Formal methods reality check: industrial usage

Based on a systematic survey and analysis of the use of formal methods in the development of a dozen industrial applications, we summarize the methods being used, characterize the styles of industrial usage, and provide recommendations for evolutionary enhancements to the technology base of formal methods. The industrial applications ranged from reverse engineering to system certification; code scale ranges from 1 KLOC to 10 KLOC's. Applications included a software infrastructure for oscilloscopes; a shutdown system for a nuclear generating station; a train protection system; an airline collision avoidance system; an engine monitoring system for shipboard engines; attitude control of satellites; security properties of both a smartcard device and a network; arithmetic units; transaction processing; a real-time database for a medical instrument; and a restructuring program for COBOL     

Engineering applications of neural networks

This paper describes several prototypical applications of neural network technology to engineering problems. The applications were developed by the authors as part of a graduate-level course taught at the University of Illinois at Urbana-Champaign by the first author (now at Carnegie Mellon University). The applications are: an adaptive controller for building thermal mass storage; an adaptive controller for a combine harvester; an interpretation system for non-destructive evaluation of masonry walls; a machining feature recognition system for use in process planning; an image classification system for classifying land coverage from satellite or high-altitude images; and a system for designing the pumping strategy for contaminated groundwater remediation. These applications are representative of many of the engineering problems for which neural networks are applicable: adaptive control, feature recognition, and design.     

Expert system for selecting expert system shells

A prototype expert system is described that advises end-users in the selection of a suitable development environment for small- to medium-scale expert system applications. The system, running on a microcomputer, assesses the suitability of an application as a whole for expert systems techniques and recommends the five ‘best’ products from its knowledge base of 42 products. The paper takes a case-study approach, using the system itself as a recursive discussion example, applying some of the concepts involved in building an expert system. It describes the operation of the system and suggests improvements; it includes a feature list for classifying expert system shells.     

Robust precision attitude tracking of an uncertain rigid spacecraft based on regulation theory

This paper explores regulation theory for the design of robust precision attitude tracking of an uncertain rigid spacecraft with external disturbances. Focusing on the attitude system in terms of unit quaternions with an unknown inertia matrix and unmodeled input disturbances, we first introduce specific nonlinear logic such that the resultant error‐quaternion system has an input‐to‐state stability property. Then, we establish an attitude deviation system with an output feedback normal form that has a strict vector relative degree of unity. This enables us to achieve robust output regulation based on an internal model. In particular, we can construct a high‐gain stabilizer for the relevant augmented system. As a major consequence, our study achieves not only precision attitude tracking with exponential convergence but also the input‐to‐state stability disturbance attenuation for the closed‐loop system. Finally, we show extensive simulation and experimental results to illustrate the approach.     

Multi-driver agent-based traffic simulation systems for evaluating the effects of advanced driver assistance systems on road traffic accidents

A recent investigation revealed that there is a substantiated need for the development of a micro-simulation system designed for traffic safety assessment. This paper describes the development of a road traffic simulation system, which uses a ‘nanoscopic model’ of driver behaviour and an integrated analysis-evaluation system designed for traffic safety assessment. The primary focus is on estimating the effects of an advanced driver assistance system thereby reducing traffic accidents. The effectiveness and validity of the present system are demonstrated through comparison with measured traffic data. This paper also proposes algorithms embedded in a ‘driver-agent’, for recognising driver’s intentions regarding choosing steering-control modes, lateral control tasks, and the driving mood. This is because the driver assistance systems need to recognise the driver’s intention when choosing steering-control. The results of a simulation study, using the data drawn from actual driving, show that the systems would achieve a high recognition capability. As an example of how driving mood recognition applies to driver assistance systems, an advanced steering system and the adaptability to the driver’s mood, have also been presented.     

Optimal sequencing of warm standby elements

Warm standby redundancy has been used as an effective design technique for improving the reliability of a system while achieving the compromise between restoration cost and operation cost of standby elements. This paper considers the optimal standby element sequencing problem (SESP) for 1-out-of-N: G heterogeneous warm-standby systems. Given the desired redundancy level and a fixed set of element choices, the objective of the optimal system design is to select the initiation sequence of the system elements so as to minimize the expected mission cost of the system while providing a certain level of system reliability. Based on a discrete approximation of time-to-failure distributions of the system elements, the system reliability and expected mission cost are evaluated using an iterative procedure. A genetic algorithm is used as an optimization tool for solving the formulated SESP problem for 1-out-of-N: G warm-standby systems with non-identical elements. As illustrated through examples, results generated using the suggested methodology can facilitate the system reliability versus cost trade-off study, which can further assist in the decision making about the best standby policy for fault-tolerant system designs.     

Investigation of a one-channel queueing system with an unlimited queue and the markovian anticipatory switching

Acondition of stability on the second approximation is obtained for a pulse system with anticipatory switching based on the diffusive approximation of normalized deviations of solutions of the system from the solution of an averaged system. The theoretical results obtained are used for investigating a one-channel queueing system with an unlimited queue. Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 168–173, July–August, 2000.     

A test case generation approach for conformance testing of SDL systems

This paper presents an approach for automatic executable test case and test sequence generation for a protocol modeled by an SDL system. Our methodology uses a unified method which tests an Extended Finite State Machine (EFSM) based system by using control and data flow techniques. To test an SDL system, it extracts an EFSM from each process then the system is tested by incrementally computing a partial product for each EFSM C, taking into account only transitions which influence (or are influenced by) C, and generating test cases for it. This process ends when the coverage achieved by the generated test cases is satisfactory or when the partial products for all EFSMs are tested. Experimental results show that this method can be applied to systems of practical size.     

