| 1. |
- Andersson, Olov, 1979-, et al.
(författare)
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Deep Learning Quadcopter Control via Risk-Aware Active Learning
- 2017
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Ingår i: Proceedings of The Thirty-first AAAI Conference on Artificial Intelligence (AAAI). - : AAAI Press. - 9781577357841 ; , s. 3812-3818
-
Konferensbidrag (refereegranskat)abstract
- Modern optimization-based approaches to control increasingly allow automatic generation of complex behavior from only a model and an objective. Recent years has seen growing interest in fast solvers to also allow real-time operation on robots, but the computational cost of such trajectory optimization remains prohibitive for many applications. In this paper we examine a novel deep neural network approximation and validate it on a safe navigation problem with a real nano-quadcopter. As the risk of costly failures is a major concern with real robots, we propose a risk-aware resampling technique. Contrary to prior work this active learning approach is easy to use with existing solvers for trajectory optimization, as well as deep learning. We demonstrate the efficacy of the approach on a difficult collision avoidance problem with non-cooperative moving obstacles. Our findings indicate that the resulting neural network approximations are least 50 times faster than the trajectory optimizer while still satisfying the safety requirements. We demonstrate the potential of the approach by implementing a synthesized deep neural network policy on the nano-quadcopter microcontroller.
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| 2. |
- Andersson, Olov, 1979-, et al.
(författare)
-
Deep RL for Autonomous Robots: Limitations and Safety Challenges
- 2019
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Konferensbidrag (refereegranskat)abstract
- With the rise of deep reinforcement learning, there has also been a string of successes on continuous control problems using physics simulators. This has lead to some optimism regarding use in autonomous robots and vehicles. However, to successful apply such techniques to the real world requires a firm grasp of their limitations. As recent work has raised questions of how diverse these simulation benchmarks really are, we here instead analyze a popular deep RL approach on toy examples from robot obstacle avoidance. We find that these converge very slowly, if at all, to safe policies. We identify convergence issues on stochastic environments and local minima as problems that warrant more attention for safety-critical control applications.
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| 3. |
- Andersson, Olov, 1979-
(författare)
-
Learning to Make Safe Real-Time Decisions Under Uncertainty for Autonomous Robots
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Robots are increasingly expected to go beyond controlled environments in laboratories and factories, to act autonomously in real-world workplaces and public spaces. Autonomous robots navigating the real world have to contend with a great deal of uncertainty, which poses additional challenges. Uncertainty in the real world accrues from several sources. Some of it may originate from imperfect internal models of reality. Other uncertainty is inherent, a direct side effect of partial observability induced by sensor limitations and occlusions. Regardless of the source, the resulting decision problem is unfortunately computationally intractable under uncertainty. This poses a great challenge as the real world is also dynamic. It will not pause while the robot computes a solution. Autonomous robots navigating among people, for example in traffic, need to be able to make split-second decisions. Uncertainty is therefore often neglected in practice, with potentially catastrophic consequences when something unexpected happens. The aim of this thesis is to leverage recent advances in machine learning to compute safe real-time approximations to decision-making under uncertainty for real-world robots. We explore a range of methods, from probabilistic to deep learning, as well as different combinations with optimization-based methods from robotics, planning and control. Driven by applications in robot navigation, and grounded in experiments with real autonomous quadcopters, we address several parts of this problem. From reducing uncertainty by learning better models, to directly approximating the decision problem itself, all the while attempting to satisfy both the safety and real-time requirements of real-world autonomy.
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| 4. |
- Andersson, Olov, 1979-, et al.
(författare)
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Model-Based Reinforcement Learning in Continuous Environments Using Real-Time Constrained Optimization
- 2015
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Ingår i: Proceedings of the Twenty-Ninth AAAI Conference on Artificial Intelligence (AAAI). - : AAAI Press. - 9781577356981 ; , s. 2497-2503
-
Konferensbidrag (refereegranskat)abstract
- Reinforcement learning for robot control tasks in continuous environments is a challenging problem due to the dimensionality of the state and action spaces, time and resource costs for learning with a real robot as well as constraints imposed for its safe operation. In this paper we propose a model-based reinforcement learning approach for continuous environments with constraints. The approach combines model-based reinforcement learning with recent advances in approximate optimal control. This results in a bounded-rationality agent that makes decisions in real-time by efficiently solving a sequence of constrained optimization problems on learned sparse Gaussian process models. Such a combination has several advantages. No high-dimensional policy needs to be computed or stored while the learning problem often reduces to a set of lower-dimensional models of the dynamics. In addition, hard constraints can easily be included and objectives can also be changed in real-time to allow for multiple or dynamic tasks. The efficacy of the approach is demonstrated on both an extended cart pole domain and a challenging quadcopter navigation task using real data.
