In this paper, we present a search algorithm called real-time search for solving combinatorial optimization problems under real-time constraints. The problems we study are NP-hard and have good heuristic algorithms for generating feasible solutions. The algorithm we develop aims at finding the best possible solution in a given deadline. Since this objective is generally not achievable without first solving the problem, we use an alternative heuristic objective that looks for the solution with the best ascertained approximation degree. Our algorithm schedules a sequence of guided depth-first searches, each searching for a more accurate solution (based on the approximation degree set), or solutions deeper in the search tree (based on the threshold set), or a combination of both. Five versions of the RTS algorithm for setting approximation degrees and/or thresholds are formulated, evaluated, and analyzed. We develop an exponential model for characterizing the relationship between the app...

The goal of this research is to develop a systematic, integrated method of designing efficient search algorithms that solve optimization problems in real time. Search algorithms studied in this thesis comprise meta-control and primitive search. The class of optimization problems addressed are called combinatorial optimization problems, examples of which include many NP-hard scheduling and planning problems, and problems in operations research and artificial-intelligence applications. The problems we have addressed have a well-defined problem objective and a finite set of well-defined problem constraints. In this research, we use state-space trees as problem representations. The approach we have undertaken in designing efficient search algorithms is an engineering approach and consists of two phases: (a) designing generic search algorithms, and (b) improving by genetics-based machine learning methods parametric heuristics used in the search algorithms designed. Our approach is a systematic method that integrates domain knowledge, search techniques, and automated learning techniques for designing better search algorithms. Knowledge captured in designing one search algorithm can be carried over for designing new ones. iv ACKNOWLEDGEMENTS I express my sincere gratitude to all the people who have helped me in the course of my graduate study. My thesis advisor, Professor Benjamin W. Wah, was always available for discussions and encouraged me to explore new ideas. I am deeply grateful to the committee

This is an overview of the most recent published approaches to solving the handwriting recognition problem. This paper is aimed at clarifying the role of handwriting recognition in accordance with today's maturing technologies. It tries to list and clarify the components that build handwriting recognition and related technologies such as OCR (Optical Character Recognition) and Signature Verification. This paper could also be regarded as a survey of handwriting recognition and related topics with a rich list of references for the interested reader. Levels of practicality of use of this technology for different languages and cultures is also discussed. 1 Introduction As portable computers become more personal and are made smaller, they reach some physical limitations for having a keyboard. For pocket size computers (PDA's) one cannot use an efficient keyboard. For these computers alternative ways of man-machine communication are necessary. A most efficient way of solving this problem is...

Selecting a distributed communication system is a balancing act. Ease of use, efficiency of the final product, and future needs are not mutually exclusive considerations. Several questions spring to mind immediately. What are the requirements of the communication system? What is available to use? What are the requirements of the user? Software engineers desire software to have clean interfaces and to make any internal details inaccessible to the other components. Performance users want the software to be scalable, efficient, and easy to use, read, and debug. This paper examines four communication systems (ISIS, NMP, PVM, and Concert/C) from these two points of view. Several programs designed to test the performance of the communication system are used as examples for comparing features. These programs are neither definitive test programs nor do they have complicated communication structures. Rather, they are used to highlight potential problem areas and implementation differences. All ...

The protection of customer privacy is a fundamental issue in today's corporate marketing strategies. Not surprisingly, many research efforts have proposed new privacy-aware technologies. Among them, Hippocratic databases offer mechanisms for enforcing privacy rules in database systems for inter-organizational business processes (also known as virtual organizations). This paper extends these mechanisms to allow for hierarchical purposes, distributed authorizations and minimal disclosure supporting the business processes of virtual organizations that want to offer their clients a number of ways to fulfill a service. Specifically, we use a goal-oriented approach to analyze privacy policies of the enterprises involved in a business process. Based on the purpose hierarchy derived through a goal refinement process, we provide algorithms for determining the minimum set of authorizations needed to achieve a service. This allows us to automatically derive access control policies for an inter-organizational business process from the collection of privacy policies associated with different participating enterprises. By using effective on-line algorithms, the derivation of such minimal information can also be done on-the-fly by the customer wishing to access a service.

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Enterprise is the latest offering in integrated programming environments for distributed parallel processing. Enterprise is intended for parallel programming on a network of workstations. The analogy of a business organization or enterprise is used to describe the various parallel constructs (line, department, division, individual, receptionist, representative, individual, and service) offered. Each asset or stand-alone module intended for one processor is created from the user's familiar sequential code and the graph that describes the parallelism. Enterprise is designed to use standard C code. The appropriate low-level communication and synchronization code is inserted by Enterprise; changes to either resources or the type of parallelism desired are easily accommodated and involve little user involvement. This thesis presents four parallel algorithms that were developed using Enterprise: chaotic Gauss-Seidel, block matrix multiplication, transitive closure and alpha-beta search. The...

There has been a considerable amount of research into the provision of explicit representation of control regimes for resolution-based theorem provers.

The scheduling of programs on parallel hardware is investigated in order to minimize the response time of the resulting system. In particular the scheduling problem considered in this paper includes---next to the search for an optimal mapping of the tasks and their sequence of execution---also the search for an optimal configurationof the parallel hardware. An approach for the simultaneous optimization of all three components using genetic algorithms is presented and its performance is evaluated in comparison with an exact reference method based on an branch-and-bound-with-underestimates algorithm. The comparison is based on a large set of problem instances and includes regular task graphs with varying structure and scalable size, which had to be mapped onto a configurable parallel hardware consisting of 4 up to 16 transputers respectively. Small problem instances with less than 8 1 tasks can be solved by both solution methods. For larger problem instances the reference method fails d...

In this paper, we propose a novel search algorithm called band search that generalizes guided depth-first and best-first searches. The search allocates a band of at most W nodes in each level of the search tree for storing active nodes in that level, D priority lists, one for each level, for storing overflow nodes, and D counters, one for each level, for keeping track of and to limit the degree of backtracking allowed. The algorithm has three major features: a) it selects for expansion in a best-first fashion from all nodes in the bands, b) it moves nodes from an overflow list into the corresponding band in a depth-first fashion, and c) it restricts backtracking so that at most W nodes in a level are fully searched before allowing new nodes in this level into the band. The algorithm specializes to be a guided depth-first search (GDFS) when W is one, and a best-first search (BFS) when W is unlimited. By choosing W appropriately, we show empirically that the algorithm can often outperf...