Reliable and efficient landmark-based localization for mobile robots

This paper describes an efficient and robust localization system for indoor mobile robots and AGVs. The system utilizes a sensor that measures bearings to artificial landmarks, and an efficient triangulation method. We present a calibration method for the system components and overcome typical problems for sensors of the mentioned type, which are localization in motion and incorrect identification of landmarks. The resulting localization system was tested on a mobile robot. It consumes less than 4% of a Pentium4 3.2 GHz processing power while providing an accurate and reliable localization result every 0.5 s. The system was successfully incorporated within a real mobile robot system which performs many other computational tasks in parallel.     

APPLICATION OF H∞ CONTROL AND CLOSED LOOP IDENTIFICATION TO A MAGNETIC LEVITATION SYSTEM

A systematic procedure for modeling and robust control of a multivariable magnetic levitation system is described. Our previous study revealed that an observer-based LQ controller can stabilize the system, but generates spillovers in the presence of an impulse disturbance. To solve this problem, we apply an H_∞ control to suppress the spillovers caused by unmodeled dynamics which we estimate using closed loop identification. First, an exactly linearized model is obtained to compensate for nonlinearities in the system, followed by estimation of the unmodeled dynamics using closed loop identification. Second, this information is used to design a two degree of freedom H_∞ servo system for suppressing the spillover while tracking a step reference input. Finally, the desired robust performance of the resulting servo system is confirmed theoretically by γ-analysis and also experimentally.     

Multi-access system with many users: Stability and metastability

A model of random multi-access system with an ALOHA-type protocol is analyzed when the number N of users is large and the system is overloaded. In the limit as N → ∞, the behavior of the system is described by a nonrandom dynamical system. We give a condition for the dynamical system to have an attractive fixed point and outline cases of several fixed points. The presence of several fixed points indicates that the finite system may exhibit a metastability phenomenon.     

A batch arrival queue under randomised multi-vacation policy with unreliable server and repair

This article examines an M^[x]/G/1 queueing system with an unreliable server and a repair, in which the server operates a randomised vacation policy with multiple available vacations. Upon the system being found to be empty, the server immediately takes a vacation. If there is at least one customer found waiting in the queue upon returning from a vacation, the server will be activated for service. Otherwise, if no customers are waiting for service at the end of a vacation, the server either remains idle with probability p or leaves for another vacation with probability 1???p. When one or more customers arrive when the server is idle, the server immediately starts providing service for the arrivals. It is possible that an unpredictable breakdown may occur in the server, in which case a repair time is requested. For such a system, we derive the distributions of several important system characteristics, such as the system size distribution at a random epoch and at a departure epoch, the system size distribution at the busy period initiation epoch, and the distribution of the idle and busy periods. We perform a numerical analysis for changes in the system characteristics, along with changes in specific values of the system parameters. A cost effectiveness maximisation model is constructed to show the benefits of such a queueing system.     

RBE: A Rule-by-example Active Database System

In an active database system, rules are used to monitor and respond to events that happen inside the database. This paper presents the implementation of an active database system called RBE. The system loosely couples an OPS5 production system and an INGRES database management system to efficiently monitor databases on complex conditions. In this system, atable-based Rule-By-Example (RBE) language, is designed. The internal representations of the RBE rule language are production rules; therefore, rules can be stored, managed and tested efficiently by using the well-developed pattern matching algorithm in a production system. In other words, the system applies a production system and a special production system program to the task of query rewrite trigger processing. Moreover, a user-friendly interface is used to loosely couple the OPS5 rule system with the INGRES DBMS. The architecture used in this system shows the applicability of constructing an active database system by integrating any production system and any database system. Moreover, the proposed technique could be used as an implementation method for a query-rewrite rule system inside a DBMS server, not using a layered approach. © 1997 by John Wiley & Sons, Ltd.     

Installation and operation of a multivariable ship boiler control system

A multivariable control system that is a part of an integrated, computer-based machinery control system is installed on board a 285000 tdw tanker. Experiences with the installation and operation of the multivariable control system will be presented, and a comparison between the multivariable system and the conventional back-up controller will be made. This paper is a natural continuation of an article which appeared in Automatica12, pp. 211–224 titled ‘The design of a multivariable control system for a ship boiler’.     

Input-to-State Stability for Nonlinear Time-Varying Systems via Averaging

 We introduce two definitions of an averaged system for a time-varying ordinary differential equation with exogenous disturbances (“strong average” and “weak average”). The class of systems for which the strong average exists is shown to be strictly smaller than the class of systems for which the weak average exists. It is shown that input-to-state stability (ISS) of the strong average of a system implies uniform semi-global practical ISS of the actual system. This result generalizes the result of [TPA] which states that global asymptotic stability of the averaged system implies uniform semi-global practical stability of the actual system. On the other hand, we illustrate by an example that ISS of the weak average of a system does not necessarily imply uniform semi-global practical ISS of the actual system. However, ISS of the weak average of a system does imply a weaker semi-global practical “ISS-like” property for the actual system when the disturbances w are absolutely continuous and . ISS of the weak average of a system is shown to be useful in a stability analysis of time-varying cascaded systems. Date received: April 6, 1999. Date revised: April 11, 2000.