Optimal Legal Firing Sequence of Petri Nets Using Linear Programming

Petri nets (PNs) are a reliable graphical and mathematical modeling tool for the formal modeling and validation of systems (W. Reisig, A Primer in Petri Net Design, Springer-Verlag: Berlin, Heidelberg, 1992). Applications of PNs include discrete event dynamic systems (DEDS) that are recognized as being concurrent, asynchronous, distributed, parallel, and/or nondeterministic. It is also a powerful formal method for the analysis of concurrent, embedded, and distributed finite state systems (K. Varpaaniemi, Series A: Research Reports, No. 26, Helsinki University of Technology, Digital Systems Laboratory, Oct. 1993). The reachability analysis of PNs is strategically significant as it captures the dynamic behavior of the system as well as providing efficient verification of the correctness of the model. Few linear programming (LP)-based methods can be found that address the reachability problem, and some of these are suitable for optimal control problems. However, due to an inherent state explosion they are difficult to implement; other methods run easily into deadlock as they lack appropriate mechanisms to avoid the firing of critical transitions (T. Matsumoto and A. Tarek, in Proceedings of the 35th IEEE Conference on Decision and Control, Kobe, Japan, 1996-12, pp. 4459–4468). In this paper an improved and easy to implement method is proposed that combines the Optimality Principle and Linear Programming (OP + LP) techniques to find an Optimal Legal Firing Sequence (OLFS) in PNs. This method can be applied to ordinary PNs with self-loops, avoids deadlocks, and can also be used for general PNs having cycles.     

Modelling global computations with KLAIM

A new area of research, known as Global Computing, is by now well established. It aims at defining new models of computation based on code and data mobility over wide-area networks with highly dynamic topologies, and at providing infrastructures to support coordination and control of components originating from different, possibly untrusted, fault-prone, malicious or selfish sources. In this paper, we present our contribution to the field of Global Computing that is centred on Kernel Language for Agents Interaction and Mobility (Klaim ). Klaim is an experimental language specifically designed to programme distributed systems consisting of several mobile components that interact through multiple distributed tuple spaces. We present some of the key notions of the language and discuss how its formal semantics can be exploited to reason about qualitative and quantitative aspects of the specified systems.     

Synthesis of FBD-based PLC design from NuSCR formal specification

NuSCR is a formal specification language to document requirements for real-time embedded software with nuclear engineering applications in mind. Domain experts actively participated in selecting how to best represent various aspects. It uses tabular notations to specify required computations and automata to document state- or time-dependent behavior. As programmable logic controllers (PLCs) are widely used to implement real-time embedded software, synthesis of PLC code from a formal specification is desirable if transformation rules can be rigorously defined. In addition to improved productivity, results of safety analysis performed on requirements remain valid. In this paper, we demonstrate how NuSCR specification can be translated into semantically equivalent function block diagram (FBD) code. The process, except the initial phase where user provides information on missing or implicit details, is automated. Since executable code can be automatically generated using CASE tools from FBD, much of software development is automated. Proposed technique is currently being used in developing reactor protection system (RPS) for nuclear power plants in Korea, and experience to date has been positive. We demonstrate the proposed approach using the fixed set-point rising trip which is one of the most complex trip logics included in the RPS.     

An abductive propositional logic for design reasoning

Abstract

Design can be seen as a reasoning process based on non‐classic logic, in which non‐monotonicity and abduction are two essential features. This paper introduces Abductive Propositional Logic (APL), which is a simple but powerful formal system to deal with these two features. To show its capabilities, APL is used to analyze the reasoning of a conceptual design of a scooter. The results reveal that APL is not only a profound basis for developing computer supported design systems, but also a useful tool for analyzing design processes.     

Logic programming to predict cell fate patterns and retrodict genotypes in organogenesis

Caenorhabditis elegans vulval development is a paradigm system for understanding cell differentiation in the process of organogenesis. Through temporal and spatial controls, the fate pattern of six cells is determined by the competition of the LET-23 and the Notch signalling pathways. Modelling cell fate determination in vulval development using state-based models, coupled with formal analysis techniques, has been established as a powerful approach in predicting the outcome of combinations of mutations. However, computing the outcomes of complex and highly concurrent models can become prohibitive. Here, we show how logic programs derived from state machines describing the differentiation of C. elegans vulval precursor cells can increase the speed of prediction by four orders of magnitude relative to previous approaches. Moreover, this increase in speed allows us to infer, or ‘retrodict’, compatible genomes from cell fate patterns. We exploit this technique to predict highly variable cell fate patterns resulting from dig-1 reduced-function mutations and let-23 mosaics. In addition to the new insights offered, we propose our technique as a platform for aiding the design and analysis of experimental data.     

