Hide abstracts BibTeX entries  
2015  
[33] 
2015. Efficient Processing of Simple Temporal Networks with Uncertainty: Algorithms for Dynamic Controllability Verification. Temporal formalisms are essential for reasoning about actions that are carried out over time. The exact durations of such actions are generally hard to predict. In temporal planning, the resulting uncertainty is often worked around by only considering upper bounds on durations, with the assumption that when an action happens to be executed more quickly, the plan will still succeed. However, this assumption is often false: If we finish cooking too early, the dinner will be cold before everyone is ready to eat. Using <em>Simple Temporal Networks with Uncertainty (STNU)</em>, a planner can correctly take both lower and upper duration bounds into account. It must then verify that the plans it generates are executable regardless of the actual outcomes of the uncertain durations. This is captured by the property of <em>dynamic controllability</em> (DC), which should be verified incrementally during plan generation. Recently a new incremental algorithm for verifying dynamic controllability was proposed: <em>EfficiantIDC</em>, which can verify if an STNU that is DC remains DC after the addition or tightening of a constraint (corresponding to a new action being added to a plan). The algorithm was shown to have a worst case complexity of O(n<sup>4</sup>) for each addition or tightening. This can be amortized over the construction of a whole STNU for an amortized complexity in O(n<sup>3</sup>). In this paper we improve the <em>EfficientIDC</em> algorithm in a way that prevents it from having to reprocess nodes. This improvement leads to a lower worst case complexity in O(n<sup>3</sup>). 
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2014  
[32] 
2014. Evaluation of a Lightweight Lidar and a Photogrammetric System for Unmanned Airborne Mapping Applications: [Bewertung eines Lidarsystems mit geringem Gewicht und eines photogrammetrischen Systems fÃ¼r Anwendungen auf einem UAV]. Photogrammetrie  Fernerkundung  Geoinformation, ??(4):287–298. E. Schweizerbart'sche Verlagsbuchhandlung. Link to article: http://www.ingentaconnect.com/content/sc... This paper presents a comparison of two lightweight and lowcost airborne mapping systems. One is based on a lidar technology and the other on a video camera. The airborne lidar system consists of a highprecision global navigation satellite system (GNSS) receiver, a microelectromechanical system (MEMS) inertial measurement unit, a magnetic compass and a lowcost lidar scanner. The vision system is based on a consumer grade video camera. A commercial photogrammetric software package is used to process the acquired images and generate a digital surface model. The two systems are described and compared in terms of hardware requirements and data processing. The systems are also tested and compared with respect to their application on board of an unmanned aerial vehicle (UAV). An evaluation of the accuracy of the two systems is presented. Additionally, the multi echo capability of the lidar sensor is evaluated in a test site covered with dense vegetation. The lidar and the camera systems were mounted and tested onboard an industrial unmanned helicopter with maximum takeoff weight of around 100 kilograms. The presented results are based on real flighttest data. 
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2013  
[31] 
2013. Automated Generation of Logical Constraints on Approximation Spaces Using Quantifier Elimination. Fundamenta Informaticae, 127(14):135–149. IOS Press. DOI: 10.3233/FI2013900. Note: Funding AgenciesSwedish Research Council (VR) Linnaeus Center CADICSELLIIT Excellence Center at LinkopingLund in Information TechnologyCUAS projectSSF, the Swedish Foundation for Strategic Research This paper focuses on approximate reasoning based on the use of approximation spaces. Approximation spaces and the approximated relations induced by them are a generalization of the rough setbased approximations of Pawlak. Approximation spaces are used to define neighborhoods around individuals and rough inclusion functions. These in turn are used to define approximate sets and relations. In any of the approaches, one would like to embed such relations in an appropriate logical theory which can be used as a reasoning engine for specific applications with specific constraints. We propose a framework which permits a formal study of the relationship between properties of approximations and properties of approximation spaces. Using ideas from correspondence theory, we develop an analogous framework for approximation spaces. We also show that this framework can be strongly supported by automated techniques for quantifier elimination. 
