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2014
[33] Per-Magnus Olsson. 2014.
Methods for Network Optimization and Parallel Derivative-free Optimization.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #1580. Link√∂ping University Electronic Press. 319 pages. ISBN: 978-91-7519-388-5 (print).
DOI: 10.3384/diss.diva-104110.

This thesis is divided into two parts that each is concerned with a specific problem.The problem under consideration in the first part is to find suitable graph representations, abstractions, cost measures and algorithms for calculating placements of unmanned aerial vehicles (UAVs) such that they can keep one or several static targets under constant surveillance. Each target is kept under surveillance by a surveillance UAV, which transmits information, typically real time video, to a relay UAV. The role of the relay UAV is to retransmit the information to another relay UAV, which retransmits it again to yet another UAV. This chain of retransmission continues until the information eventually reaches an operator at a base station.When there is a single target, then all Pareto-optimal solutions, i.e. all relevant compromises between quality and the number of UAVs required, can be found using an efficient new algorithm. If there are several targets, the problem becomes a variant of the Steiner tree problem and to solve this problem we adapt an existing algorithm to find an initial tree. Once it is found, we can further improve it using a new algorithm presentedin this thesis.The second problem is optimization of time-consuming problems where the objective function is seen as a black box, where the input parameters are sent and a function valueis returned. This has the important implication that no gradient or Hessian information is available. Such problems are common when simulators are used to perform advanced calculations such as crash test simulations of cars, dynamic multibody simulations etc. It is common that a single function evaluation takes several hours.Algorithms for solving such problems can be broadly divided into direct search algorithms and model building algorithms. The first kind evaluates the objective function directly, whereas the second kind builds a model of the objective function, which is then optimized in order to find a new point where it is believed that objective function has agood value. Then the objective function is evaluated in that point.Since the objective function is very time-consuming, it is common to focus on minimizing the number of function evaluations. However, this completely disregards the possibility to perform calculations in parallel and to exploit this we investigate different ways parallelization can be used in model-building algorithms. Some of the ways to do this is to use several starting points, generate several new points in each iteration, new ways of predicting a point’s value and more.We have implemented the parallel extensions in one of the state of the art algorithms for derivative-free optimization and report results from testing on synthetic benchmarksas well as from solving real industrial problems.

2011
[32] Full text  Piotr Rudol. 2011.
Increasing Autonomy of Unmanned Aircraft Systems Through the Use of Imaging Sensors.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1510. Link√∂ping University Electronic Press. 96 pages. ISBN: 978-91-7393-034-5.

The range of missions performed by Unmanned Aircraft Systems (UAS) has been steadily growing in the past decades thanks to continued development in several disciplines. The goal of increasing the autonomy of UAS's is widening the range of tasks which can be carried out without, or with minimal, external help. This thesis presents methods for increasing specific aspects of autonomy of UAS's operating both in outdoor and indoor environments where cameras are used as the primary sensors.First, a method for fusing color and thermal images for object detection, geolocation and tracking for UAS's operating primarily outdoors is presented. Specifically, a method for building saliency maps where human body locations are marked as points of interest is described. Such maps can be used in emergency situations to increase the situational awareness of first responders or a robotic system itself. Additionally, the same method is applied to the problem of vehicle tracking. A generated stream of geographical locations of tracked vehicles increases situational awareness by allowing for qualitative reasoning about, for example, vehicles overtaking, entering or leaving crossings.Second, two approaches to the UAS indoor localization problem in the absence of GPS-based positioning are presented. Both use cameras as the main sensors and enable autonomous indoor ight and navigation. The first approach takes advantage of cooperation with a ground robot to provide a UAS with its localization information. The second approach uses marker-based visual pose estimation where all computations are done onboard a small-scale aircraft which additionally increases its autonomy by not relying on external computational power.

[31] Full text  Mariusz Wzorek. 2011.
Selected Aspects of Navigation and Path Planning in Unmanned Aircraft Systems.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1509. Link√∂ping University Electronic Press. 107 pages. ISBN: 978-91-7393-037-6.

Unmanned aircraft systems (UASs) are an important future technology with early generations already being used in many areas of application encompassing both military and civilian domains. This thesis proposes a number of integration techniques for combining control-based navigation with more abstract path planning functionality for UASs. These techniques are empirically tested and validated using an RMAX helicopter platform used in the UASTechLab at Linköping University. Although the thesis focuses on helicopter platforms, the techniques are generic in nature and can be used in other robotic systems.At the control level a navigation task is executed by a set of control modes. A framework based on the abstraction of hierarchical concurrent state machines for the design and development of hybrid control systems is presented. The framework is used to specify reactive behaviors and for sequentialisation of control modes. Selected examples of control systems deployed on UASs are presented. Collision-free paths executed at the control level are generated by path planning algorithms.We propose a path replanning framework extending the existing path planners to allow dynamic repair of flight paths when new obstacles or no-fly zones obstructing the current flight path are detected. Additionally, a novel approach to selecting the best path repair strategy based on machine learning technique is presented. A prerequisite for a safe navigation in a real-world environment is an accurate geometrical model. As a step towards building accurate 3D models onboard UASs initial work on the integration of a laser range finder with a helicopter platform is also presented.Combination of the techniques presented provides another step towards building comprehensive and robust navigation systems for future UASs.

[30] Full text  David Land√©n. 2011.
Complex Task Allocation for Delegation: From Theory to Practice.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1506. Link√∂ping University Electronic Press. 139 pages. ISBN: 978-91-7393-048-2.

The problem of determining who should do what given a set of tasks and a set of agents is called the task allocation problem. The problem occurs in many multi-agent system applications where a workload of tasks should be shared by a number of agents. In our case, the task allocation problem occurs as an integral part of a larger problem of determining if a task can be delegated from one agent to another.Delegation is the act of handing over the responsibility for something to someone. Previously, a theory for delegation including a delegation speech act has been specified. The speech act specifies the preconditions that must be fulfilled before the delegation can be carried out, and the postconditions that will be true afterward. To actually use the speech act in a multi-agent system, there must be a practical way of determining if the preconditions are true. This can be done by a process that includes solving a complex task allocation problem by the agents involved in the delegation.In this thesis a constraint-based task specification formalism, a complex task allocation algorithm for allocating tasks to unmanned aerial vehicles and a generic collaborative system shell for robotic systems are developed. The three components are used as the basis for a collaborative unmanned aircraft system that uses delegation for distributing and coordinating the agents' execution of complex tasks.

