We consider the problem of integrating Reiter's default logic into terminological representation systems. It turns out that such an integration is less straightforward than we expected, considering the fact that the terminological language is a decidable sublanguage of first-order logic. Semantically, one has the unpleasant effect that the consequences of a terminological default theory may be rather unintuitive, and may even vary with the syntactic structure of equivalent concept expressions. This is due to the unsatisfactory treatment of open defaults via Skolemization in Reiter's semantics. On the algorithmic side, we show that this treatment may lead to an undecidable default consequence relation, even though our base language is decidable, and we have only finitely many (open) defaults. Because of these problems, we then consider a restricted semantics for open defaults in our terminological default theories: default rules are only applied to individuals that are explicitly presen...

Knowledge representation languages invariably reflect a trade-off between expressivity and tractability. Evidence suggests that the compromise chosen by description logics is a particularly successful one. However, description logic (as for all variants of first-order logic) is severely limited in its ability to express uncertainty. In this paper, we present P-CLASSIC, a probabilistic version of the description logic CLASSIC. In addition to terminological knowledge, the language utilizes Bayesian networks to express uncertainty about the basic properties of an individual, the number of fillers for its roles, and the properties of these fillers. We provide a semantics for P-CLASSIC and an effective inference procedure for probabilistic subsumption: computing the probability that a random individual in class C is also in class D. The effectiveness of the algorithm relies on independenceassumptions and on our ability to execute lifted inference: reasoning about similar individuals as a gr...

In a recent paper we have proposed terminological default logic as a formalism which combines both means for structured representation of classes and objects, and for default inheritance of properties. The major drawback which terminological default logic inherits from general default logic is that it does not take precedence of more specific defaults over more general ones into account. This behaviour has already been criticized in the general context of default logic, but it is all the more problematic in the terminological case where the emphasis lies on the hierarchical organization of concepts. The present paper addresses the problem of modifying terminological default logic such that more specific defaults are preferred. It turns out that the existing approaches for expressing priorities between defaults do not seem to be appropriate for this purpose. Therefore we shall consider an alternative approach for dealing with prioritization in the framework of Reiter's def...

In this paper, we construct a new concept description language intended for representing dynamic and intensional knowledge. The most important feature distinguishing this language from its predecessors in the literature is that it allows applications of modal operators to all kinds of syntactic terms: concepts, roles and formulas. Moreover, the language may contain both local (i.e., state-dependent) and global (i.e., state-independent) concepts, roles and objects. All this provides us with the most complete and natural means for re ecting the dynamic and intensional behaviour of application domains. We construct a satis ability checking (mosaic-type) algorithm for this language (based on ALC) in(i) arbitrary multimodal frames, (ii) frames with universal accessibility relations (for knowledge) and (iii) frames with transitive, symmetrical and euclidean relations (for beliefs). On the other hand, it is shown that the satisfaction problem becomes undecidable if the underlying frames are arbitrary strict linear orders, hN; <i, or the language contains the common knowledge operator for n 2 agents. 1

This paper addresses issues in visual language theory with the help of logic formalisms that were developed for reasoning tasks by the artificial intelligence and spatial databases community, especially for spatial and diagrammatical reasoning. We describe an approach based on three formal components. Topology is used to define basic geometric objects. Theory about spatial relations from the domain of spatial databases is employed to define possible relationships between visual language elements. Description logic theory from the AI community is used to combine topology and spatial relations. The resulting theory has been successfully applied to formally specifying semantics of visual languages. The theory’s application is illustrated with a specification of entity-relationship diagrams. 1

The Frame-logic (F-logic) approach of [20] is suggested as an underlying framework for description languages. F-logic is shown to provide a full account for description languages, without losing the direct semantics and the descriptive nature. It can support such desirable features as high order role fillers, collective entities, intensions, roles as first class objects and n-ary relationships. Yet, its semantics is first order. In an F-logic based description language, few description constructs are built in, and concepts, roles, and terminological operators are definable. Discussion of desirable features in descriptions is made possible within a single, uniform framework, that also coherently integrates with logic programming and deductive, object-oriented database technology. Typical descriptive operators can be defined in the language, thereby yielding a flexible description language, in which not all operators must be built in. keywords: object-oriented representation, F-logic, de...

Software agents are computer programs that act on behalf of users to perform routine, tedious, and timeconsuming tasks. To be useful to an individual user, an agent must be personalized to his or her goals, habits, and preferences. We have created an enduser programming system that makes it easy for users to state rules for their agents to follow. The main advance over previous approaches is that the system automatically determines conflicts between rules and guides users in resolving the conflicts. Thus, over time, user and system collaborate in developing a set of rules that embody the user's preferences for handling a wide variety of situations. KEYWORDS agents, end-user programming, intelligent systems INTRODUCTION Software agents are the focus of much interest in the popular press and are a hot research topic in humancomputer interaction [3,5,7,8,9,10,11,13], artificial intelligence [17], and distributed computing [16]. HCI research on agents can be distinguished by its user-c...

Large knowledge bases that are intended for applications such as CAD, corporate repositories or process control will have to be shared by multiple users. For these systems to scale up, to give acceptable performance and to exhibit consistent behavior, it is mandatory to synchronize user transactions using a concurrency control algorithm. The transactions in knowledge bases often access a large number of entities and perform complex inferences that may last for a long period of time. In such a situation, using conventional concurrency control methods, which require a transaction to hold its locks until it has acquired all the locks it will ever need, do not lead to good performance. This thesis examines the problem of concurrency control for such long transactions in a knowledge base setting. Using a directed graph as a general model of a knowledge base, we develop an algorithm, called the Dynamic Directed Graph (DDG) policy, that allows release of locks by a transaction before it has ...

This paper first explores the knowledge management problem in more detail and discuss challenges to acquiring, maintaining, and disseminating design knowledge. We then describe a framework for integrating a design memory tool Human-Computer Interaction, , 10, 1 (1995), 1-38.

Practical applications of description logics (DLs) in knowledge-based systems have forced us to introduce the following features which are absent from existing DLs: ffl allowing a concept to be regarded at the same time as an individual (the instance of some other meta-level concept) ffl allowing an individual to represent a collection (set) of other individuals. The first extension, called concept reification, is more general and thus can cover the second one too. We argue that the absence of these features from existing DLs is an important reason for the lack of a unified approach to description logics and object-oriented databases. We also show that concept reification cannot be dealt with by the standard DL semantics and propose a slightly modified semantics that takes care of the inherent higher-order features of reification in a first-order setting. A sound and complete inference algorithm for checking consistency in reified ALCO2 knowledge bases is subsequently put forward. ...