequence retraction is introduced and used alongside attribute/predicate overriding to resolve conflicts. The user-definable component consists of a number of user definable functions, called meta-functions, which are able to implement both global and local inheritance control. It is based on a partial reflection meta-level architecture.

The inheritance mechanism of a System Integrating Logic in Objects

The inheritance mechanism of SILO, a System Integrating Logic in Objects, is presented. It comprises two components, a hardwired and a user-definable. In the hardwired component, apart from overriding, solution invalidation is also used. The user-definable component consists of a number of user-definable functions to control inheritance, called meta-functions. The architecture employed to realize explicit representation of control knowledge is based on a partial reflection meta-level architecture.<<ETX>>

Neural networks in the study of the brain

Neural networks are models of the brain and have been used within Artificial Intelligence to provide alternative explanations to the symbolic explanations of cognition in which one assumes that an intelligent system has certain explicit representations of some aspect of the world and uses these in intelligent behavior. Obviously, if neural networks are indeed good models of the brain, and give a satisfactory account of cognition, then they could be a valuable tool to neuroscientists. This article gives a brief overview of the various neural network models, and critically reviews their status as models of the brain and of cognition.

STIRDAT: a system tightly integrating relational databases and a theorem prover

Abstract There has been a growing awareness of the need to share data and services among autonomous heterogeneous information sources. For obvious reasons, these sources are storing information in ways that meet their own needs and hence in different formats. However, for a combination of information from heterogeneous sources to be truly useful, a user needs to be able to use the shared information without having to learn the particular data format or the locations of the relevant data. This idea can be taken a step further as the importance of combining techniques from various areas in computer science becomes more obvious. There are a number of benefits that can be derived from combining, for example, some of the features of Artificial Intelligence systems, such as logical inference, with those of traditional database systems. This paper describes STIRDAT, a system tightly and transparently integrating data in a number of relational databases stored at different sites with a theorem prover. It provides a clear illustration of the benefits to be gained from a system combining techniques that have proven independently useful in different areas of Computer Science.