[29] Full text  H√•kan Warnquist. 2011.
Computer-Assisted Troubleshooting for Efficient Off-board Diagnosis.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1490. Link√∂ping University Electronic Press. 169 pages. ISBN: 978-91-7393-151-9.

This licentiate thesis considers computer-assisted troubleshooting of complex products such as heavy trucks. The troubleshooting task is to find and repair all faulty components in a malfunctioning system. This is done by performing actions to gather more information regarding which faults there can be or to repair components that are suspected to be faulty. The expected cost of the performed actions should be as low as possible.The work described in this thesis contributes to solving the troubleshooting task in such a way that a good trade-off between computation time and solution quality can be made. A framework for troubleshooting is developed where the system is diagnosed using non-stationary dynamic Bayesian networks and the decisions of which actions to perform are made using a new planning algorithm for Stochastic Shortest Path Problems called Iterative Bounding LAO*.It is shown how the troubleshooting problem can be converted into a Stochastic Shortest Path problem so that it can be efficiently solved using general algorithms such as Iterative Bounding LAO*. New and improved search heuristics for solving the troubleshooting problem by searching are also presented in this thesis.The methods presented in this thesis are evaluated in a case study of an auxiliary hydraulic braking system of a modern truck. The evaluation shows that the new algorithm Iterative Bounding LAO* creates troubleshooting plans with a lower expected cost faster than existing state-of-the-art algorithms in the literature. The case study shows that the troubleshooting framework can be applied to systems from the heavy vehicles domain.

[28] Full text  Per-Magnus Olsson. 2011.
Positioning Algorithms for Surveillance Using Unmanned Aerial Vehicles.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1476. Link√∂ping University Electronic Press. 140 pages. ISBN: 978-91-7393-200-4.

Surveillance is an important application for unmanned aerial vehicles (UAVs). The sensed information often has high priority and it must be made available to human operators as quickly as possible. Due to obstacles and limited communication range, it is not always possible to transmit the information directly to the base station. In this case, other UAVs can form a relay chain between the surveillance UAV and the base station. Determining suitable positions for such UAVs is a complex optimization problem in and of itself, and is made even more diÔ¨Écult by communication and surveillance constraints.To solve diÔ¨Äerent variations of Ô¨Ānding positions for UAVs for surveillance of one target, two new algorithms have been developed. One of the algorithms is developed especially for Ô¨Ānding a set of relay chains oÔ¨Äering diÔ¨Äerent trade-oÔ¨Äs between the number of UAVsand the quality of the chain. The other algorithm is tailored towards Ô¨Ānding the highest quality chain possible, given a limited number of available UAVs.Finding the optimal positions for surveillance of several targets is more diÔ¨Écult. A study has been performed, in order to determine how the problems of interest can besolved. It turns out that very few of the existing algorithms can be used due to the characteristics of our speciÔ¨Āc problem. For this reason, an algorithm for quickly calculating positions for surveillance of multiple targets has been developed. This enables calculation of an initial chain that is immediately made available to the user, and the chain is then incrementally optimized according to the user‚Äôs desire.

2009
[27] Full text  Cyrille Berger. 2009.
Perception de la géométrie de l'environment pour la navigation autonome.
PhD Thesis. Universit√© de Toulouse. 164 pages.

Le but de la recherche en robotique mobile est de donner aux robots la capacité d'accomplir des missions dans un environnement qui n'est pas parfaitement connu. Mission, qui consiste en l'exécution d'un certain nombre d'actions élémentaires (déplacement, manipulation d'objets...) et qui nécessite une localisation précise, ainsi que la construction d'un bon modèle géométrique de l'environnement, a partir de l'exploitation de ses propres capteurs, des capteurs externes, de l'information provenant d'autres robots et de modèle existant, par exemple d'un système d'information géographique. L'information commune est la géométrie de l'environnement. La première partie du manuscrit couvre les différentes méthodes d'extraction de l'information géométrique. La seconde partie présente la création d'un modèle géométrique en utilisant un graphe, ainsi qu'une méthode pour extraire de l'information du graphe et permettre au robot de se localiser dans l'environnement.

[26] Full text  Gianpaolo Conte. 2009.
Vision-Based Localization and Guidance for Unmanned Aerial Vehicles.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #1260. Link√∂ping University Electronic Press. 174 pages. ISBN: 978-91-7393-603-3.

The thesis has been developed as part of the requirements for a PhD degree at the Artificial Intelligence and Integrated Computer System division (AIICS) in the Department of Computer and Information Sciences at Linköping University.The work focuses on issues related to Unmanned Aerial Vehicle (UAV) navigation, in particular in the areas of guidance and vision-based autonomous flight in situations of short and long term GPS outage.The thesis is divided into two parts. The first part presents a helicopter simulator and a path following control mode developed and implemented on an experimental helicopter platform. The second part presents an approach to the problem of vision-based state estimation for autonomous aerial platforms which makes use of geo-referenced images for localization purposes. The problem of vision-based landing is also addressed with emphasis on fusion between inertial sensors and video camera using an artificial landing pad as reference pattern. In the last chapter, a solution to a vision-based ground object geo-location problem using a fixed-wing micro aerial vehicle platform is presented.The helicopter guidance and vision-based navigation methods developed in the thesis have been implemented and tested in real flight-tests using a Yamaha Rmax helicopter. Extensive experimental flight-test results are presented.

[25] Full text  Fredrik  Heintz. 2009.
DyKnow: A Stream-Based Knowledge Processing Middleware Framework.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #1240. Link√∂ping University Electronic Press. 258 pages. ISBN: 978‚Äď91‚Äď7393‚Äď696‚Äď5.