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| 5. |
- Andersson, Olov, 1979-, et al.
(författare)
-
Real-Time Robotic Search using Structural Spatial Point Processes
- 2020
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Ingår i: 35TH UNCERTAINTY IN ARTIFICIAL INTELLIGENCE CONFERENCE (UAI 2019). - : Association For Uncertainty in Artificial Intelligence (AUAI). ; , s. 995-1005
-
Konferensbidrag (refereegranskat)abstract
- Aerial robots hold great potential for aiding Search and Rescue (SAR) efforts over large areas, such as during natural disasters. Traditional approaches typically search an area exhaustively, thereby ignoring that the density of victims varies based on predictable factors, such as the terrain, population density and the type of disaster. We present a probabilistic model to automate SAR planning, with explicit minimization of the expected time to discovery. The proposed model is a spatial point process with three interacting spatial fields for i) the point patterns of persons in the area, ii) the probability of detecting persons and iii) the probability of injury. This structure allows inclusion of informative priors from e.g. geographic or cell phone traffic data, while falling back to latent Gaussian processes when priors are missing or inaccurate. To solve this problem in real-time, we propose a combination of fast approximate inference using Integrated Nested Laplace Approximation (INLA), and a novel Monte Carlo tree search tailored to the problem. Experiments using data simulated from real world Geographic Information System (GIS) maps show that the framework outperforms competing approaches, finding many more injured in the crucial first hours.
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| 6. |
- Andersson, Olov, 1979-, et al.
(författare)
-
WARA-PS : a research arena for public safety demonstrations and autonomous collaborative rescue robotics experimentation
- 2021
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Ingår i: Autonomous Intelligent Systems. - : Springer Nature. - 2730-616X. ; 1:1
-
Tidskriftsartikel (refereegranskat)abstract
- A research arena (WARA-PS) for sensing, data fusion, user interaction, planning and control of collaborative autonomous aerial and surface vehicles in public safety applications is presented. The objective is to demonstrate scientific discoveries and to generate new directions for future research on autonomous systems for societal challenges. The enabler is a computational infrastructure with a core system architecture for industrial and academic collaboration. This includes a control and command system together with a framework for planning and executing tasks for unmanned surface vehicles and aerial vehicles. The motivating application for the demonstration is marine search and rescue operations. A state-of-art delegation framework for the mission planning together with three specific applications is also presented. The first one concerns model predictive control for cooperative rendezvous of autonomous unmanned aerial and surface vehicles. The second project is about learning to make safe real-time decisions under uncertainty for autonomous vehicles, and the third one is on robust terrain-aided navigation through sensor fusion and virtual reality tele-operation to support a GPS-free positioning system in marine environments. The research results have been experimentally evaluated and demonstrated to industry and public sector audiences at a marine test facility. It would be most difficult to do experiments on this large scale without the WARA-PS research arena. Furthermore, these demonstrator activities have resulted in effective research dissemination with high public visibility, business impact and new research collaborations between academia and industry.
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| 7. |
- Conte, Gianpaolo, 1974-, et al.
(författare)
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An Integrated UAV Navigation System Based on Aerial Image Matching
- 2008
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Ingår i: IEEE Aerospace Conference 2008,2008. - : IEEE. - 9781424414871 - 9781424414888 ; , s. 3142-3151
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to explore the possibility of using geo-referenced satellite or aerial images to augment an Unmanned Aerial Vehicle (UAV) navigation system in case of GPS failure. A vision based navigation system which combines inertial sensors, visual odometer and registration of a UAV on-board video to a given geo-referenced aerial image has been developed and tested on real flight-test data. The experimental results show that it is possible to extract useful position information from aerial imagery even when the UAV is flying at low altitude. It is shown that such information can be used in an automated way to compensate the drift of the UAV state estimation which occurs when only inertial sensors and visual odometer are used.