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[30] 
2013. Highlevel Mission Specification and Planning for Collaborative Unmanned Aircraft Systems using Delegation. Unmanned Systems, 1(1):75–119. World Scientific. Automated specification, generation and execution of high level missions involving one or more heterogeneous unmanned aircraft systems is in its infancy. Much previous effort has been focused on the development of air vehicle platforms themselves together with the avionics and sensor subsystems that implement basic navigational skills. In order to increase the degree of autonomy in such systems so they can successfully participate in more complex mission scenarios such as those considered in emergency rescue that also include ongoing interactions with human operators, new architectural components and functionalities will be required to aid not only human operators in mission planning, but also the unmanned aircraft systems themselves in the automatic generation, execution and partial verification of mission plans to achieve mission goals. This article proposes a formal framework and architecture based on the unifying concept of delegation that can be used for the automated specification, generation and execution of highlevel collaborative missions involving one or more air vehicles platforms and human operators. We describe an agentbased software architecture, a temporal logic based mission specification language, a distributed temporal planner and a task specification language that when integrated provide a basis for the generation, instantiation and execution of complex collaborative missions on heterogeneous air vehicle systems. A prototype of the framework is operational in a number of autonomous unmanned aircraft systems developed in our research lab. 
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[29] 
2013. StreamBased Hierarchical Anchoring. Autonomous systems situated in the real world often need to recognize, track, and reason about various types of physical objects. In order to allow reasoning at a symbolic level, one must create and continuously maintain a correlation between symbols denoting physical objects and sensor data being collected about them, a process called anchoring.In this paper we present a streambased hierarchical anchoring framework. A classification hierarchy is associated with expressive conditions for hypothesizing the type and identity of an object given streams of temporally tagged sensor data. The anchoring process constructs and maintains a set of object linkage structures representing the best possible hypotheses at any time. Each hypothesis can be incrementally generalized or narrowed down as new sensor data arrives. Symbols can be associated with an object at any level of classification, permitting symbolic reasoning on different levels of abstraction. The approach is integrated in the DyKnow knowledge processing middleware and has been applied to an unmanned aerial vehicle traffic monitoring application. 
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2011  
[28] 
2011. Reports of the AAAI 2011 Spring Symposia. The AI Magazine, 32(3):119–127. AAAI Press. The Association for the Advancement of Artificial Intelligence presented the 2011 Spring Symposium Series Monday through Wednesday, March 2123, 2011, at Stanford University. This report summarizes the eight symposia. 
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2010  
[27] 
2010. Optimal placement of UVbased communications relay nodes. Journal of Global Optimization, 48(4):511–531. Springer. DOI: 10.1007/s1089801095268. Note: The original publication is available at www.springerlink.com:Oleg Burdakov, Patrick Doherty, Kaj Holmberg and PerMagnus Olsson, Optimal placement of UVbased communications relay nodes, 2010, Journal of Global Optimization, (48), 4, 511531.http://dx.doi.org/10.1007/s1089801095268Copyright: Springer Science Business Mediahttp://www.springerlink.com/ We consider a constrained optimization problem with mixed integer and real variables. It models optimal placement of communications relay nodes in the presence of obstacles. This problem is widely encountered, for instance, in robotics, where it is required to survey some target located in one point and convey the gathered information back to a base station located in another point. One or more unmanned aerial or ground vehicles (UAVs or UGVs) can be used for this purpose as communications relays. The decision variables are the number of unmanned vehicles (UVs) and the UV positions. The objective function is assumed to access the placement quality. We suggest one instance of such a function which is more suitable for accessing UAV placement. The constraints are determined by, firstly, a free line of sight requirement for every consecutive pair in the chain and, secondly, a limited communication range. Because of these requirements, our constrained optimization problem is a difficult multiextremal problem for any fixed number of UVs. Moreover, the feasible set of real variables is typically disjoint. We present an approach that allows us to efficiently find a practically acceptable approximation to a global minimum in the problem of optimal placement of communications relay nodes. It is based on a spatial discretization with a subsequent reduction to a shortest path problem. The case of a restricted number of available UVs is also considered here. We introduce two label correcting algorithms which are able to take advantage of using some peculiarities of the resulting restricted shortest path problem. The algorithms produce a Pareto solution to the twoobjective problem of minimizing the path cost and the number of hops. We justify their correctness. The presented results of numerical 3D experiments show that our algorithms are superior to the conventional BellmanFord algorithm tailored to solving this problem. 