As robotic systems become more and more advanced the need to integrate existing deliberative functionalities such as chronicle recognition, motion planning, task planning, and execution monitoring increases. To integrate such functionalities into a coherent system it is necessary to reconcile the different formalisms used by the functionalities to represent information and knowledge about the world. To construct and integrate these representations and maintain a correlation between them and the environment it is necessary to extract information and knowledge from data collected by sensors. However, deliberative functionalities tend to assume symbolic and crisp knowledge about the current state of the world while the information extracted from sensors often is noisy and incomplete quantitative data on a much lower level of abstraction. There is a wide gap between the information about the world normally acquired through sensing and the information that is assumed to be available for reasoning about the world.As physical autonomous systems grow in scope and complexity, bridging the gap in an ad-hoc manner becomes impractical and inefficient. Instead a principled and systematic approach to closing the sensereasoning gap is needed. At the same time, a systematic solution has to be sufficiently flexible to accommodate a wide range of components with highly varying demands. We therefore introduce the concept of knowledge processing middleware for a principled and systematic software framework for bridging the gap between sensing and reasoning in a physical agent. A set of requirements that all such middleware should satisfy is also described.A stream-based knowledge processing middleware framework called DyKnow is then presented. Due to the need for incremental refinement of information at different levels of abstraction, computations and processes within the stream-based knowledge processing framework are modeled as active and sustained knowledge processes working on and producing streams. DyKnow supports the generation of partial and context dependent stream-based representations of past, current, and potential future states at many levels of abstraction in a timely manner.To show the versatility and utility of DyKnow two symbolic reasoning engines are integrated into Dy-Know. The first reasoning engine is a metric temporal logical progression engine. Its integration is made possible by extending DyKnow with a state generation mechanism to generate state sequences over which temporal logical formulas can be progressed. The second reasoning engine is a chronicle recognition engine for recognizing complex events such as traffic situations. The integration is facilitated by extending DyKnow with support for anchoring symbolic object identifiers to sensor data in order to collect information about physical objects using the available sensors. By integrating these reasoning engines into DyKnow, they can be used by any knowledge processing application. Each integration therefore extends the capability of DyKnow and increases its applicability.To show that DyKnow also has a potential for multi-agent knowledge processing, an extension is presented which allows agents to federate parts of their local DyKnow instances to share information and knowledge.Finally, it is shown how DyKnow provides support for the functionalities on the different levels in the JDL Data Fusion Model, which is the de facto standard functional model for fusion applications. The focus is not on individual fusion techniques, but rather on an infrastructure that permits the use of many different fusion techniques in a unified framework.The main conclusion of this thesis is that the DyKnow knowledge processing middleware framework provides appropriate support for bridging the sense-reasoning gap in a physical agent. This conclusion is drawn from the fact that DyKnow has successfully been used to integrate different reasoning engines into complex unmanned aerial vehicle (UAV) applications and that it satisfies all the stated requirements for knowledge processing middleware to a significant degree.

2008
[24] Full text  Per Nyblom. 2008.
Dynamic Abstraction for Interleaved Task Planning and Execution.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1363. Institutionen f√∂r datavetenskap. 94 pages. ISBN: 978-91-7393-905-8.
Note: Report code: LiU-Tek-Lic-2008:21.

It is often beneficial for an autonomous agent that operates in a complex environment to make use of different types of mathematical models to keep track of unobservable parts of the world or to perform prediction, planning and other types of reasoning. Since a model is always a simplification of something else, there always exists a tradeoff between the model’s accuracy and feasibility when it is used within a certain application due to the limited available computational resources. Currently, this tradeoff is to a large extent balanced by humans for model construction in general and for autonomous agents in particular. This thesis investigates different solutions where such agents are more responsible for balancing the tradeoff for models themselves in the context of interleaved task planning and plan execution. The necessary components for an autonomous agent that performs its abstractions and constructs planning models dynamically during task planning and execution are investigated and a method called DARE is developed that is a template for handling the possible situations that can occur such as the rise of unsuitable abstractions and need for dynamic construction of abstraction levels. Implementations of DARE are presented in two case studies where both a fully and partially observable stochastic domain are used, motivated by research with Unmanned Aircraft Systems. The case studies also demonstrate possible ways to perform dynamic abstraction and problem model construction in practice.

[23] Full text  Heike Joe Steinhauer. 2008.
A Representation Scheme for Description and Reconstruction of Object Configurations Based on Qualitative Relations.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #1204. Link√∂ping University Electronic Press. 178 pages. ISBN: 978-91-7393-823-5.

One reason Qualitative Spatial Reasoning (QSR) is becoming increasingly important to Artificial Intelligence (AI) is the need for a smooth ‚Äėhuman-like‚Äô communication between autonomous agents and people. The selected, yet general, task motivating the work presented here is the scenario of an object configuration that has to be described by an observer on the ground using only relational object positions. The description provided should enable a second agent to create a map-like picture of the described configuration in order to recognize the configuration on a representation from the survey perspective, for instance on a geographic map or in the landscape itself while observing it from an aerial vehicle. Either agent might be an autonomous system or a person. Therefore, the particular focus of this work lies on the necessity to develop description and reconstruction methods that are cognitively easy to apply for a person.This thesis presents the representation scheme QuaDRO (Qualitative Description and Reconstruction of Object configurations). Its main contributions are a specification and qualitative classification of information available from different local viewpoints into nine qualitative equivalence classes. This classification allows the preservation of information needed for reconstruction nto a global frame of reference. The reconstruction takes place in an underlying qualitative grid with adjustable granularity. A novel approach for representing objects of eight different orientations by two different frames of reference is used. A substantial contribution to alleviate the reconstruction process is that new objects can be inserted anywhere within the reconstruction without the need for backtracking or rereconstructing. In addition, an approach to reconstruct configurations from underspecified descriptions using conceptual neighbourhood-based reasoning and coarse object relations is presented.

2007
[22] Bj√∂rn H√§gglund. 2007.
A framework for designing constraint stores.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1302. Link√∂pings universitet. 118 pages. ISBN: 978-91-85715-70-1.

A constraint solver based on concurrent search and propagation provides a well-defined component model for propagators by enforcing a strict two-level architecture. This makes it straightforward for third parties to invent, implement and deploy new kinds of propagators. The most critical components of such solvers are the constraint stores through which propagators communicate with each other. Introducing stores supporting new kinds of stored constraints can potentially increase the solving power by several orders of magnitude. This thesis presents a theoretical framework for designing stores achieving this without loss of propagator interoperability.

[21] Full text  Gianpaolo Conte. 2007.
Navigation Functionalities for an Autonomous UAV Helicopter.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1307. Link√∂ping University Electronic Press. 74 pages. ISBN: 978-91-85715-35-0.