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| 8. |
- Conte, Gianpaolo, 1974-, et al.
(författare)
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High Accuracy Ground Target Geo-Location Using Autonomous Micro Aerial Vehicle Platforms
- 2008
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Ingår i: Proceedings of the AIAA Guidance, Navigation, and Control Conference (GNC). - : AIAA. - 9781563479458
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a method for high accuracy ground target localization using a Micro Aerial Vehicle (MAV) equipped with a video camera sensor. The proposed method is based on a satellite or aerial image registration technique. The target geo-location is calculated by registering the ground target image taken from an on-board video camera with a geo- referenced satellite image. This method does not require accurate knowledge of the aircraft position and attitude, therefore it is especially suitable for MAV platforms which do not have the capability to carry accurate sensors due to their limited payload weight and power resources. The paper presents results of a ground target geo-location experiment based on an image registration technique. The platform used is a MAV prototype which won the 3rd US-European Micro Aerial Vehicle Competition (MAV07). In the experiment a ground object was localized with an accuracy of 2.3 meters from a ight altitude of 70 meters.
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| 9. |
- de Leng, Daniel, 1988-
(författare)
-
Robust Stream Reasoning Under Uncertainty
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vast amounts of data are continually being generated by a wide variety of data producers. This data ranges from quantitative sensor observations produced by robot systems to complex unstructured human-generated texts on social media. With data being so abundant, the ability to make sense of these streams of data through reasoning is of great importance. Reasoning over streams is particularly relevant for autonomous robotic systems that operate in physical environments. They commonly observe this environment through incremental observations, gradually refining information about their surroundings. This makes robust management of streaming data and their refinement an important problem.Many contemporary approaches to stream reasoning focus on the issue of querying data streams in order to generate higher-level information by relying on well-known database approaches. Other approaches apply logic-based reasoning techniques, which rarely consider the provenance of their symbolic interpretations. In this work, we integrate techniques for logic-based stream reasoning with the adaptive generation of the state streams needed to do the reasoning over. This combination deals with both the challenge of reasoning over uncertain streaming data and the problem of robustly managing streaming data and their refinement.The main contributions of this work are (1) a logic-based temporal reasoning technique based on path checking under uncertainty that combines temporal reasoning with qualitative spatial reasoning; (2) an adaptive reconfiguration procedure for generating and maintaining a data stream required to perform spatio-temporal stream reasoning over; and (3) integration of these two techniques into a stream reasoning framework. The proposed spatio-temporal stream reasoning technique is able to reason with intertemporal spatial relations by leveraging landmarks. Adaptive state stream generation allows the framework to adapt to situations in which the set of available streaming resources changes. Management of streaming resources is formalised in the DyKnow model, which introduces a configuration life-cycle to adaptively generate state streams. The DyKnow-ROS stream reasoning framework is a concrete realisation of this model that extends the Robot Operating System (ROS). DyKnow-ROS has been deployed on the SoftBank Robotics NAO platform to demonstrate the system's capabilities in a case study on run-time adaptive reconfiguration. The results show that the proposed system - by combining reasoning over and reasoning about streams - can robustly perform stream reasoning, even when the availability of streaming resources changes.