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[26] 
2010. Relay Positioning for Unmanned Aerial Vehicle Surveillance. The international journal of robotics research, 29(8):1069–1087. Sage Publications. DOI: 10.1177/0278364910369463. When unmanned aerial vehicles (UAVs) are used for surveillance, information must often be transmitted to a base station in real time. However, limited communication ranges and the common requirement of free line of sight may make direct transmissions from distant targets impossible. This problem can be solved using relay chains consisting of one or more intermediate relay UAVs. This leads to the problem of positioning such relays given known obstacles, while taking into account a possibly missionspecific quality measure. The maximum quality of a chain may depend strongly on the number of UAVs allocated. Therefore, it is desirable to either generate a chain of maximum quality given the available UAVs or allow a choice from a spectrum of Paretooptimal chains corresponding to different tradeoffs between the number of UAVs used and the resulting quality. In this article, we define several problem variations in a continuous threedimensional setting. We show how sets of Paretooptimal chains can be generated using graph search and present a new labelcorrecting algorithm generating such chains significantly more efficiently than the bestknown algorithms in the literature. Finally, we present a new dual ascent algorithm with better performance for certain tasks and situations. 
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[25] 
2010. Bridging the sensereasoning gap: DyKnow  Streambased middleware for knowledge processing. Engineering autonomous agents that display rational and goaldirected behavior in dynamic physical environments requires a steady flow of information from sensors to highlevel reasoning components. However, while sensors tend to generate noisy and incomplete quantitative data, reasoning often requires crisp symbolic knowledge. The gap between sensing and reasoning is quite wide, and cannot in general be bridged in a single step. Instead, this task requires a more general approach to integrating and organizing multiple forms of information and knowledge processing on different levels of abstraction in a structured and principled manner. We propose knowledge processing middleware as a systematic approach to organizing such processing. Desirable properties are presented and motivated. We argue that a declarative streambased system is appropriate for the required functionality and present DyKnow, a concrete implemented instantiation of streambased knowledge processing middleware with a formal semantics. Several types of knowledge processes are defined and motivated in the context of a UAV traffic monitoring application. In the implemented application, DyKnow is used to incrementally bridge the sensereasoning gap and generate partial logical models of the environment over which metric temporal logical formulas are evaluated. Using such formulas, hypotheses are formed and validated about the type of vehicles being observed. DyKnow is also used to generate event streams representing for example changes in qualitative spatial relations, which are used to detect traffic violations expressed as declarative chronicles. 
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2009  
[24] 
2009. A Temporal Logicbased Planning and Execution Monitoring Framework for Unmanned Aircraft Systems. Research with autonomous unmanned aircraft systems is reaching a new degree of sophistication where targeted missions require complex types of deliberative capability integrated in a practical manner in such systems. Due to these pragmatic constraints, integration is just as important as theoretical and applied work in developing the actual deliberative functionalities. In this article, we present a temporal logicbased task planning and execution monitoring framework and its integration into a fully deployed rotorbased unmanned aircraft system developed in our laboratory. We use a very challenging emergency services application involving body identification and supply delivery as a vehicle for showing the potential use of such a framework in realworld applications. TALplanner, a temporal logicbased task planner, is used to generate mission plans. Building further on the use of TAL (Temporal Action Logic), we show how knowledge gathered from the appropriate sensors during plan execution can be used to create state structures, incrementally building a partial logical model representing the actual development of the system and its environment over time. We then show how formulas in the same logic can be used to specify the desired behavior of the system and its environment and how violations of such formulas can be detected in a timely manner in an execution monitor subsystem. The pervasive use of logic throughout the higher level deliberative layers of the system architecture provides a solid shared declarative semantics that facilitates the transfer of knowledge between different modules. 