This thesis was written during the WITAS UAV Project where one of the goals has been the development of a software/hardware architecture for an unmanned autonomous helicopter, in addition to autonomous functionalities required for complex mission scenarios. The algorithms developed here have been tested on an unmanned helicopter platform developed by Yamaha Motor Company called the RMAX. The character of the thesis is primarily experimental and it should be viewed as developing navigational functionality to support autonomous flight during complex real world mission scenarios. This task is multidisciplinary since it requires competence in aeronautics, computer science and electronics. The focus of the thesis has been on the development of a control method to enable the helicopter to follow 3D paths. Additionally, a helicopter simulation tool has been developed in order to test the control system before flight-tests. The thesis also presents an implementation and experimental evaluation of a sensor fusion technique based on a Kalman filter applied to a vision based autonomous landing problem. Extensive experimental flight-test results are presented.

[20] Full text  Martin Magnusson. 2007.
Deductive Planning and Composite Actions in Temporal Action Logic.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1329. Institutionen f√∂r datavetenskap. 85 pages. ISBN: 978-91-85895-93-9.

Temporal Action Logic is a well established logical formalism for reasoning about action and change that has long been used as a formal specification language. Its first-order characterization and explicit time representation makes it a suitable target for automated theorem proving and the application of temporal constraint solvers. We introduce a translation from a subset of Temporal Action Logic to constraint logic programs that takes advantage of these characteristics to make the logic applicable, not just as a formal specification language, but in solving practical reasoning problems. Extensions are introduced that enable the generation of action sequences, thus paving the road for interesting applications in deductive planning. The use of qualitative temporal constraints makes it possible to follow a least commitment strategy and construct partially ordered plans. Furthermore, the logical language and logic program translation is extended with the notion of composite actions that can be used to formulate and execute scripted plans with conditional actions, non-deterministic choices, and loops. The resulting planner and reasoner is integrated with a graphical user interface in our autonomous helicopter research system and applied to logistics problems. Solution plans are synthesized together with monitoring constraints that trigger the generation of recovery actions in cases of execution failures.

2006
[19] Full text  Karolina Eliasson. 2006.
The Use of Case-Based Reasoning in a Human-Robot Dialog System.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1248. Institutionen f√∂r datavetenskap. 130 pages. ISBN: 91-85523-78-X.
Note: Report code: LiU{Tek{Lic{2006:29.

As long as there have been computers, one goal has been to be able to communicate with them using natural language. It has turned out to be very hard to implement a dialog system that performs as well as a human being in an unrestricted domain, hence most dialog systems today work in small, restricted domains where the permitted dialog is fully controlled by the system.In this thesis we present two dialog systems for communicating with an autonomous agent:The first system, the WITAS RDE, focuses on constructing a simple and failsafe dialog system including a graphical user interface with multimodality features, a dialog manager, a simulator, and development infrastructures that provides the services that are needed for the development, demonstration, and validation of the dialog system. The system has been tested during an actual flight connected to an unmanned aerial vehicle.The second system, CEDERIC, is a successor of the dialog manager in the WITAS RDE. It is equipped with a built-in machine learning algorithm to be able to learn new phrases and dialogs over time using past experiences, hence the dialog is not necessarily fully controlled by the system. It also includes a discourse model to be able to keep track of the dialog history and topics, to resolve references and maintain subdialogs. CEDERIC has been evaluated through simulation tests and user tests with good results.

[18] Full text  Patrik Haslum. 2006.
Admissible Heuristics for Automated Planning.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #1004. Institutionen f√∂r datavetenskap. 164 pages. ISBN: 91-85497-28-2.
Link to Licentiate Thesis: http://urn.kb.se/resolve?urn=urn:nbn:se:...

The problem of domain-independent automated planning has been a topic of research in Artificial Intelligence since the very beginnings of the field. Due to the desire not to rely on vast quantities of problem specific knowledge, the most widely adopted approach to automated planning is search. The topic of this thesis is the development of methods for achieving effective search control for domain-independent optimal planning through the construction of admissible heuristics. The particular planning problem considered is the so called ‚Äúclassical‚ÄĚ AI planning problem, which makes several restricting assumptions. Optimality with respect to two measures of plan cost are considered: in planning with additive cost, the cost of a plan is the sum of the costs of the actions that make up the plan, which are assumed independent, while in planning with time, the cost of a plan is the total execution time ‚Äď makespan ‚Äď of the plan. The makespan optimization objective can not, in general, be formulated as a sum of independent action costs and therefore necessitates a problem model slightly different from the classical one. A further small extension to the classical model is made with the introduction of two forms of capacitated resources. Heuristics are developed mainly for regression planning, but based on principles general enough that heuristics for other planning search spaces can be derived on the same basis. The thesis describes a collection of methods, including the h<sup>m</sup>, additive h<sup>m</sup> and improved pattern database heuristics, and the relaxed search and boosting techniques for improving heuristics through limited search, and presents two extended experimental analyses of the developed methods, one comparing heuristics for planning with additive cost and the other concerning the relaxed search technique in the context of planning with time, aimed at discovering the characteristics of problem domains that determine the relative effectiveness of the compared methods. Results indicate that some plausible such characteristics have been found, but are not entirely conclusive.

[17] Full text  Per Olof Pettersson. 2006.
Sampling-based Path Planning for an Autonomous Helicopter.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1229. Institutionen f√∂r datavetenskap. 141 pages. ISBN: 91‚Äď85497‚Äď15‚Äď0.
Note: Report code: LiU‚ÄďTek‚ÄďLic‚Äď2006:10.

Many of the applications that have been proposed for future small unmanned aerial vehicles (UAVs) are at low altitude in areas with many obstacles. A vital component for successful navigation in such environments is a path planner that can find collision free paths for the UAV.Two popular path planning algorithms are the probabilistic roadmap algorithm (PRM) and the rapidly-exploring random tree algorithm (RRT).Adaptations of these algorithms to an unmanned autonomous helicopter are presented in this thesis, together with a number of extensions for handling constraints at different stages of the planning process.The result of this work is twofold:First, the described planners and extensions have been implemented and integrated into the software architecture of a UAV. A number of flight tests with these algorithms have been performed on a physical helicopter and the results from some of them are presented in this thesis.Second, an empirical study has been conducted, comparing the performance of the different algorithms and extensions in this planning domain. It is shown that with the environment known in advance, the PRM algorithm generally performs better than the RRT algorithm due to its precompiled roadmaps, but that the latter is also usable as long as the environment is not too complex. The study also shows that simple geometric constraints can be added in the runtime phase of the PRM algorithm, without a big impact on performance. It is also shown that postponing the motion constraints to the runtime phase can improve the performance of the planner in some cases.