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| 10. |
- de Leng, Daniel, 1988-
(författare)
-
Spatio-Temporal Stream Reasoning with Adaptive State Stream Generation
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A lot of today's data is generated incrementally over time by a large variety of producers. This data ranges from quantitative sensor observations produced by robot systems to complex unstructured human-generated texts on social media. With data being so abundant, making sense of these streams of data through reasoning is challenging. Reasoning over streams is particularly relevant for autonomous robotic systems that operate in a physical environment. They commonly observe this environment through incremental observations, gradually refining information about their surroundings. This makes robust management of streaming data and its refinement an important problem.Many contemporary approaches to stream reasoning focus on the issue of querying data streams in order to generate higher-level information by relying on well-known database approaches. Other approaches apply logic-based reasoning techniques, which rarely consider the provenance of their symbolic interpretations. In this thesis, we integrate techniques for logic-based spatio-temporal stream reasoning with the adaptive generation of the state streams needed to do the reasoning over. This combination deals with both the challenge of reasoning over streaming data and the problem of robustly managing streaming data and its refinement.The main contributions of this thesis are (1) a logic-based spatio-temporal reasoning technique that combines temporal reasoning with qualitative spatial reasoning; (2) an adaptive reconfiguration procedure for generating and maintaining a data stream required to perform spatio-temporal stream reasoning over; and (3) integration of these two techniques into a stream reasoning framework. The proposed spatio-temporal stream reasoning technique is able to reason with intertemporal spatial relations by leveraging landmarks. Adaptive state stream generation allows the framework to adapt in situations in which the set of available streaming resources changes. Management of streaming resources is formalised in the DyKnow model, which introduces a configuration life-cycle to adaptively generate state streams. The DyKnow-ROS stream reasoning framework is a concrete realisation of this model that extends the Robot Operating System (ROS). DyKnow-ROS has been deployed on the SoftBank Robotics NAO platform to demonstrate the system's capabilities in the context of a case study on run-time adaptive reconfiguration. The results show that the proposed system – by combining reasoning over and reasoning about streams – can robustly perform spatio-temporal stream reasoning, even when the availability of streaming resources changes.
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| 11. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
2003 AAAI Spring Symposium Series
- 2003
-
Ingår i: The AI Magazine. - : AAAI Press. - 0738-4602. ; 24:3, s. 131-140
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The American Association for Artificial Intelligence, in cooperation with Stanford University’s Department of Computer Science, presented the 2003 Spring Symposium Series, Monday through Wednesday, 24–26 March 2003, at Stanford University. The titles of the eight symposia were Agent-Mediated Knowledge Management, Computational Synthesis: From Basic Building Blocks to High- Level Functions, Foundations and Applications of Spatiotemporal Reasoning (FASTR), Human Interaction with Autonomous Systems in Complex Environments, Intelligent Multimedia Knowledge Management, Logical Formalization of Commonsense Reasoning, Natural Language Generation in Spoken and Written Dialogue, and New Directions in Question-Answering Motivation.
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| 12. |
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| 13. |
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
A Delegation-Based Architecture for Collaborative Robotics
- 2011
-
Ingår i: Agent-Oriented Software Engineering XI. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642226359 ; , s. 205-247
-
Bokkapitel (refereegranskat)abstract
- Collaborative robotic systems have much to gain by leveraging results from the area of multi-agent systems and in particular agent-oriented software engineering. Agent-oriented software engineering has much to gain by using collaborative robotic systems as a testbed. In this article, we propose and specify a formally grounded generic collaborative system shell for robotic systems and human operated ground control systems. Collaboration is formalized in terms of the concept of delegation and delegation is instantiated as a speech act. Task Specification Trees are introduced as both a formal and pragmatic characterization of tasks and tasks are recursively delegated through a delegation process implemented in the collaborative system shell. The delegation speech act is formally grounded in the implementation using Task Specification Trees, task allocation via auctions and distributed constraint problem solving. The system is implemented as a prototype on Unmanned Aerial Vehicle systems and a case study targeting emergency service applications is presented.
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| 19. |
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| 20. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
A Delegation-Based Cooperative Robotic Framework
- 2011
-
Ingår i: Proceedings of the IEEE International Conference on Robotics and Biomimetic. - : IEEE conference proceedings. - 9781457721366 ; , s. 2955-2962
-
Konferensbidrag (refereegranskat)abstract
- Cooperative robotic systems, such as unmanned aircraft systems, are becoming technologically mature enough to be integrated into civil society. To gain practical use and acceptance, a verifiable, principled and well-defined foundation for interactions between human operators and autonomous systems is needed. In this paper, we propose and specify such a formally grounded collaboration framework. Collaboration is formalized in terms of the concept of delegation and delegation is instantiated as a speech act. Task Specification Trees are introduced as both a formal and pragmatic characterization of tasks and tasks are recursively delegated through a delegation process. The delegation speech act is formally grounded in the implementation using Task Specification Trees, task allocation via auctions and distributed constraint solving. The system is implemented as a prototype on unmanned aerial vehicle systems and a case study targeting emergency service applications is presented.