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[23] 
2009. VisionBased Unmanned Aerial Vehicle Navigation Using GeoReferenced Information. EURASIP Journal on Advances in Signal Processing, 2009(387308):1–18. Hindawi Publishing Corporation. DOI: 10.1155/2009/387308. This paper investigates the possibility of augmenting an Unmanned Aerial Vehicle (UAV) navigation system with a passive video camera in order to cope with longterm GPS outages. The paper proposes a visionbased navigation architecture which combines inertial sensors, visual odometry, and registration of the onboard video to a georeferenced aerial image. The visionaided navigation system developed is capable of providing highrate and driftfree state estimation for UAV autonomous navigation without the GPS system. Due to the use of imagetomap registration for absolute position calculation, driftfree position performance depends on the structural characteristics of the terrain. Experimental evaluation of the approach based on offline flight data is provided. In addition the architecture proposed has been implemented onboard an experimental UAV helicopter platform and tested during visionbased autonomous flights. 
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2007  
[22] 
2007. Communication between agents with heterogeneous perceptual capabilities. In real world applications robots and software agents often have to be equipped with higher level cognitive functions that enable them to reason, act and perceive in changing, incompletely known and unpredictable environments. One of the major tasks in such circumstances is to fuse information from various data sources. There are many levels of information fusion, ranging from the fusing of low level sensor signals to the fusing of high level, complex knowledge structures. In a dynamically changing environment even a single agent may have varying abilities to perceive its environment which are dependent on particular conditions. The situation becomes even more complex when different agents have different perceptual capabilities and need to communicate with each other. In this paper, we propose a framework that provides agents with the ability to fuse both low and high level approximate knowledge in the context of dynamically changing environments while taking account of heterogeneous and contextually limited perceptual capabilities. To model limitations on an agent's perceptual capabilities we introduce the idea of partial tolerance spaces. We assume that each agent has one or more approximate databases where approximate relations are represented using lower and upper approximations on sets. Approximate relations are generalizations of rough sets. It is shown how sensory and other limitations can be taken into account when constructing and querying approximate databases for each respective agent. Complex relations inherit the approximativeness of primitive relations used in their definitions. Agents then query these databases and receive answers through the filters of their perceptual limitations as represented by (partial) tolerance spaces and approximate queries. The techniques used are all tractable. Â© 2005 Elsevier B.V. All rights reserved. 
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[21] 
2007. A correspondence framework between threevalued logics and similaritybased approximate reasoning. Fundamenta Informaticae, 75(14):179–193. IOS Press. This paper focuses on approximate reasoning based on the use of similarity spaces. Similarity spaces and the approximated relations induced by them are a generalization of the rough setbased approximations of Pawlak [17, 18]. Similarity spaces are used to define neighborhoods around individuals and these in turn are used to define approximate sets and relations. In any of the approaches, one would like to embed such relations in an appropriate logic which can be used as a reasoning engine for specific applications with specific constraints. We propose a framework which permits a formal study of the relationship between approximate relations, similarity spaces and threevalued logics. Using ideas from correspondence theory for modal logics and constraints on an accessibility relation, we develop an analogous framework for threevalued logics and constraints on similarity relations. In this manner, we can provide a tool which helps in determining the proper threevalued logical reasoning engine to use for different classes of approximate relations generated via specific types of similarity spaces. Additionally, by choosing a threevalued logic first, the framework determines what constraints would be required on a similarity relation and the approximate relations induced by it. Such information would guide the generation of approximate relations for specific applications. 
