This paper proposes the Total High Performance Time as a performance-related reliability measure in degradable/recoverable real-time systems. This measure reflects the effect of system behavior in pending states that are temporary states between the normal state and degraded states where the system operates in a degraded mode as a consequence of component failures. Such systems have to perform not only normal procedures but also error/recovery procedures in pending states, so the performance there is lower than that in the degraded states. In real-time systems, if performance is less than a lower limit, the response time for on-line transactions cannot meet the deadline. The consequences of failing to meet the deadline could be system failure. Therefore, the system reliability is affected significantly by whether the performance there is higher than the lower limit or not. A state where the level of performance is higher than the lower limit is called a High Performance State. We define the Total High Performance Time as the total time that the system spends operating in High Performance States. Moreover, this paper explains how to utilize the Total High Performance Time in system design. We model a method of controlling a system in pending states by using Extended Stochastic Petri Nets and obtain the characteristics necessary for evaluating the Total High Performance Time by analyzing the model. This approach is applied to a storage system that controls mirrored disks, and shown to be helpful for designing a method of controlling a system in pending states, which has been considered difficult because of the trade-off between performance and reliability.

The structural necessary and sufficient condition for "the transition-liveness means the place-liveness and vice-versa" of a subclass NII of general Petri nets is given as "the place and transition live Petri net, or PTL net, ÑII". Furthermore, "the one-token-condition Petri net, or OTC net, II" which means that every MSDL (minimal structural deadlock) is "transition and place live" under at least one initial token, i.e., II is "transition and place live" under the above initial marking. These subclasses NII, ÑII( NII), and II(ÑII) are almost the general Petri nets except at least one MSTR(minimal structural trap) and at least one pair of "a virtual MSTR or a virtual STR" and "a virtual MSDL" of an MBTR (minimal behavioral trap) in connection with making an MSDL transition-live.

Until now, in a communication system which deals with multiple processes, system behavior has been described by a fixed number of processes. The state reachability problem for specified processes was generally deliberated within a pre-defined number of processes, and was analyzed by essentially searching for all possible behaviors. However, in a system whose number of processes is arbitrary, a given state which is not reachable in some situations which consists of a small number of processes might be reachable in another situation which consists of a larger number of processes. This article discusses the above problem, assuming that the behavior of a system is described by an arbitrary number of processes. After discussing the relationship between our model and the Petri net model, we clarify the properties between the set of reachable states and the number of processes involved in the system, and show an algorithm to obtain a sufficient number of processes for resolving the reachability problem.

We often use data flow diagrams or state transition diagrams to design software systems with concurrency. We call those diagrams as nets in this paper. Semantics of any methods to describe such software systems should be defined in some formal ways. There would be no doubts that any nets should be supported by appropriate theoretical frameworks. In this paper, we use CCS as a typical algebraic approach of using formulas to express concurrent behaviors and point out the different features of CCS from Petri nets. Any approaches should be not only theoretically beautiful but also practically useful. We use a specification language LOTOS as such example which has two features, CCS and ADT, and is designed to specify practical communication protocols. Algebraic approaches of using formulas, like LOTOS, can be considered as a compact way to express concurrent behaviors. We explore our discussions of net-oriented approaches into UIMS research fields. After mentioning state transition models of UIMS, we exemplify a practically used example, VIA-UIMS, which has been developed by one of authors. VIA-UIMS employs a net-oriented architecture. It has been designed to reconstuct tools which have already been widely used in many sites.

In this paper, we show that Petri nets can be applied practically to design and analysis of concurrent, parallel and embedded mode systems such as a lift system that is familiar to our daily life. Modeling behavioral characteristics of the lift, we extend a standard Petri net by constant timed transition, faultable transition, stochastic transition and condition transition concepts. Likewise, we prsesnt some results of design and analysis of the system. This method can be applied to design and analysis of another concurrent systems.

This article discusses on PDM (Petri net based Development Methodology) which integrates approaches, modeling methods, design methods and analysis methods in a coherent manner. Although various development techniques based on Petri nets have demonstrated advantages over conventional techniques, those techniques are rather ad hoc and lack an overall picture on entire development process. PDM anticipates to provide a refernce process model to develop distributed systems with various Petri net based development methods. Behavioral properties of distrbuted systems can be an appropriate application domain of PDM.

We describe K-NET, a support system for development of sequence control programs. The K-NET description model is based on the colored Petri net and timed Petri net. K-NET concisely expresses sequence control flow including synchronization, interlock and concurrence, and provides high-level data processing by being combined with a conventional procedural language. K-NET has an editor, simulator, generator, reporter and monitor to support the control program development procedure ranging from basic and detail design to programming and testing. We have added a new function to K-NET so it assists development of control programs for programmable controllers, and have applied it to an automatic bolt supplying system. The operation results are satisfactory.