Formal reasoning about synthetic biology using higher‐order‐logic theorem proving

Synthetic biology is an interdisciplinary field that uses well‐established engineering principles for performing the analysis of the biological systems, such as biological circuits, pathways, controllers and enzymes. Conventionally, the analysis of these biological systems is performed using paper‐and‐pencil proofs and computer simulation methods. However, these methods cannot ensure accurate results due to their inherent limitations. Higher‐order‐logic (HOL) theorem proving is proposed and used as a complementary approach for analysing linear biological systems, which is based on developing a mathematical model of the genetic circuits and the bio‐controllers used in synthetic biology based on HOL and analysing it using deductive reasoning in an interactive theorem prover. The involvement of the logic, mathematics and the deductive reasoning in this method ensures the accuracy of the analysis. It is proposed to model the continuous dynamics of the genetic circuits and their associated controllers using differential equations and perform their transfer function‐based analysis using the Laplace transform in a theorem prover. For illustration, the genetic circuits of activated and repressed expressions and autoactivation of protein, and phase lag and lead controllers, which are widely used in cancer‐cell identifiers and multi‐input receptors for precise disease detection, are formally analyzed.Inspec keywords: program verification, diseases, genetics, cancer, formal logic, theorem proving, formal verification, differential equations, proteins, transfer functions, inference mechanisms, Laplace transformsOther keywords: biological system, biological circuits, genetic circuits, associated controllers, computer simulation methods, higher‐order‐logic theorem proving, analysing linear biological systems, bio‐controllers, synthetic biology, deductive reasoning, reaction‐based models, transfer function based analysis, differential equation based models, phase lag, lead controllers, computer systems     

Strategy of Concurrent Optimization for an Assembly Sequence

An effective constraint release based approach to realize concurrent optimization for an assembly sequence is proposed. To quantify the measurement of assembly efficiency, a mathematical model of concurrency evaluation index was put forward at first, and then a technology to quantify assembly constraints was developed by application of some fuzzy logic algorithms. In the process of concurrent optimization of the assembly sequence, two kinds of constraints were involved. One was self-constraints of components, which was used to evaluate the assemble capability of components under the condition of full-freedom. Another was an assembly constraint between components represented by geometric constraints between points, lines and planes under physical restriction conditions. The concept of connection strength degree （CSD） was introduced as one efficient indicator and the value of it was evaluated by the intersection of the two constraints mentioned above. The equivalent constraints describing the connection weights between components were realized by a well designed constraints reduction, and then the connection weights based complete assembly liaison graph was applied to release virtual connections between components. Under a given threshold value, a decomposition and reconstituting strategy for the graph with the focus on high assembly concurrency was used to realize an optimized assembly concurrency evaluation index. Finally, the availability of the approach was illustrated in an example to optimize the assembly of a shift pump.     

一种面向事务型数据库的无锁并发B+tree索引结构

为了克服现有多版本并发控制(MVCC)进行数据的并发访问控制中短暂阻塞的缺点,达到读写完全并发,提出了一种基于写时复制的多版本并发B+tree(BCMVBT)索引结构。BCMVBT通过复制分离读写的操作空间以使读写事务在任意时刻完全并发执行,规避比较与交换(CAS)操作带来的高CPU消耗,达到一写多读场景下的完全并发。同时针对现有多版本开发B+tree(MVBT)范围查询的复杂操作,提出了无锁的BCMVBT的范围查询算法和回收机制,从而实现了索引的插入、查询、更新与回收的无锁并发操作。通过与事务型MVBT(transaction MVBT)的对比,在读写并发环境下BCMVBT的时间消耗降低了50%,实验进一步表明BCMVBT在大事务的场景下具有更高的优势。     

Performance-driven object-oriented program re-modularisation

The aim is to achieve the highest possible speedup when distributing a program across a cluster of computational nodes. The speedup may be achieved by concurrent execution of the distributed modules. In order to maximise the concurrency, a two-stage approach is proposed. In the first stage, a novel statement-reordering algorithm reorders the statements within a given program, to maximise the distance between each call instruction and the instructions, which are data-dependent on any value affected by the call. In the second stage, a clustering algorithm is applied to look for a modular structure of the program which results in the highest concurrency in its execution. The clustering algorithm applies a novel performance evaluation function which is derived from the program code, automatically.     