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2006  
[20] 
2006. A flexible runtime system for image processing in a distributed computational environment for an unmanned aerial vehicle. International Journal of Pattern Recognition and Artificial Intelligence, 20(5):763–780. DOI: 10.1142/S0218001406004867. A runtime system for implementation of image processing operations is presented. It is designed for working in a flexible and distributed environment related to the software architecture of a newly developed UAV system. The software architecture can be characterized at a coarse scale as a layered system, with a deliberative layer at the top, a reactive layer in the middle, and a processing layer at the bottom. At a finer scale each of the three levels is decomposed into sets of modules which communicate using CORBA, allowing system development and deployment on the UAV to be made in a highly flexible way. Image processing takes place in a dedicated module located in the process layer, and is the main focus of the paper. This module has been designed as a runtime system for data flow graphs, allowing various processing operations to be created online and on demand by the higher levels of the system. The runtime system is implemented in Java, which allows development and deployment to be made on a wide range of hardware/software configurations. Optimizations for particular hardware platforms have been made using Java's native interface. 
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[19] 
2006. Probabilistic roadmap based path planning for an autonomous unmanned helicopter. Journal of Intelligent & Fuzzy Systems, 17(4):395–405. IOS Press. 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. For both military and civil applications, there is a desire to develop more sophisticated UAV platforms where the emphasis is placed on development of intelligent capabilities. Imagine a mission scenario where a UAV is supplied with a 3D model of a region containing buildings and road structures and is instructed to fly to an arbitrary number of building structures and collect video streams of each of the building's respective facades. In this article, we describe a fully operational UAV platform which can achieve such missions autonomously. We focus on the path planner integrated with the platform which can generate collision free paths autonomously during such missions. Both probabilistic roadmapbased (PRM) and rapidly exploring random treesbased (RRT) algorithms have been used with the platform. The PRMbased path planner has been tested together with the UAV platform in an urban environment used for UAV experimentation. 
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[18] 
2006. A knowledge processing middleware framework and its relation to the JDL data fusion model. Journal of Intelligent & Fuzzy Systems, 17(4):335–351. IOS Press. Any autonomous system embedded in a dynamic and changing environment must be able to create qualitative knowledge and object structures representing aspects of its environment on the fly from raw or preprocessed sensor data in order to reason qualitatively about the environment and to supply such state information to other nodes in the distributed network in which it is embedded. These structures must be managed and made accessible to deliberative and reactive functionalities whose successful operation is dependent on being situationally aware of the changes in both the robotic agent's embedding and internal environments. DyKnow is a knowledge processing middleware framework which provides a set of functionalities for contextually creating, storing, accessing and processing such structures. The framework is implemented and has been deployed as part of a deliberative/reactive architecture for an autonomous unmanned aerial vehicle. The architecture itself is distributed and uses realtime CORBA as a communications infrastructure. We describe the system and show how it can be used to create more abstract entity and state representations of the world which can then be used for situation awareness by an unmanned aerial vehicle in achieving mission goals. We also show that the framework is a working instantiation of many aspects of the JDL data fusion model. 
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[17] 
2006. Approximate Databases: A support tool for approximate reasoning. Journal of applied nonclassical logics, 16(12):87–118. Ã‰ditions HermÃ¨sLavoisier. DOI: 10.3166/jancl.16.87117. Note: Special issue on implementation of logics 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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2004  
[16] 
2004. DyKnow: An approach to middleware for knowledge processing. Journal of Intelligent & Fuzzy Systems, 15(1):3–13. IOS Press. Any autonomous system embedded in a dynamic and changing environment must be able to create qualitative knowledge and object structures representing aspects of its environment on the fly from raw or preprocessed sensor data in order to reason qualitatively about the environment. These structures must be managed and made accessible to deliberative and reactive functionalities which are dependent on being situationally aware of the changes in both the robotic agent's embedding and internal environment. DyKnow is a software framework which provides a set of functionalities for contextually accessing, storing, creating and processing such structures. The system is implemented and has been deployed in a deliberative/reactive architecture for an autonomous unmanned aerial vehicle. The architecture itself is distributed and uses realtime CORBA as a communications infrastructure. We describe the system and show how it can be used in execution monitoring and chronicle recognition scenarios for UAV applications. 