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| 21. |
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| 22. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
A non-monotonic fuzzy logic.
- 1991
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Ingår i: International Fuzzy Systems Association, Fourth World Congress,1991.
-
Konferensbidrag (refereegranskat)
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| 23. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
A reduction result for circumscribed semi-horn formulas
- 1996
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Ingår i: Fundamenta Informaticae. - : IOS Press. - 0169-2968 .- 1875-8681. ; 28:3,4, s. 261-272
-
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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| 24. |
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| 25. |
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| 26. |
- 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.. - Stanford, California : CSLI Publications. - 1575860317 - 1575860309 ; , s. 145-168
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 27. |
- Doherty, Patrick, 1957-
(författare)
-
A three-valued approach to non-monotonic reasoning
- 1990
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this thesis is the formalization of a type of non-monotonic reasoning using a three-valued logic based on the strong definitions of Kleene. Non-monotonic reasoning is the rule rather than the exception when agents, human or machine, must act where information about the environment is uncertain or incomplete. Information about the environment is subject to change due to external causes, or may simply become outdated. This implies that inferences previously made may no longer hold and in turn must be retracted along with the revision of other information dependent on the retractions. This is the variety of reasoning we would like to find formal models for.We start by extending Kleene-s three-valued logic with an "external negation" connective where ~ a is true when a is false or unknown. In addition, a default operator D is added where D a is interpreted as "a is true by default. The addition of the default operator increases the expressivity of the language, where statements such as "a is not a default" are directly representable. The logic has an intuitive model theoretic semantics without any appeal to the use of a fixpoint semantics for the default operator. The semantics is based on the notion of preferential entailment, where a set of sentences G preferentially entails a sentence a, if and only if a preferred set of the models of G are models of a. We also show that one version of the logic belongs to the class of cumulative non-monotonic formalisms which are a subject of current interest.A decision procedure for the propositional case, based on the semantic tableaux proof method is described and serves as a basis for a QA-system where it can be determined if a sentence a is preferentially entailed by a set of premises G. The procedure is implemented.
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| 28. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
A UAV search and rescue scenario with human body detection and geolocalization
- 2007
-
Ingår i: Proceedings of the 20th Australian Joint Conference on Artificial Intelligence (AI). - : Springer Berlin/Heidelberg. - 9783540769262
-
Konferensbidrag (refereegranskat)abstract
- The use of Unmanned Aerial Vehicles (UAVs) which can operate autonomously in dynamic and complex operational environments is becoming increasingly more common. The UAVTech Lab, is pursuing a long term research endeavour related to the development of future aviation systems which try and push the envelope in terms of using and integrating high-level deliberative or AI functionality with traditional reactive and control components in autonomous UAV systems. In order to carry on such research, one requires challenging mission scenarios which force such integration and development. In this paper, one of these challenging emergency services mission scenarios is presented. It involves search and rescue for injured civilians by UAVs. In leg I of the mission, UAVs scan designated areas and try to identify injured civilians. In leg II of the mission, an attempt is made to deliver medical and other supplies to identified victims. We show how far we have come in implementing and executing such a challenging mission in realistic urban scenarios.
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| 29. |
- Doherty, Patrick, 1957-
(författare)
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Advanced Research with Autonomous Unmanned Aerial Vehicles
- 2004
-
Ingår i: Proceedings of the 9th International Conference on the Principles of Knowledge Representation and Reasoning. - Menlo Park, CA : AAAI Press. - 9781577351993 ; , s. 731-732
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The emerging area of intelligent unmanned aerial vehicle (UAV) research has shown rapid development in recent years and offers a great number of research challenges for artificial intelligence and knowledge representation. For both military and civilian applications, there is a desire to develop more sophisticated UAV platforms where the emphasis is placed on intelligent capabilities and their integration in complex distributed software architectures. Such architectures should support the integration of deliberative, reactive and control functionalities in addition to the UAV’s integration with larger network centric systems. In my talk I will present some of the research and results from a long term basic research project with UAVs currently being pursued at Linköping University, Sweden. The talk will focus on knowledge representation techniques used in the project and the support for these techniques provided by the software architecture developed for our UAV platform, a Yamaha RMAX helicopter. Additional focus will be placed on some of the planning and execution monitoring functionality developed for our applications in the areas of traffic monitoring, surveying and photogrammetry and emergency services assistance.