2005
[16] Anders Arpteg. 2005.
Intelligent semi-structured information extraction: a user-driven approach to information extraction.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #946. Link√∂ping University Electronic Press. 139 pages. ISBN: 91-85297-98-4.
Note: This work has been supported by University of Kalmar and the Knowledge Foundation.

The number of domains and tasks where information extraction tools can be used needs to be increased. One way to reach this goal is to design user-driven information extraction systems where non-expert users are able to adapt them to new domains and tasks. It is difficult to design general extraction systems that do not require expert skills or a large amount of work from the user. Therefore, it is difficult to increase the number of domains and tasks. A possible alternative is to design user-driven systems, which solve that problem by letting a large number of non-expert users adapt the systems themselves. To accomplish this goal, the systems need to become more intelligent and able to learn to extract with as little given information as possible.The type of information extraction system that is in focus for this thesis is semi-structured information extraction. The term semi-structured refers to documents that not only contain natural language text but also additional structural information. The typical application is information extraction from World Wide Web hypertext documents. By making effective use of not only the link structure but also the structural information within each such document, user-driven extraction systems with high performance can be built.There are two different approaches presented in this thesis to solve the user-driven extraction problem. The first takes a machine learning approach and tries to solve the problem using a modified $Q(\lambda)$ reinforcement learning algorithm. A problem with the first approach was that it was difficult to handle extraction from the hidden Web. Since the hidden Web is about 500 times larger than the visible Web, it would be very useful to be able to extract information from that part of the Web as well. The second approach is called the hidden observation approach and tries to also solve the problem of extracting from the hidden Web. The goal is to have a user-driven information extraction system that is also able to handle the hidden Web. The second approach uses a large part of the system developed for the first approach, but the additional information that is silently obtained from the user presents other problems and possibilities.An agent-oriented system was designed to evaluate the approaches presented in this thesis. A set of experiments was conducted and the results indicate that a user-driven information extraction system is possible and no longer just a concept. However, additional work and research is necessary before a fully-fledged user-driven system can be designed.

[15] Bourhane Kadmiry. 2005.
Fuzzy gain scheduled visual servoing for an unmanned helicopter.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #938. Link√∂pings universitet. 148 pages. ISBN: 91-85297-76-3.

The overall objective of the Wallenberg Laboratory for Information Technology and Autonomous Systems (WITAS) at Linkoping University is the development of an intelligent command and control system, containing active-vision sensors, which supports the operation of an unmanned air vehicle (UAV). One of the UA V platforms of choice is the R5O unmanned helicopter, by Yamaha.The present version of the UAV platform is augmented with a camera system. This is enough for performing missions like site mapping, terrain exploration, in which the helicopter motion can be rather slow. But in tracking missions, and obstacle avoidance scenarios, involving high-speed helicopter motion, robust performance for the visual-servoing scheme is desired. Robustness in this case is twofold: 1) w.r.t time delays introduced by the image processing; and 2) w.r.t disturbances, parameter uncertainties and unmodeled dynamics which reflect on the feature position in the image, and the camera pose.With this goal in mind, we propose to explore the possibilities for the design of fuzzy controllers, achieving stability, robust and minimal-cost performance w.r.t time delays and unstructured uncertainties for image feature tracking, and test a control solution in both simulation and on real camera platforms. Common to both are model-based design by the use of nonlinear control approaches. The performance of these controllers is tested in simulation using the nonlinear geometric model of a pin-hole camera. Then we implement and test the reSUlting controller on the camera platform mounted on the UAV.

[14] Full text  Jonas Kvarnstr√∂m. 2005.
TALplanner and other extensions to Temporal Action Logic.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #937. Link√∂pings universitet. 302 pages. ISBN: 91-85297-75-5.

Though the exact definition of the boundary between intelligent and non-intelligent artifacts has been a subject of much debate, one aspect of intelligence that many would deem essential is <em>deliberation</em>: Rather than reacting \"instinctively\" to its environment, an intelligent system should also be capable of <em>reasoning</em> about it, reasoning about the effects of actions performed by itself and others, and creating and executing plans, that is, determining which actions to perform in order to achieve certain goals. True deliberation is a complex topic, requiring support from several different sub-fields of artificial intelligence. The work presented in this thesis spans two of these partially overlapping fields, beginning with <em>reasoning about action and change</em> and eventually moving over towards <em>planning</em>.The qualification problem relates to the difficulties inherent in providing, for each action available to an agent, an exhaustive list of all qualifications to the action, that is, all the conditions that may prevent the action from being executed in the intended manner. The first contribution of this thesis is a framework for <em>modeling qualifications</em> in Temporal Action Logic (TAL).As research on reasoning about action and change proceeds, increasingly complex and interconnected domains are modeled in increasingly greater detail. Unless the resulting models are structured consistently and coherently, they will be prohibitively difficult to maintain. The second contribution is a framework for <em>structuring TAL domains</em> using object-oriented concepts.Finally, the second half of the thesis is dedicated to the task of <em>planning</em>. TLplan pioneered the idea of using domain-specific control knowledge in a temporal logic to constrain the search space of a forward-chaining planner. We develop a new planner called TALplanner, based on the same idea but with fundamental differences in the way the planner verifies that a plan satisfies control formulas. T ALplanner generates concurrent plans and can take resource constraints into account. The planner also applies several new automated domain analysis techniques to control formulas, further increasing performance by orders of magnitude for many problem domains.

2004
[13] Peter Bunus. 2004.
Debugging techniques for equation-based languages.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #873. Link√∂ping University. 243 pages. ISBN: 91-7373-941-3.