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[15] 
2004. Issues in Designing Physical Agents for Dynamic RealTime Environments: World Modeling, Planning, Learning, and Communicating. The AI Magazine, 25(2):137–138. AAAI Press. This article discusses a workshop held in conjunction with the Eighteenth International Joint Conference on Artificial Intelligence (IJCAI03), held in Acapulco, Mexico, on 11 August 2003. 
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2003  
[14] 
2003. Towards a framework for approximate ontologies. Fundamenta Informaticae, 57(24):147–165. IOS Press. Currently, there is a great deal of interest in developing tools for the generation and use of ontologies on the WWW. These knowledge structures are considered essential to the success of the semantic web, the next phase in the evolution of the WWW. Much recent work with ontologies assumes that the concepts used as building blocks are crisp as opposed to approximate. It is a premise of this paper that approximate concepts and ontologies will become increasingly more important as the semantic web becomes a reality. We propose a framework for specifying, generating and using approximate ontologies. More specifically, (1) a formal framework for defining approximate concepts, ontologies and operations on approximate concepts and ontologies is presented. The framework is based on intuitions from rough set theory, (2) algorithms for automatically generating approximate ontologies from traditional crisp ontologies or from large data sets together with additional knowledge are presented. The knowledge will generally be related to similarity measurements between individual objects in the data sets, or constraints of a logical nature which rule out particular constellations of concepts and dependencies in generated ontologies. The techniques for generating approximate ontologies are parameterizable. The paper provides specific instantiations and examples. 
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[13] 
2003. 2003 AAAI Spring Symposium Series. The AI Magazine, 24(3):131–140. AAAI Press. The American Association for Artificial Intelligence, in cooperation with Stanford Universityâ€™s Department of Computer Science, presented the 2003 Spring Symposium Series, Monday through Wednesday, 24â€“26 March 2003, at Stanford University. The titles of the eight symposia were AgentMediated 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 QuestionAnswering Motivation. 
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2001  
[12] 
2001. TALPLANNER  A temporal logicbased planner. The AI Magazine, 22(3):95–102. AAAI Press. TALPLANNER is a forwardchaining planner that utilizes domaindependent knowledge to control search in the state space generated by action invocation. The domaindependent control knowledge, background knowledge, plans, and goals are all represented, using,formulas in, a temporal logic called TAL, which has been developed independently as a formalism for specifying agent narratives and reasoning about them. In the Fifth International Artificial Intelligence Planning and Scheduling Conference planning competition, TALPLANNER exhibited impressive performance, winning the Outstanding Performance Award in the DomainDependent Planning Competition. In this article, we provide an overview of TALPLANNER. 
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2000  
[11] 
2000. TALplanner: A temporal logic based forward chaining planner. Annals of Mathematics and Artificial Intelligence, 30(14):119–169. Springer. DOI: 10.1023/A:1016619613658. We present TALplanner, a forwardchaining planner based on the use of domaindependent search control knowledge represented as formulas in the Temporal Action Logic (TAL). TAL is a narrative based linear metric time logic used for reasoning about action and change in incompletely specified dynamic environments. TAL is used as the formal semantic basis for TALplanner, where a TAL goal narrative with control formulas is input to TALplanner which then generates a TAL narrative that entails the goal and control formulas. The sequential version of TALplanner is presented. The expressivity of plan operators is then extended to deal with an interesting class of resource types. An algorithm for generating concurrent plans, where operators have varying durations and internal state, is also presented. All versions of TALplanner have been implemented. The potential of these techniques is demonstrated by applying TALplanner to a number of standard planning benchmarks in the literature. 