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| 30. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Approximate Databases : A support tool for approximate reasoning
- 2006
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Ingår i: Journal of applied non-classical logics. - : Éditions Hermès-Lavoisier. - 1166-3081 .- 1958-5780. ; 16:1-2, s. 87-118
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes an experimental platform for approximate knowledge databases called the Approximate Knowledge Database (AKDB), based on a semantics inspired by rough sets. The implementation is based upon the use of a standard SQL database to store logical facts, augmented with several query interface layers implemented in JAVA through which extensional, intensional and local closed world nonmonotonic queries in the form of crisp or approximate logical formulas can be evaluated tractably. A graphical database design user interface is also provided which simplifies the design of databases, the entering of data and the construction of queries. The theory and semantics for AKDBs is presented in addition to application examples and details concerning the database implementation.
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| 31. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Approximate Databases and Query Techniques for Agents with Heterogenous Perceptual Capabilities
- 2004
-
Ingår i: Proceedings of the 7th International Conference on Information Fusion. - Mountain View, CA : ISIF. - 917056115X ; , s. 175-182
-
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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| 32. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Approximation Transducers and Trees : A Technique for Combining Rough and Crisp Knowledge
- 2004
-
Ingår i: Rough-Neural Computing: Techniques for Computing with Words. - Berlin, Heidelberg, New York : Springer. - 9783540430599 - 3540430598 ; , s. 189-218
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Soft computing comprises various paradigms dedicated to approximately solving real-world problems, e.g., in decision making, classification or learning; among these paradigms are fuzzy sets, rough sets, neural networks, and genetic algorithms.It is well understood now in the soft computing community that hybrid approaches combining various paradigms provide very promising attempts to solving complex problems. Exploiting the potential and strength of both neural networks and rough sets, this book is devoted to rough-neurocomputing which is also related to the novel aspect of computing based on information granulation, in particular to computing with words. It provides foundational and methodological issues as well as applications in various fields.
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| 33. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Approximative Query Techniques for Agents with Heterogeneous Ontologies and Perceptive Capabilities
- 2004
-
Ingår i: Proceedings of the 9th International Conference on the Principles of Knowledge Representation and Reasoning. - Menlo Park, California : AAAI Press. - 9781577351993 ; , s. 459-468
-
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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| 34. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
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
-
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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| 35. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Circumscribing features and fluents
- 1994
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Ingår i: Temporal Logic. - Berlin/New York : Springer Berlin/Heidelberg. - 354058241X - 038758241X ; , s. 82-100
-
Bokkapitel (refereegranskat)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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| 36. |
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| 37. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Computing circumscription revisited : A reduction algorithm.
- 1994
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, a great deal of attention has been devoted to logics of "commonsense" reasoning. Among the candidates proposed, circumscription has been perceived as an elegant mathematical technique for modeling nonmonotonic reasoning, but difficult to apply in practice. The major reason for this is the nd-order nature of circumscription axioms and the difficulty in finding proper substitutions of predicate expressions for predicate variables. One solution to this problem is to compile, where possible, nd-order formulas into equivalent 1st-order formulas. Although some progress has been made using this approach, the results are not as strong as one might desire and they are isolated in nature. In this article, we provide a general method which can be used in an algorithmic manner to reduce circumscription axioms to 1st-order formulas. The algorithm takes as input an arbitrary 2nd-order formula and either returns as output an equivalent 1st-order formula, or terminates with failure. The class of 2nd-order formulas, and analogously the class of circumscriptive theories which can be reduced, provably subsumes those covered by existing results. We demonstrate the generality of the algorithm using circumscriptive theories with mixed quantifiers (some involving Skolemization), variable constants, non-separated formulas, and formulas with n-ary predicate variables. In addition, we analyze the strength of the algorithm and compare it with existing approaches providing formal subsumption results.
