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| 2. |
- Doherty, Patrick, 1957-, et al.
(författare)
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A reduction result for circumscribed semi-horn formulas
- 1996
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Ingår i: Fundamenta Informaticae. - IOS Press. - 0169-2968. ; 28:3,4, s. 261-272
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Tidskriftsartikel (refereegranskat)abstract
- Circumscription has been perceived as an elegant mathematical technique for modeling nonmonotonic and commonsense reasoning, but difficult to apply in practice due to the use of second-order formulas. One proposal for dealing with the computational problems is to identify classes of first-order formulas whose circumscription can be shown to be equivalent to a first-order formula. In previous work, we presented an algorithm which reduces certain classes of second-order circumscription axioms to logically equivalent first-order formulas. The basis for the algorithm is an elimination lemma due to Ackermann. In this paper, we capitalize on the use of a generalization of Ackermann's Lemma in order to deal with a subclass of universal formulas called semi-Horn formulas. Our results subsume previous results by Kolaitis and Papadimitriou regarding a characterization of circumscribed definite logic programs which are first-order expressible. The method for distinguishing which formulas are reducible is based on a boundedness criterion. The approach we use is to first reduce a circumscribed semi-Horn formula to a fixpoint formula which is reducible if the formula is bounded, otherwise not. In addition to a number of other extensions, we also present a fixpoint calculus which is shown to be sound and complete for bounded fixpoint formulas.
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| 3. |
- Doherty, Patrick, 1957-, et al.
(författare)
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A study in modal embeddings of NML3.
- 1996
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Ingår i: Partiality, Modality, and Nonmonotonicity, Studies in Logic, Language and Information.. - CSLI Publications. ; s. 145-168
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Bokkapitel (övrigt vetenskapligt)
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| 4. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Approximate Databases and Query Techniques for Agents with Heterogenous Perceptual Capabilities
- 2004
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Ingår i: Proceedings of the 7th International Conference on Information Fusion. - Mountain View, CA : ISIF. - 91-7056-115-X ; s. 175-182
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a framework that provides software and robotic agents with the ability to ask approximate questions to each other in the context of heterogeneous and contextually limited perceptual capabilities. The framework focuses on situations where agents have varying ability to perceive their environments. These limitations on perceptual capability are formalized using the idea of tolerance spaces. It is assumed that each agent has one or more approximate databases where approximate relations are represented using intuitions from rough set theory. It is shown how sensory and other limitations can be taken into account when constructing approximate databases for each respective agent. Complex relations inherit the approximativeness inherent in the sensors and primitive relations used in their definitions. Agents then query these databases and receive answers through the filters of their perceptual limitations as represented by tolerance spaces and approximate queries. The techniques used are all tractable.
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| 5. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Approximation Transducers and Trees : A Technique for Combining Rough and Crisp Knowledge
- 2003
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Ingår i: Rough-Neural Computing: Techniques for Computing with Words. - Berlin, Heidelberg, New York : Springer. ; s. 189-218
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Bokkapitel (övrigt vetenskapligt)abstract
- This chapter proposes a framework for specifying, constructing, and managing aparticular class of approximate knowledge structures for use with intelligent artifacts rangingfrom simpler devices such as personal digital assistants (PDAs) to more complex ones suchas unmanned aerial vehicles (UAVs). This chapter introduces the notion of an approximationtransducer, which takes approximate relations as input and generates a (possibly moreabstract) approximate relation as output by combining the approximate input relations witha crisp local logical theory representing dependencies between input and output relations.Approximation transducers can be combined to produce approximation trees, which representcomplex approximate knowledge structures characterized by the properties of elaborationtolerance, groundedness in the application domain, modularity, and context dependency.Approximation trees are grounded through the use of primitive concepts generated with supervisedlearning techniques. Changes in definitions of primitive concepts or in the locallogical theories used by transducers result in changes in the knowledge stored in approximationtrees by increasing or decreasing precision in the knowledge qualitatively. Intuitionsand techniques from rough set theory are used to define approximate relations where eachhas an upper and a lower approximation. The constituent components in a rough set havecorrespondences in a logical language used to relate crisp and approximate knowledge. Theinference mechanism associated with the use of approximation trees is based on a generalizationof deductive databases that we call rough relational databases. Approximation trees andqueries to them are characterized in terms of rough relational databases and queries to them.By placing certain syntactic restrictions on the local theories used in transducers, the computationalprocesses used in the query/answering and generation mechanism for approximationtrees remain in PTIME.