Mathematical modeling and simulation of complex physical systems is emerging as a key technology in engineering. Modern approaches to physical system simulation allow users to specify simulation models with the help of equation-based languages. Such languages have been designed to allow automatic generation of efficient simulation code from declarative specifications. Complex simulation models are created by combining available model components from user-defined libraries. The resulted models are compiled in a simulation environment for efficient execution.The main objective of this thesis work is to develop significantly improved declarative debugging techniques for equation-based languages. Both static and dynamic debugging methods have been considered in this context.A typical problem which often appears in physical system modeling and simulation is when too many/few equations are specified in a systems of equations. This leads to a situation where the simulation model is inconsistent and therefore cannot be compiled and executed. The user should deal with over- and under-constrained situation by identifying the minimal set of equations or variables that should be removed/added from the equation system in order to make the remaining set of equations solvable.In this context, this thesis proposes new methods for debugging over- and under-constrained systems of equations. We propose a methodology for detecting and repairing over- and underconstrained situations based on graph theoretical methods. Components and equations that cause the irregularities are automatically isolated, and meaningful error messages for the user are presented. A major contribution of the thesis is our approach to reduce the potentially large number of error fixing alternatives by applying filtering rules extracted from the modeling language semantics.The thesis illustrates that it is possible to localize and repair a significant number of errors during static analysis of an object-oriented equation-based model without having to execute the simulation model. In this way certain numerical failures can be avoided later during the execution process. The thesis proves that the result of structural static analysis performed on the underlying system of equations can effectively be used to statically debug real models.A semi-automated algorithmic debugging framework is proposed for dynamic fault localization and behavior verification of simulation models. The run-time debugger is automatically invoked when an assertion generated from a formal specification of the simulation model behavior is violated. Analysis of the execution trace decorated with data dependency graph in the form of the Block Lower Triangular Dependency Graph (BLTDG) extracted from the language compiler is the basis of the debugging algorithm proposed in the thesis. We show how program slicing and dicing performed at the intermediate code level combined with assertion checking techniques to a large extent can automate the error finding process and behavior verification for physical system simulation models. Via an interactive session, the user is able to repair errors caused by incorrectly specified equations and incorrect parameter values.The run-time algorithmic debugger described in the thesis represents the first major effort in adapting automated debugging techniques to equation-based languages. To our knowledge none of the existing simulation environments associated with such languages provides support for run-time declarative automatic debugging.This thesis makes novel contributions to the structure and design of easy-to-use equation-based modeling and simulation environments and illustrates the role of structural static analysis and algorithmic automated debugging in this setting. The scope and feasibility of the approach is demonstrated by a prototype environment

2003
[12] Full text  Anders Arpteg. 2003.
Adaptive Semi-structured Information Extraction.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #1000. Institutionen f√∂r datavetenskap. 85 pages. ISBN: 91-7373-589-2.
Note: Report code: LiU-Tek-Lic-2002:73.

The number of domains and tasks where information extraction tools can be used needs to be increased. One way to reach this goal is to construct user-driven information extraction systems where novice users are able to adapt them to new domains and tasks. To accomplish this goal, the systems need to become more intelligent and able to learn to extract information without need of expert skills or time-consuming work from the user.The type of information extraction system that is in focus for this thesis is semistructural information extraction. The term semi-structural refers to documents that not only contain natural language text but also additional structural information. The typical application is information extraction from World Wide Web hypertext documents. By making effective use of not only the link structure but also the structural information within each such document, user-driven extraction systems with high performance can be built.The extraction process contains several steps where different types of techniques are used. Examples of such types of techniques are those that take advantage of structural, pure syntactic, linguistic, and semantic information. The first step that is in focus for this thesis is the navigation step that takes advantage of the structural information. It is only one part of a complete extraction system, but it is an important part. The use of reinforcement learning algorithms for the navigation step can make the adaptation of the system to new tasks and domains more user-driven. The advantage of using reinforcement learning techniques is that the extraction agent can efficiently learn from its own experience without need for intensive user interactions.An agent-oriented system was designed to evaluate the approach suggested in this thesis. Initial experiments showed that the training of the navigation step and the approach of the system was promising. However, additional components need to be included in the system before it becomes a fully-fledged user-driven system.

2002
[11] Full text  Peter Bunus. 2002.
Debugging and Structural Analysis of Declarative Equation-Based Languages.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #964. Institutionen f√∂r datavetenskap. 156 pages. ISBN: 91-7373-382-2.
Note: Report code: LiU-Tek-Lic-2002:37.

A significant part of the software development effort is spent on detecting deviations between software implementations and specifications, and subsequently locating the sources of such errors. This thesis illustrates that is possible to identify a significant number of errors during static analysis of declarative object-oriented equation-based modeling languages that are typically used for system modeling and simulation. Detecting anomalies in the source code without actually solving the underlying system of equations provides a significant advantage: a modeling error can be corrected before trying to get the model compiled or embarking on a computationally expensive symbolic or numerical solution process. The overall objective of this work is to demonstrate that debugging based on static analysis techniques can considerably improve the error location and error correcting process when modeling with equation-based languages.A new method is proposed for debugging of over- and under-constrained systems of equations. The improved approach described in this thesis is to perform the debugging process on the flattened intermediate form of the source code and to use filtering criteria generated from program annotations and from the translation rules. Each time when an error is detected in the intermediate code and the error fixing solution is elaborated, the debugger queries for the original source code before presenting any information to the user. In this way, the user is exposed to the original language source code and not burdened with additional information from the translation process or required to inspect the intermediate code.We present the design and implementation of debugging kernel prototypes, tightly integrated with the core of the optimizer module of a Modelica compiler, including details of the novel framework required for automatic debugging of equation-based languages.This thesis establishes that structural static analysis performed on the underlying system of equations from object-oriented mathematical models can effectively be used to statically debug real Modelica programs. Most of our conclusions developed in this thesis are also valid for other equation-based modeling languages.

[10] Full text  Patrik Haslum. 2002.
Prediction as a Knowledge Representation Problem: A Case Study in Model Design.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #942. Institutionen f√∂r datavetenskap. 106 pages. ISBN: 91-7373-331-8.
Note: Report code: LiU-Tek-Lic-2002:15.
Link to Ph.D. Thesis: http://urn.kb.se/resolve?urn=urn:nbn:se:...