The generation mechanism for excess intensity noise due to optical feedback is analyzed theoretically and experimentally. Modal rate equations under the weakly coupled condition with external feedback are derived to include the mode competition phenomena in DFB and Fabry-Perot lasers. We found that the sensitivity of the external feedback strongly depends on design parameters of structure, such as the coupling constant of the corrugation, the facet reflection and the phase relation between the corrugation and the facet. A DFB laser whose oscillating wavelength is well adjusted to Bragg wavelength through insertion of a phase adjustment region becomes less sensitive to external optical feedback than a Fabry-Perot laser, but other types of DFB lasers revealing a stop band are more sensitive than the Fabry-Perot laser.

In this paper, we propose a fuzzy Petri net model for a rule-based decision making system which contains uncertain conditions and vague rules. Using the transformation method introduced in the paper, one can obtain the fuzzy Petri net of the rule-based system. Since the fuzzy Petri net can be represented by some matrices, the algebraic form of a state equation of the fuzzy Petri net is systematically derived. Both forward and backward reasoning are performed by using the state equations. Since the proposed reasoning methods require only simple arithmetic operations under a parallel rule firing scheme, it is possible to perform real-time decision making with applications to control systems and diagnostic systems. The methodology presented is also applicable to classical (nonfuzzy) knowledge base systems if the nonfuzzy system is considered as a special case of a fuzzy system with truth values being equal to the extreme values only. Finally, an illustrative example of a rule-based decision making system is given for automobile engine diagnosis.

The self-organization rule of planar neural networks has been proposed for learning of 2D distributions. However, it cannot be applied to 3D objects. In this paper, we propose a new model for global representation of the 3D objects. Based on this model, global topology reserving self-organization is achieved using parallel local competitive learning rule such as Kohonen's maps. The proposed model is able to represent the objects distributively and easily accommodate local features.

Periodic schedules are seldom treated in the theory but abound in practice (air flight schedule, train schedule, manufacturing schedule, etc). This paper introduces a Petri Net based perspective to periodic schedules. These are classified, according to the time interpretation into single-server and multiple-server semantics and, according to transitions firing periodicity constraints, into strict and general periodic schedules. Using a net transformation rule, the computation of the general schedule class can be done through techniques for the strict subclass. Introducing truncation error terms ε for the floor functions, a necessary and sufficient condition for the feasibility of a strict periodic schedule is given in terms of a large size system of nonlinear inequalities containing ε terms. Moreover averaging this condition on subperiods allows to get a small size linear system of inequalities as necessary conditions for speeding up iterative computation processes. This paper aims to present qualitative analysis of periodic schedules for deterministically timed Petri net systems, as a precursor to quantitative analysis that requires large-scale computational experiments and hence will be dealt in later work.

This paper focuses on methodology underlying the application to fault tolerant computer systems with "no down communication" capability of stochastic Petri nets with general firing times. Based on a formal specification of the stochastic Petri net, we provide criteria for the marking process to be a regenerative process in continuous time with finite cycle-length moments. These results lead to strongly consistent point estimates and asymptotic confidence intervals for limiting system availability indices. We also show how the building blocks of stochastic Petri nets with general firing times facilitate the modeling of non-deterministic transition firing and illustrate the use of "interrupter input places" for graphical representation of transition interruptions.

Free choice nets are a class of Petri nets, which can represent the substantial features of systems by modeling both choice and concurrency. And in the modelling and design of a large number of concurrent systems, live and safe free choice nets (LSFC nets) have been explored their structural characteristics. On the other hand, state machine decomposable nets (SMD nets) are a class of Petri nets which can be decomposed by a set of strongly connected state machines (S-decomposition). State machine allocatable nets (SMA nets) are a well-behaved class of SMD nets. Of particular interest is the relation between free choice nets and SMA nets such that a free choice net has a live and safe marking if and only if the net is an SMA net. That is, the structure of an LSFC net is an SMA net. Recently, the structure of SMA net has been completely characterized by the authors based on an S-decomposition. In other words, a necessary and sufficient condition for a net to be an SMA net is obtained in terms of the net structure where synchronization between strongly connected state machine components (S-components) has been clarified. Unfortunately, it requires tremendous amount of time and spaces to decide a given net to be an SMA net by applying the condition directly. Moreover, there exist no efficient algorithm to decide the liveness and safeness of a given SMA net that lessens the usefulness of decomposition techniques. In this paper, we consider efficient polynomial order algorithms to decide whether a given net is a live and safe SHA net.

Marc Kellner proposed an example problem intending to compare modeling and describing techniques of software process. In this paper, we will describe our approach to understanding and describing the problem, from a process/product relation view, and synchronization/concurrent view. Also, we will show that a description of the problem is translated for execution and its correctness is validated.