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| 6. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Approximative Query Techniques for Agents with Heterogeneous Ontologies and Perceptive Capabilities
- 2004
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Ingår i: Proceedings of the 9th International Conference on the Principles of Knowledge Representation and Reasoning. - Menlo Park, California : AAAI Press. - 978-1-57735-199-3 ; s. 459-468
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a framework that provides software and robotic agents with the ability to ask approximate questions to each other in the context of heterogeneous ontologies and heterogeneous perceptive capabilities.The framework combines the use of logic-based techniques with ideas from approximate reasoning. Initial queries by an agent are transformed into approximate queries using weakest sufficient and strongest necessary conditions on the query and are interpreted as lower and upper approximations on the query. Once the base communication ability is provided, the framework is extended to situations where there is not only a mismatch between agent ontologies, but the agents have varying ability to perceive their environments. This will affect each agent’s ability to ask and interpret results of queries. Limitations on perceptive capability are formalized using the idea of tolerance spaces.
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| 7. |
- Doherty, Patrick, 1957-, et al.
(författare)
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CAKE : A computer aided knowledge engineering technique.
- 2002
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Ingår i: Proceedings of the 15th European Conference on Artificial Intelligence,2002. - IOS Press. ; s. 220-224
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Konferensbidrag (refereegranskat)abstract
- Introduction: Logic engineering often involves the development of modeling tools and inference mechanisms (both standard and non-standard) which are targeted for use in practical applications where expressiveness in representation must be traded off for efficiency in use. Some representative examples of such applications would be the structuring and querying of knowledge on the semantic web, or the representation and querying of epistemic states used with softbots, robots or smart devices. In these application areas, declarative representations of knowledge enhance the functionality of such systems and also provide a basis for insuring the pragmatic properties of modularity and incremental composition. In addition, the mechanisms developed should be tractable, but at the same time, expressive enough to represent such aspects as default reasoning, or approximate or incomplete representations of the environments in which the entities in question are embedded or used, be they virtual or actual. [...]
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| 8. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Circumscribing features and fluents
- 1994
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Ingår i: Temporal Logic : First International Conference, ICTL'94 Bonn, Germany, July 11–14, 1994 Proceedings. - Springer Berlin/Heidelberg. - 3-540-58241-X - 0-387-58241-X ; s. 82-100
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Bokkapitel (övrigt vetenskapligt)abstract
- Sandewall has recently proposed a systematic approach to the representation of knowledge about dynamical systems that includes a general framework in which to assess the range of applicability of existing and new logics for action and change and to provide a means of studying whether and in what sense the logics of action and change are relevant for intelligent agents. As part of the framework, a number of logics of preferential entailment are introduced and assessed for particular classes of action scenario descriptions. This paper provides syntactic characterizations of several of these relations of preferential entailment in terms of standard FOPC and circumscription axioms. The intent is to simplify the process of comparison with existing formalisms which use more traditional techniques and to provide a basis for studying the feasibility of compiling particular classes of problems into logic programs.
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| 9. |
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| 10. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Computing circumscription revisited.
- 1995
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Ingår i: Proceedings of the 14th International Joint Conference on Artificial Intelligence (IJCAI). - 978-1558603639 ; s. 1502-1508
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Konferensbidrag (refereegranskat)
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