The WITAS project aims to develop technologies to enable an Unmanned Airial Vehicle (UAV) to operate autonomously and intelligently, in applications such as traffic surveillance and remote photogrammetry. Many of the necessary control and reasoning tasks, e.g. state estimation, reidentification, planning and diagnosis, involve prediction as an important component. Prediction relies on models, and such models can take a variety of forms. Model design involves many choices with many alternatives for each choice, and each alternative carries advantages and disadvantages that may be far from obvious. In spite of this, and of the important role of prediction in so many areas, the problem of predictive model design is rarely studied on its own.In this thesis, we examine a range of applications involving prediction and try to extract a set of choices and alternatives for model design. As a case study, we then develop, evaluate and compare two different model designs for a specific prediction problem encountered in the WITAS UAV project. The problem is to predict the movements of a vehicle travelling in a traffic network. The main difficulty is that uncertainty in predictions is very high, du to two factors: predictions have to be made on a relatively large time scale, and we have very little information about the specific vehicle in question. To counter uncertainty, as much use as possible must be made of knowledge about traffic in general, which puts emphasis on the knowledge representation aspect of the predictive model design.The two mode design we develop differ mainly in how they represent uncertainty: the first uses coarse, schema-based representation of likelihood, while the second, a Markov model, uses probability. Preliminary experiments indicate that the second design has better computational properties, but also some drawbacks: model construction is data intensive and the resulting models are somewhat opaque.

[9] Full text  Bourhane Kadmiry. 2002.
Fuzzy Control for an Unmanned Helicopter.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #938. Institutionen f√∂r datavetenskap. 108 pages. ISBN: 91-7373-313-X.
Note: Report code: LiU-Tek-Lic-2002:11. The format of the electronic version of this thesis differs slightly from the printed one: this is due mainly to font compatibility. The figures and body of the thesis are remaining unchanged.

The overall objective of the Wallenberg Laboratory for Information Technology and Autonomous Systems (WITAS) at Link√∂ping University is the development of an intelligent command and control system, containing vision sensors, which supports the operation of a unmanned air vehicle (UAV) in both semi- and full-autonomy modes. One of the UAV platforms of choice is the APID-MK3 unmanned helicopter, by Scandicraft Systems AB. The intended operational environment is over widely varying geographical terrain with traffic networks and vehicle interaction of variable complexity, speed, and density.The present version of APID-MK3 is capable of autonomous take-off, landing, and hovering as well as of autonomously executing pre-defined, point-to-point flight where the latter is executed at low-speed. This is enough for performing missions like site mapping and surveillance, and communications, but for the above mentioned operational environment higher speeds are desired. In this context, the goal of this thesis is to explore the possibilities for achieving stable ‚Äė‚Äėaggressive‚Äô‚Äô manoeuvrability at high-speeds, and test a variety of control solutions in the APID-MK3 simulation environment.The objective of achieving ‚Äė‚Äėaggressive‚Äô‚Äô manoeuvrability concerns the design of attitude/velocity/position controllers which act on much larger ranges of the body attitude angles, by utilizing the full range of the rotor attitude angles. In this context, a flight controller should achieve tracking of curvilinear trajectories at relatively high speeds in a robust, w.r.t. external disturbances, manner. Take-off and landing are not considered here since APIDMK3 has already have dedicated control modules that realize these flight modes.With this goal in mind, we present the design of two different types of flight controllers: a fuzzy controller and a gradient descent method based controller. Common to both are model based design, the use of nonlinear control approaches, and an inner- and outer-loop control scheme. The performance of these controllers is tested in simulation using the nonlinear model of APID-MK3.

2001
[8] Full text  Marcus Bj√§reland. 2001.
Model-based execution monitoring.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #688. Link√∂pings universitet. 153 pages. ISBN: 91-7373-016-5.

The task of monitoring the execution of a software-based controller in order to detect, classify, and recover from discrepancies between the actual effects of control actions and the effects predicted by a model, is the topic of this thesis. Model-based execution monitoring is proposed as a technique for increasing the safety and optimality of operation of large and complex industrial process controllers, and of controllers operating in complex and unpredictable environments (such as unmanned aerial vehicles).In this thesis we study various aspects of model-based execution monitoring, including the following:The relation between previous approaches to execution monitoring in Control Theory, Artificial Intelligence and Computer Science is studied and a common conceptual framework for design and analysis is proposed.An existing execution monitoring paradigm, <em>ontological control</em>, is generalized and extended. We also present a prototype implementation of ontological control with a first set of experimental results where the prototype is applied to an actual industrial process control system: The ABB STRESSOMETER cold mill flatness control system.A second execution monitoring paradigm, <em>stability-based execution monitoring</em>, is introduced, inspired by the vast amount of work on the \"stability\" notion in Control Theory and Computer Science.Finally, the two paradigms are applied in two different frameworks. First, in the \"hybrid automata\" framework, which is a state-of-the-art formal modeling framework for hybrid (that is, discrete+continuous) systems, and secondly, in the logical framework of GOLOG and the Situation Calculus.

[7] Full text  Joakim Gustafsson. 2001.
Extending temporal action logic.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #689. Link√∂pings universitet. 218 pages. ISBN: 91-7373-017-3.

An autonomous agent operating in a dynamical environment must be able to perform several \"intelligent\" tasks, such as learning about the environment, planning its actions and reasoning about the effects of the chosen actions. For this purpose, it is vital that the agent has a coherent, expressive, and well understood means of representing its knowledge about the world.Traditionally, all knowledge about the dynamics of the modeled world has been represented in complex and detailed action descriptions. The first contribution of this thesis is the introduction of domain constraints in TAL, allowing a more modular representation of certain kinds of knowledge.The second contribution is a systematic method of modeling different types of conflict handling that can arise in the context of concurrent actions. A new type of fluent, called influence, is introduced as a carrier from cause to actual effect. Domain constraints govern how influences interact with ordinary fluents. Conflicts can be modeled in a number of different ways depending on the nature of the interaction.A fundamental property of many dynamical systems is that the effects of actions can occur with some delay. We discuss how delayed effects can be modeled in TAL using the mechanisms previously used for concurrent actions, and consider a range of possible interactions between the delayed effects of an action and later occurring actions.In order to model larger and more complex domains, a sound modeling methodology is essential. We demonstrate how many ideas from the object-oriented paradigm can be used when reasoning about action and change. These ideas are used both to construct a framework for high level control objects and to illustrate how complex domains can be modeled in an elaboration tolerant manner.

1999
[6] Full text  Lars Karlsson. 1999.
Actions, interactions and narratives.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #593. Link√∂pings universitet. 222 pages. ISBN: 91-7219-534-7.