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| 38. |
- 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). - 9781558603639 ; , s. 1502-1508
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Konferensbidrag (refereegranskat)
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| 39. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Computing circumscription revisited : A reduction algorithm
- 1997
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Ingår i: Journal of automated reasoning. - : Kluwer Academic Publishers. - 0168-7433 .- 1573-0670. ; 18:3, s. 297-336
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, a great deal of attention has been devoted to logics of common-sense reasoning. Among the candidates proposed, circumscription has been perceived as an elegant mathematical technique for modeling nonmonotonic reasoning, but difficult to apply in practice. The major reason for this is the second-order nature of circumscription axioms and the difficulty in finding proper substitutions of predicate expressions for predicate variables. One solution to this problem is to compile, where possible, second-order formulas into equivalent first-order formulas. Although some progress has been made using this approach, the results are not as strong as one might desire and they are isolated in nature. In this article, we provide a general method that can be used in an algorithmic manner to reduce certain circumscription axioms to first-order formulas. The algorithm takes as input an arbitrary second-order formula and either returns as output an equivalent first-order formula, or terminates with failure. The class of second-order formulas, and analogously the class of circumscriptive theories that can be reduced, provably subsumes those covered by existing results. We demonstrate the generality of the algorithm using circumscriptive theories with mixed quantifiers (some involving Skolemization), variable constants, nonseparated formulas, and formulas with n-ary predicate variables. In addition, we analyze the strength of the algorithm, compare it with existing approaches, and provide formal subsumption results.
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| 40. |
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| 41. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Computing strongest necessary and weakest sufficient conditions of first-order formulas
- 2001
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Ingår i: 17th International Joint Conference on Artificial Intelligence,2001. - San Francisco, CA, USA : Morgan Kaufmann Publishers Inc.. - 1558608125 - 9781558608122 ; , s. 145-151
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Konferensbidrag (refereegranskat)abstract
- A technique is proposed for computing the weakest sufficient (wsc) and strongest necessary (snc) conditions for formulas in an expressive fragment of first-order logic using quantifier elimination techniques. The efficacy of the approach is demonstrated by using the techniques to compute snc's and wsc's for use in agent communication applications, theory approximation and generation of abductive hypotheses. Additionally, we generalize recent results involving the generation of successor state axioms in the propositional situation calculus via snc's to the first-order case. Subsumption results for existing approaches to this problem and a re-interpretation of the concept of forgetting as a process of quantifier elimination are also provided.
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| 42. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Declarative PTIME queries for relational databases using quantifier elimination
- 1999
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Ingår i: Journal of logic and computation (Print). - : Oxford University Press. - 0955-792X .- 1465-363X. ; 9:5, s. 737-758
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider the problem of expressing and computing queries on relational deductive databases in a purely declarative query language, called SHQL (Semi-Horn Query Language). Assuming the relational databases in question are ordered, we show that all SHQL queries are computable in PTIME (polynomial time) and the whole class of PTIME queries is expressible in SHQL. Although similar results have been proven for fixpoint languages and extensions to datalog, the claim is that SHQL has the advantage of being purely declarative, where the negation operator is interpreted as classical negation, mixed quantifiers may be used and a query is simply a restricted first-order theory not limited by the rule-based syntactic restrictions associated with logic programs in general. We describe the PTIME algorithm used to compute queries in SHQL which is based in part on quantifier elimination techniques and also consider extending the method to incomplete relational databases using intuitions related to circumscription techniques.
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| 43. |
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| 44. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Defaults as first-class citizens
- 1992
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Ingår i: Proceedings of the 22nd International Symposium on Multiple-Valued Logic (SMVL). - : IEEE Computer Society. - 0818626801 ; , s. 146-154
-
Konferensbidrag (refereegranskat)abstract
- A nonmonotonic logic with explicit defaults, NML3, is presented. It is characterized by the following features: (1) the use of the strong Kleene three-valued logic as a basis; (2) the addition of an explicit default operator which enables distinguishing tentative conclusions from ordinary conclusions in the object language; and (3) the use of the idea of preferential entailment to generate nonmonotonic behavior. The central feature of the formalism, the use of an explicit default operator with a model-theoretic semantics based on the notion of a partial interpretation, distinguishes NML3 from most previous formalisms. By capitalizing on the distinction between tentative and ordinary conclusions, NML3 provides increased expressibility in comparison to many of the standard nonmonotonic formalisms and greater flexibility in the representation of subtle aspects of default reasoning. This is shown through examples.
