3134095
Supervisory Control of Real-Time Systems Using Prioritized Synchronization
The theory of supervisory control of discrete event systems is extended to the real-time setting. The real-time behavior of a system is represented by the set of all possible timed traces of the system. This is alternatively specified using timed automata where each transition is associated with an event occurrence time set during which time the transition can occur. Our model for time is more general in that the time advances continuously as compared to a model where time advances discretely. We extend the notion of prioritized synchronous composition to the real-time setting to use it as the control mechanism. It is shown that a suitable extension of the controllability condition to the real-time setting yields a condition for the existence of a supervisor achieving a desired timed behavior. Although the real-time controllability is similar in form to its untimed counterpart, they are different in the sense that one does not imply the other and vice-versa.
6842097
Automated control synthesis for an assembly line using discrete event system control theory
The design of logic controllers for event-driven systems continue to rely largely on intuitive methods rather than on formal techniques. This approach results in a control code that requires extensive verification, is hard to maintain and modify, and may even fail at times. Supervisory control theory (SCT) provides a formal approach to logic control synthesis. In order to demonstrate the usefulness of the supervisory control theory in manufacturing systems, an educational test-bed that simulates an automated car assembly line has been built using LEGO/spl reg/ blocks. Finite state machines (FSMs) are used for modeling operations of the assembly line, and for the specifications that accomplish the task of successfully completing the assembly repeatedly. Using the technique of SCT, we derive a supervisor that enforces the specifications while offering the maximum flexibility of assembly. Subsequently a controller is extracted from the maximally permissive supervisor for the purpose of implementing the control by selecting, when possible, at most one controllable event from among the ones allowed by the supervisor. Testing to check the correctness of the control code is reduced, since the controller is guaranteed to enforce the specifications.
9294393
Decentralized control of discrete event systems with specializations to local control and concurrent systems
The decentralized supervisory control problem of discrete event systems under partial observation is studied in this paper. The main result of the paper is a necessary and sufficient condition for the existence of decentralized supervisors for ensuring. That the controlled behavior of the system lies in a given range. The contribution of the paper is (1) our setting of decentralized control generalizes the prior ones; (2) we present an alternative approach for solving the decentralized control problem, which leads to computational saving for concurrent systems and certain other systems; and (3) our generalized formulation and its solution lets us extend several of the existing results reported previously. The results of our paper are illustrated by an example of a simple manufacturing system.
13974246
Decentralized failure diagnosis of discrete event systems
By decentralized diagnosis we mean diagnosis using multiple diagnosers, each possessing its own set of sensors, without involving any communication among diagnosers or to any coordinators. The notion of decentralized diagnosis is formalized by introducing the notion of codiagnosability that requires that a failure be detected by one of the diagnosers within a bounded delay. Algorithms of complexity polynomial in the size of the system and the nonfault specification are provided for: 1) testing codiagnosability, 2) computing the bound in delay of diagnosis, 3) offline synthesis of individual diagnosers, and 4) online diagnosis using them. The notion of codiagnosability and the above algorithms are initially presented in a setting of a specification language (violation of which represents a fault) and are later specialized to the case where faults are modeled as the occurrences of certain events. The notion of strong codiagnosability is also introduced to capture the ability of being certain about both the failure as well as the nonfailure conditions in a system within a bounded delay.
21072857
Computing dynamic slices of concurrent object-oriented programs
We propose a novel dynamic program slicing technique for concurrent object-oriented programs. Our technique uses a Concurrent System Dependence Graph (CSDG) as the intermediate program representation. We mark and unmark the edges in the CSDG appropriately as and when the dependencies arise and cease during run-time. We mark an edge when its associated dependence exists and unmark an edge when the dependence ceases to exist. Our approach eliminates the use of trace files. Another advantage of our approach is that when a request for a slice is made, it is already available. This appreciably reduces the response time of slicing commands.
16795084
Analysis of a Multiobjective Evolutionary Algorithm on the 0-1 knapsack problem
Multiobjective Evolutionary Algorithms (MOEAs) are increasingly being used for effectively solving many real-world problems, and many empirical results are available. However, theoretical analysis is limited to a few simple toy functions. In this work, we select the well-known knapsack problem for the analysis. The multiobjective knapsack problem in its general form is NP-complete. Moreover, the size of the set of Pareto-optimal solutions can grow exponentially with the number of items in the knapsack. Thus, we formalize a (1 + e)-approximate set of the knapsack problem and attempt to present a rigorous running time analysis of a MOEA to obtain the formalized set. The algorithm used in the paper is based on a restricted mating pool with a separate archive to store the remaining population; we call the algorithm a Restricted Evolutionary Multiobjective Optimizer (REMO). We also analyze the running time of REMO on a special bi-objective linear function, known as LOTZ (Leading Ones : Trailing Zeros), whose Pareto set is shown to be a subset of the knapsack. An extension of the analysis to the Simple Evolutionary Multiobjective Optimizer (SEMO) is also presented. A strategy based on partitioning of the decision space into fitness layers is used for the analysis.
15398191
Precise static type analysis for object oriented programs
A precise static type analysis is important to make available dynamic aspects of object-oriented programs (OOPs) approximately known at compile-time. Many techniques have been proposed for static type analysis depending upon the tradeoff of cost and precision; the techniques may generate spurious possible types for a particular dynamic dispatch which makes the static type analysis imprecise. In this paper, we propose a symbolic execution based type analysis technique that analyzes the dynamic type inter-procedurally by keeping the flow of the program in consideration. We analyze test cases with different class hierarchies. The proposed technique was capable to resolve the target method for most of the dynamic dispatches at reduced computational cost.
13241097
Dictionary based code compression for variable length instruction encodings
Most of the work done in the field of machine code compression is for fixed length instruction encodings. In this work we apply code compression on variable length instruction set processors whose encodings are already optimized to a certain extent with respect to their usages. We develop a dictionary based algorithm which utilizes unused encoding space of an instruction set architecture to encode code-words, and addresses issues arising out of variable length instructions. We test the algorithm with a RISC processor and include results for compression and performance in terms of cycle-counts and memory accesses respectively. We also present an efficient scheme for searching relocated branch addresses and analyze its performance.
9633354
Real-time personalized sports video filtering and summarization
We demonstrate a real-time fully automated software system for filtering important events in sports video. Events represent occurrences of actions or state changes in video content. In the current prototype, we demonstrate detection of pitching in baseball and serving in tennis. For wireless video applications, we propose and apply a unique notion of content-based adaptive streaming,in which video encoding rate and media modality is dynamically varied according to the event filtering results. Our system includes an event detection module, an adaptive encoding module, and a buffer management module for adaptive streaming. We achieve the real-time performance by exploring compressed-domain techniques and multi-stage multi-resolution content-analysis processes.