The area of reasoning about action and change is concerned with the formalization of actions and their effects as well as other aspects of inhabited dynamical systems. The representation is typically done in some logical language. Although there has been substantial progress recently regarding the frame problem and the ramification problem, many problems still remain. One of these problems is the representation of concurrent actions and their effects. In particular, the effects of two or more actions executed concurrently may be different from the union of the effects of the individual actions had they been executed in isolation. This thesis presents a language, TAL-C, which supports detailed and flexible yet modular descriptions of concurrent interactions. Two related topics, which both require a solution to the concurrency problem, are also addressed: the representation of effects of actions that occur with some delay, and the representation of actions that are caused by other actions.Another aspect of reasoning about action and change is how to describe higher-level reasoning tasks such as planning and explanation. In such cases, it is important not to just be able to reason about a specific narrative (course of action), but to reason about alternative narratives and their properties, to compare and manipulate narratives, and to reason about alternative results of a specific narrative. This subject is addressed in the context of the situation calculus, where it is shown how the standard version provides insufficient support for reasoning about alternative results, and an alternative version is proposed. The narrative logic NL is also presented; it is based on the temporal action logic TAL, where narratives are represented as first-order terms. NL supports reasoning about (I) metric time, (II) alternative ways the world can develop relative to a specific choice of actions, and (III) alternative choices of actions.

[5] Silvia Coradeschi. 1999.
Anchoring symbols to sensory data.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #611. Link√∂pings universitet. 136 pages. ISBN: 91-7219-623-8.

Intelligent agents embedded in physical environments need the ability to connect, or <em>anchor</em>, the symbols used to perform abstract reasoning to the physical entities which these symbols refer to. Anchoring must deal with indexical and objective references, definite and indefinite identifiers, and a temporary impossibility to perceive physical entities. Furthermore it needs to rely on sensor data which is inherently affected by uncertainty, and to deal with ambiguities. In this thesis, we outline the concept of anchoring and its functionalities. Moreover we define the general structure for an anchoring module and we present an implementation of the anchoring functionalities in two different domains: an autonomous airborne vehicle for traffic surveillance and a mobile ground vehicle performing navigation.

1998
[4] Full text  Marcus Bj√§reland. 1998.
Two Aspects of Automating Logics of Action and Change: Regression and Tractability.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #674. Link√∂pings universitet. 83 pages. ISBN: 91-7219-173-2.
Note: Thesis No 674. LiU-Tek-Lic 1998:09

The autonomy of an artificial agent (e.g. a robot) will certainly depend on its ability to perform \"intelligent\" tasks, such as learning, planning, and reasoning about its own actions and their effects on the enviroment, for example predicting the consequences of its own behaviour. To be able to perform these (and many more) tasks, the agent will have to represent its knowledge about the world.The research field \"Logics of Action Change\" is concerned with the modelling of agents and dynamical, changing environments with logics.In this thesis we study two aspects of automation of logics of action and change. The first aspect, regression, is used to \"reason backwards\", i.e. to start with the last time point in a description of a course of events, and moving backwards through these events, taking the effects of all actions into consideration. We discuss the consequences for regression of introducing nondeterministic actions, and provide the logic PMON with pre- and postdiction procedures. We employ the classical computer science tool, the weakest liberal precondition operator (wlp) for this, and show that logical entailment of PMON is equivalent to wlp computations.The second aspect is computational complexity of logics of action and change, which has virtually been neglected by the research community. We present a new and expressive logic, capable of expressing continuous time, nondeterministic actions, concurrency, and memory of actions. We show that satisfiability of a theory in this logic is NP-complete. Furthermore, we identify a tractable subset of the logic, and provide a sound, complete, and polynomial algorithm for satisfiability of the subset.

1991
[3] Patrick Doherty. 1991.
NML3: a non-monotonic formalism with explicit defaults.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #258. Link√∂pings tekniska h√∂gskola. 290 pages. ISBN: 91-7870-816-8.

The thesis is a study of a particular approach to defeasible reasoning based on the notion of an information state consisting of a set of partial interpretations constrained by an information ordering. The formalism proposed, called NML3, is a non-monotonic logic with explicit defaults and 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. (3) The use of the technique of preferential entailment to generate non-monotonic 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 the existing formalisms. By capitalizing on the distinction between tentative and ordinary conclusions, NML3 provides increased expressibility in comparison to many of the standard non-monotonic formalisms and greater flexibility in the representation of subtle aspects of default reasoning.In addition to NML3, a novel extension of the tableau-based proof technique is presented where a signed formula is tagged with a set of truth values rather than a single truth value. This is useful if the tableau-based proof technique is to be generalized to apply to the class of multi-valued logics. A refutation proof procedure may then be used to check logical consequence for the base logic used in NML3 and to provide a decision procedure for the propositional case of NML3.A survey of a number of non-standard logics used in knowledge representation is also provided. Various formalisms are analyzed in terms of persistence properties of formulas and their use of information structures.

1990
[2] Patrick Doherty. 1990.
A three-valued approach to non-monotonic reasoning.
Licentiate Thesis. In series: Link√∂ping Studies in Science and Technology. Thesis #230. Link√∂ping University. 117 pages. ISBN: 91-7870-672-6.

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.

1977
[1] Anders Haraldsson. 1977.
A program manipulation system based on partial evaluation.
PhD Thesis. In series: Link√∂ping Studies in Science and Technology. Dissertations #14. Link√∂pings universitet. 264 pages. ISBN: 91-7372-144-1.
Note: Date of defense not available.

Program manipulation is the task to perform transformations on program code, and is normally done in order to optimize the code with respect of the utilization of some computer resource. Partial evaluation is the task when partial computations can be performed in a program before it is actually executed. If a parameter to a procedure is constant a specialized version of that procedure can be generated if the constant is inserted instead of the parameter in the procedure body and as much computations in the code as possible are performed.A system is described which works on programs written in INTERLISP, and which performs partial evaluation together with other transformations such as beta-expansion and certain other optimization operations. The system works on full LISP and not only for a \"pure\" LISP dialect, and deals with problems occurring there involving side-effects, variable assignments etc. An analysis of a previous system, REDFUN, results in a list of problems, desired extensions and new features. This is used as a basis for a new design, resulting in a new implementation, REDFUN-2. This implementation, design considerations, constraints in the system, remaining problems, and other experience from the development and experiments with the system are reported in this paper.