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| 45. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Delayed effects of actions = direct effects + causal rules
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We propose an approach to modeling delayed effects of actions which is based on the use of causal constraints and their interaction with the direct effects of actions. The approach extends previous work with a causal approach used to deal with the ramification problem. We show the similarity between solutions to the modeling of indirect effects and delayed effects of actions by example. The base logic PMON+ is a temporal logic for reasoning about action and change and uses circumscription. It is shown that the extension for delayed effects of actions retains the first-order reducibility property shown previously for successfully dealing with the frame and ramification problems for a large class of action scenarios. We also consider the “causal qualification” problem, "natural death" of fluents and causal lag, each of which is closely related to the use of delayed effects.
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| 46. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Delegation-Based Collaboration
- 2012
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Ingår i: Proceedings of the 5th International Conference on Cognitive Systems (CogSys).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 47. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Distinguishing between facts and default assumptions.
- 1992
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Ingår i: Non-Monotonic Reasoning and Partial Semantics. Ellis Horwood Workshops.. - New York : Ellis Horwood Ltd.. - 0136251463 - 9780136251460
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 48. |
- Doherty, Patrick, 1957-, et al.
(författare)
-
Dynamics of approximate information fusion
- 2007
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Ingår i: Proceedings of the International Conference on Rough Sets and Emerging Intelligent Systems Paradigms (RSEISP). - Heidelberg, Germany : Springer Berlin/Heidelberg. - 9783540734505 ; , s. 668-677
-
Konferensbidrag (refereegranskat)abstract
- The multi-agent system paradigm has proven to be a useful means of abstraction when considering distributed systems with interacting components. It is often the case that each component may be viewed as an intelligent agent with specific and often limited perceptual capabilities. It is also the case that these agent components may be used as information sources and such sources may be aggregated to provide global information about particular states, situations or activities in the embedding environment. This paper investigates a framework for information fusion based on the use of generalizations of rough set theory and the use of dynamic logic as a basis for aggregating similarity relations among objects where the similarity relations represent individual agents perceptual capabilities or limitations. As an added benefit, it is shown how this idea may also be integrated into description logics.
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| 49. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Efficient reasoning using the local closed-world assumption
- 2000
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Ingår i: Proceedings of the 9th International Conference on Artificial Intelligence: Methodology, Systems and Applications (AIMSA). - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540410447 - 9783540453314 ; , s. 49-58
-
Konferensbidrag (refereegranskat)abstract
- We present a sound and complete, tractable inference method for reasoning with localized closed world assumptions (LCWA’s) which can be used in applications where a reasoning or planning agent can not assume complete information about planning or reasoning states. This Open World Assumption is generally necessary in most realistic robotics applications. The inference procedure subsumes that described in Etzioni et al [9], and others. In addition, it provides a great deal more expressivity, permitting limited use of negation and disjunction in the representation of LCWA’s, while still retaining tractability. The ap- proach is based on the use of circumscription and quantifier elimination techniques and inference is viewed as querying a deductive database. Both the preprocessing of the database using circumscription and quan- tifier elimination, and the inference method itself, have polynomial time and space complexity.
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| 50. |
- Doherty, Patrick, 1957-, et al.
(författare)
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Explaining explanation closure
- 1996
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Ingår i: Proceedings of the 9th International Symposium on Methodologies for Intelligent Systems,1996. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 3540612866 ; , s. 521-530
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Konferensbidrag (refereegranskat)abstract
- Recently, Haas, Schubert, and Reiter, have developed an alternative approach to the frame problem which is based on the idea of using explanation closure axioms. The claim is that there is a monotonic solution for characterizing nonchange in serial worlds with fully specified actions, where one can have both a succinct representation of frame axioms and an effective proof theory for the characterization. In the paper, we propose a circumscriptive version of explanation closure, PMON, that has an effective proof theory and works for both context dependent and nondeterministic actions. The approach retains representational succinctness and a large degree of elaboration tolerance, since the process of generating closure axioms is fully automated and is of no concern to the knowledge engineer. In addition, we argue that the monotonic/nonmonotonic dichotomy proposed by others is not as sharp as previously claimed and is not fully justified.
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