This paper describes a programming system, K-NET for the development of control software for flexible manufacturing systems composed of robots, numerically-controlled machines, transfer machines and automatic storage/retrieval systems. K-NET is based on a high-level Petri net which makes it simple to express operational functions such as synchronization, interlock and concurrence in sequence control. Petri net in K-NET is colored one in which tokens have attributes, and timed one which can provide a notion of stochastic time. K-NET provides many kinds of boxes having specific functions, and gates specified the firing condition and the token flow control with IF-THEN rules. On the other hand, procedural language can be also used for information processing. K-NET can support all development stages including general design, detailed design, programming and testing. K-NET has an editor to input control specifications expressed with Petri net; a simulator to verify edited specifications; a generator to convert the net to C source programs for a computer or to ladder diagrams for a programmable controller; a reporter to print control specifications; and a monitor to display controller status in real-time. K-NET has been used in the development of control software for an automated guided vehicle system, and results show a 2/3rds cost-saving over development with conventional methods in which only procedural language is used.

This paper describes MENDELS ZONE, a Petri-net-based concurrent programming environment, which is especially suitable for cooperating discrete event systems. MENDELS ZONE adopts MENDEL net, which is a type of high level (hierarchical colored) Petri net. One of the characteristics of the MENDEL nets is a process-oriented hierarchy like CCS, which is different from the subnet-oriented hierarchy in the Jensen's hierarchical colored Petri net. In a process-oriented hierarchy, a hierarchical unit is a process, which is more natural for cooperating and decentralized discrete event control systems. This paper also proposes a design methodology for MENDEL nets. Although many Petri net tools have been proposed, most tools support only drawing, simulation, and analysis of Petri nets; few tools support the design methodology for Petri nets. While Petri nets are good final design documents easy to understand, analyzable, and executable it is often difficult to write Petri nets directly in an earlier design phase when the system structure is obscure. A proposed design methodology makes a designer to construct MENDEL nets systematically using causality matrices and temporal logic. Furthemore, constructed MENDEL nets can be automatically compiled into a concurrent programming language and executed on a parallel computer.

A job shop system typically seen in flexible manufacturing systems (FMS) is a system composed of a set of machines and a various kind of jobs processed with the machines. A production system of semiconductor fabrication is an example of job shop systems, which has main features of repetitive processes of one part and set-up times required for machines processing different types of parts. On the other hand, timed Petri nets are used for modelling and analyzing a wide variety of discrete event systems. There are many applications of timed Petri nets to the scheduling problems of job shop systems. The performance evaluation and steady state behaviors are studied by using the maximum cycle time of timed marked graphs. The aim of this paper is to propose a new model for production systems including repetitive processes and set-up time requirements which enables the quantitative analysis of real time system performance. In job shop systems such as a semiconductor fabrication system, it takes considerable amount of set-up time to prepare different types of chemical reactions and the model should take account of a set-up time for each machine. We focus upon the relationship between facility utilization factor and production cycle time in the steady state. In the proposed model, the minimum total set-up time can be attained. Quantitative relationship between utilization factor and production cycle time is derived by using the proposed model. A utilization factor of a system satisfying a given limit of the cycle time is evaluated, and the improvement of the utilization factor is considered. Conversely, we consider the improvement of the cycle time of a system satisfying a given limit of utilization factor.

The subject of the paper is the minimum initial marking problem for scheduling in timed Petri net PN: given a vector X of nonnegative integers, a P-invariant Y of PN and a nonnegative integer π, find an initial marking M minimizing the value YtrM among those initial marking M such that there is a scheduling σ having the total completion time τ(σ)π with respect M , X and PN (a sequence of transitions, with the first transition firable on M , such that every transition t can fire prescribed number X(t) of times). The paper shows NP-hardness of the problem and proposes two approximation algorithms with their experimental evaluation.

Recent trends in down-sizing have resulted in the development of client server systems for many industries. This paper considers the application of stochastic Petri nets with general firing times for modeling of a concatenated client server system and the use of discrete-event simulation methods for stochastic Petri nets to study its behavior. This approach enables us to assess the most appropriate resource set of a concatenated client server system on the quantitative basis of the performability and the occurrence of system down conditions. Thus, system consultation, a new application of stochastic Petri nets, is presented.

The pursuit of higher availability has resulted in the development of fault tolerant systems for many industries. However, system characteristics that can be perceived by the customer have never been diagnosed quantitatively. This paper considers the application of stochastic Petri nets with general firing times to modeling of a fault tolerant system and the use of discrete-event simulation methods for stochastic Petri nets to study the behavior of the system. The stochastic Petri net model incorporates factors that compose the system as well as those that accompany it, including RAS characteristics of products, personnel arrangements, and system management. By modeling the behavioral aspect of each factor, it is possible to diagnose a fault tolerant system quantitatively on the basis of customer impact.