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[10] 
2000. The PMA and relativizing minimal change for action update. Fundamenta Informaticae, 44(12):95–131. IOS Press. Recently, a great deal of progress has been made using nonmonotonic temporal logics to formalize reasoning about action and change. In particular, much focus has been placed on the proper representation of nondeterministic actions and the indirect effects of actions. For the latter the use of causal or fluent dependency rule approaches has been dominant. Although much recent effort has also been spent applying the belief revision/update (BR/U) approach to the action and change domain, there has been less progress in dealing with nondeterministic update and indirect effects represented as integrity constraints. We demonstrate that much is to be gained by crossfertilization between the two paradigms and we show this in the following manner. We first propose a generalization of the PMA, called the modified MPMA which uses intuitions from the TL paradigm to permit representation of nondeterministic update and the use of integrity constraints interpreted as causal or fluent dependency rules. We provide several syntactic characterizations of MPMA, one of which is in terms of a simple temporal logic and provide a representation theorem showing equivalence between the two. In constructing the MPMA, we discovered a syntactic anomaly which we call the redundant atom anomaly that many TL approaches suffer from. We provide a method for avoiding the problem which is equally applicable across paradigms. We also describe a syntactic characterization of MPMA in terms of Dijkstra semantics. We set up a framework for future generalization of the BR/U approach and conclude with a formal comparison of related approaches. 
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[9] 
2000. Tackling the qualification problem using fluent dependency constraints. In the area of formal reasoning about action and change, one of the fundamental representation problems is providing concise modular and incremental specifications of action types and world models, where instantiations of action types are invoked by agents such as mobile robots. Provided the preconditions to the action are true, their invocation results in changes to the world model concomitant with the goaldirected behavior of the agent. One particularly difficult class of related problems, collectively called the qualification problem, deals with the need to find a concise incremental and modular means of characterizing the plethora of exceptional conditions that might qualify an action, but generally do not, without having to explicitly enumerate them in the preconditions to an action. We show how fluent dependency constraints together with the use of durational fluents can be used to deal with problems associated with action qualification using a temporal logic for action and change called TALQ. We demonstrate the approach using action scenarios that combine solutions to the frame, ramification, and qualification problems in the context of actions with duration, concurrent actions, nondeterministic actions, and the use of both Boolean and nonBoolean fluents. The circumscription policy used for the combined problems is reducible to the firstorder case. 
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1999  
[8] 
1999. Metaqueries on deductive databases. We introduce the notion of a metaquery on relational databases and a technique which can be used to represent and solve a number of interesting problems from the area of knowledge representation using logic. The technique is based on the use of quantifier elimination and may also be used to query relational databases using a declarative query language called SHQL (SemiHorn Query Language), introduced in [6]. SHQL is a fragment of classical firstorder predicate logic and allows us to define a query without supplying its explicit definition. All SHQL queries to the database can be processed in polynomial time (both on the size of the input query and the size of the database). We demonstrate the use of the technique in problem solving by structuring logical puzzles from the Knights and Knaves domain as SHQL metaqueries on relational databases. We also provide additional examples demonstrating the flexibility of the technique. We conclude with a description of a newly developed software tool, The Logic Engineer, which aids in the description of algorithms using transformation and reduction techniques such as those applied in the metaquerying approach. 
