State (computer science)

About: State (computer science) is a(n) research topic. Over the lifetime, 24436 publication(s) have been published within this topic receiving 225733 citation(s).

Hybrid Automata: An Algorithmic Approach to the Specification and Verification of Hybrid Systems

Abstract: We introduce the framework of hybrid automata as a model and specification language for hybrid systems. Hybrid automata can be viewed as a generalization of timed automata, in which the behavior of variables is governed in each state by a set of differential equations. We show that many of the examples considered in the workshop can be defined by hybrid automata. While the reachability problem is undecidable even for very restricted classes of hybrid automata, we present two semidecision procedures for verifying safety properties of piecewiselinear hybrid automata, in which all variables change at constant rates. The two procedures are based, respectively, on minimizing and computing fixpoints on generally infinite state spaces. We show that if the procedures terminate, then they give correct answers. We then demonstrate that for many of the typical workshop examples, the procedures do terminate and thus provide an automatic way for verifying their properties.

Principles and methods of testing finite state machines-a survey

Abstract: With advanced computer technology, systems are getting larger to fulfill more complicated tasks: however, they are also becoming less reliable. Consequently, testing is an indispensable part of system design and implementation; yet it has proved to be a formidable task for complex systems. This motivates the study of testing finite stare machines to ensure the correct functioning of systems and to discover aspects of their behavior. A finite state machine contains a finite number of states and produces outputs on state transitions after receiving inputs. Finite state machines are widely used to model systems in diverse areas, including sequential circuits, certain types of programs, and, more recently, communication protocols. In a testing problem we have a machine about which we lack some information; we would like to deduce this information by providing a sequence of inputs to the machine and observing the outputs produced. Because of its practical importance and theoretical interest, the problem of testing finite state machines has been studied in different areas and at various times. The earliest published literature on this topic dates back to the 1950's. Activities in the 1960's mid early 1970's were motivated mainly by automata theory and sequential circuit testing. The area seemed to have mostly died down until a few years ago when the testing problem was resurrected and is now being studied anew due to its applications to conformance testing of communication protocols. While some old problems which had been open for decades were resolved recently, new concepts and more intriguing problems from new applications emerge. We review the fundamental problems in testing finite state machines and techniques for solving these problems, tracing progress in the area from its inception to the present and the stare of the art. In addition, we discuss extensions of finite state machines and some other topics related to testing.

State models for monitoring processes

Abstract: A system and method for preparing, using and displaying a state model of a process, as an industrial or business process, as a sequence of discrete steps. The state model defines the behavior of the logical objects making up a process model of the process as a set of permitted states and a set of permitted transitions between the permitted states. The method involves creating a state model (61) with certain parameters, a Create/Modify State Transition for a State Model (63) and Associate State Transition with Rules and Conditions (65). These rules are inputted into a graphical user interface which causes appropriate rules to be extracted from a database (67). They are assembled into a state machine execution engine (69) and implemented (70) to produce an enforced state model on targeted business objects (71) and the target business object is enabled (73).

Symbolic model checking: an approach to the state explosion problem

Abstract: Finite state models of concurrent systems grow exponentially as the number of components of the system increases. This is known widely as the state explosion problem in automatic verification, and has limited finite state verification methods to small systems. To avoid this problem, a method called symbolic model checking is proposed and studied. This method avoids building a state graph by using Boolean formulas to represent sets and relations. A variety of properties characterized by least and greatest fixed points can be verified purely by manipulations of these formulas using Ordered Binary Decision Diagrams. Theoretically, a structural class of sequential circuits is demonstrated whose transition relations can be represented by polynomial space OBDDs, though the number of states is exponential. This result is born out by experimental results on example circuits and systems. The most complex of these is the cache consistency protocol of a commercial distributed multiprocessor. The symbolic model checking technique revealed subtle errors in this protocol, resulting from complex execution sequences that would occur with very low probability in random simulation runs. In order to model the cache protocol, a language was developed for describing sequential circuits and protocols at various levels of abstraction. This language has a synchronous dataflow semantics, but allows nondeterminism and supports interleaving processes with shared variables. A system called SMV can automatically verify programs in this language with respect to temporal logic formulas, using the symbolic model checking technique. A technique for proving properties of inductively generated classes of finite state systems is also developed. The proof is checked automatically, but requires a user supplied process called a process invariant to act as an inductive hypothesis. An invariant is developed for the distributed cache protocol, allowing properties of systems with an arbitrary number of processors to be proved. Finally, an alternative method is developed for avoiding the state explosion in the case of asynchronous control circuits. This technique is based on the unfolding of Petri nets, and is used to check for hazards in a distributed mutual exclusion circuit.