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[7] 
1999. Declarative PTIME queries for relational databases using quantifier elimination. Journal of logic and computation (Print), 9(5):737–758. Oxford University Press. DOI: 10.1093/logcom/9.5.737. In this paper, we consider the problem of expressing and computing queries on relational deductive databases in a purely declarative query language, called SHQL (SemiHorn 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 firstorder theory not limited by the rulebased 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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1998  
[6] 
1998. (TAL) temporal action logics: Language specification and tutorial. Electronic Transactions on Artifical Intelligence, 2(34):273–306. Link: http://www.ep.liu.se/ej/etai/1998/009/ The purpose of this article is to provide a uniform, lightweight language specication and tutorial for a class of temporal logics for reasoning about action and change that has been developed by our group during the period 19941998. The class of logics are collected under the name TAL, an acronym for Temporal Action Logics. TAL has its origins and inspiration in the work with Features and Fluents (FF) by Sandewall, but has diverged from the methodology and approach through the years. We first discuss distinctions and compatibility with FF, move on to the lightweight language specication, and then present a tutorial in terms of an excursion through the different parts of a relatively complex narrative defined using TAL. We conclude with an annotated list of published work from our group. The article tries to strike a reasonable balance between detail and readability, making a number of simplications regarding narrative syntax and translation to a base logical language. Full details are available in numerous technical reports and articles which are listed in the final section of this article. 
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[5] 
1998. General domain circumscription and its effective reductions. We first define general domain circumscription (GDC) and provide it with a semantics. GDC subsumes existing domain circumscription proposals in that it allows varying of arbitrary predicates, functions, or constants, to maximize the minimization of the domain of a theory. We then show that for the class of semiuniversal theories without function symbols, that the domain circumscription of such theories can be constructively reduced to logically equivalent firstorder theories by using an extension of the DLS algorithm, previously proposed by the authors for reducing secondorder formulas. We also show that for a certain class of domain circumscribed theories, that any arbitrary secondorder circumscription policy applied to these theories is guaranteed to be reducible to a logically equivalent firstorder theory. In the case of semiuniversal theories with functions and arbitrary theories which are not separated, we provide additional results, which although not guaranteed to provide reductions in all cases, do provide reductions in some cases. These results are based on the use of fixpoint reductions. 
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1997  
[4] 
1997. Computing circumscription revisited: A reduction algorithm. Journal of automated reasoning, 18(3):297–336. Kluwer Academic Publishers. DOI: 10.1023/A:1005722130532. 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 secondorder 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, secondorder formulas into equivalent firstorder 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 firstorder formulas. The algorithm takes as input an arbitrary secondorder formula and either returns as output an equivalent firstorder formula, or terminates with failure. The class of secondorder 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 nary 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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1996  
[3] 
1996. A reduction result for circumscribed semihorn formulas. 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 secondorder formulas. One proposal for dealing with the computational problems is to identify classes of firstorder formulas whose circumscription can be shown to be equivalent to a firstorder formula. In previous work, we presented an algorithm which reduces certain classes of secondorder circumscription axioms to logically equivalent firstorder 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 <em>semiHorn formulas</em>. Our results subsume previous results by Kolaitis and Papadimitriou regarding a characterization of circumscribed definite logic programs which are firstorder 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 semiHorn 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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1993  
[2] 
1993. Fuzzy ifthenunless rules and their implementation. International Journal of Uncertainty Fuzziness and KnowledgeBased Systems, 1(2):167–182. World Scientific. DOI: 10.1142/S0218488593000097. We consider the possibility of generalizing the notion of a fuzzy IfThen rule to take into account its context dependent nature. We interpret fuzzy rules as modeling a forward directed causal relationship between the antecedent and the conclusion, which applies in most contexts, but on occasion breaks down in exceptional contexts. The default nature of the rule is modeled by augmenting the original IfThen rule with an exception part. We then consider the proper semantic correlate to such an addition and propose a ternary relation which satisfies a number of intuitive constraints described in terms of a number of inference rules. In the rest of the paper, we consider implementational issues arising from the unless extension and propose the use of reason maintenance systems, in particular TMS's, where a fuzzy IfThenUnless rule is encoded into a dependency net. We verify that the net satisfies the constraints stated in the inference schemes and conclude with a discussion concerning the integration of qualitative INOUT labelings of the TMS with quantitative degree of membership labelings for the variables in question. 
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1992  
[1] 
1992. NML3  A nonmonotonic logic with explicit defaults. Journal of applied nonclassical logics, 2(1):9–48. Ã‰ditions HermÃ¨sLavoisier. 
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