Noncollinear Ground States in Ferromagnetic (III,Mn)V Semiconductors

Disorder-induced noncollinear ferromagnetism is a common feature of kinetic-exchange models for ferromagnetic (III,Mn)V semiconductors with randomly distributed Mn ions. The instability of the collinear state is due to long-ranged fluctuations involving a large fraction of the localized magnetic moments. In cases were the true ground state magnetization is reduced substantially from the maximum value of the collinear state one finds a complex energy landsacpe with many metastable minima. Finally we report on studies of the influence of an external field realigning the Mn spins starting from a glassy zero-field ground state.     

Formal Approach to Workflow Application Fragmentations Over Cloud Deployment Models

Workflow management technologies have been dramatically improving their deployment architectures and systems along with the evolution and proliferation of cloud distributed computing environments. Especially, such cloud computing environments ought to be providing a suitable distributed computing paradigm to deploy very large-scale workflow processes and applications with scalable on-demand services. In this paper, we focus on the distribution paradigm and its deployment formalism for such very large-scale workflow applications being deployed and enacted across the multiple and heterogeneous cloud computing environments. We propose a formal approach to vertically as well as horizontally fragment very large-scale workflow processes and their applications and to deploy the workflow process and application fragments over three types of cloud deployment models and architectures. To concretize the formal approach, we firstly devise a series of operational situations fragmenting into cloud workflow process and application components and deploying onto three different types of cloud deployment models and architectures. These concrete approaches are called the deployment-driven fragmentation mechanism to be applied to such very large-scale workflow process and applications as an implementing component for cloud workflow management systems. Finally, we strongly believe that our approach with the fragmentation formalisms becomes a theoretical basis of designing and implementing very large-scale and maximally distributed workflow processes and applications to be deployed on cloud deployment models and architectural computing environments as well.     

Modelling real-time systems: Issues and challenges

In this paper, we discuss the issues and challenges that lie in the specification, development, and verification of real-time systems. In our presentation, we emphasize on the issues underlying modelling of real-time distributed concurrency. Partial support by the Indo-French Centre for the Promotion of Advanced Research/Centre Franco-Indien Pour la Promotion de la Recherche Advancee as part of the project “Formal Specification and Development of Real-Time Reactive Programs” is gratefully acknowledged.     

Process algebras as support for sustainable systems of services

Process algebras are indispensable tools in modeling concurrent processes in theoretical computer science. We propose a novel use of process algebra as a back-bone in designing and maintaining complex open distributed information systems. Our π-calculus approach allows us to create and maintain service based mission oriented tasks with intended behaviors and with support for observing and maintaining mission critical systemic criteria.     

Manufacturing supply chain modelling and reengineering

The first-wave of reengineering, during the first half of the nineties, focused on making organizational changes and used primarilyinformation models of supply chains to integrate business processes.Quantitative models are expected to have a significant impact in the second-wave of reengineering through the deployment of performance and optimization models, economic analysis, and decision support systems. In this paper, we focus on the vital role that quantitative modelling techniques such as those founded in Operations Research and Industrial Engineering can play in reengineering supply chains. These quantitative models can extend the business process reengineering concepts to provide a concurrent reengineering framework for modelling the supply chain processes, identifying reengineering opportunities, evaluating design alternatives, guiding the selection of the best alternative, and deploying tools to implement the design. We illustrate such use by surveying current industrial practice and introducing real world examples based on our practical experience in solving supply chain and reengineering problems.     

Post-Certification Engineering Taxonomy and Task Value Optimization in the Aerospace Industry

Abstract:

This article proposes a novel taxonomy of post-certification engineering activities as a first step toward true lean product development (PD). Relying on key notions developed in a novel lean engineering performance model, the authors compare the leanness of post-certification versus pre-certification tasks for the design of aerospace parts. Discrete event simulation and integer linear programming models are developed to help ascertain the influence of factors such as multitasking, concurrency, task size, task value, and post-certification budget decision making on lean engineering PD performance. The models developed provide the foundation for enhanced PD performance and the establishment of optimal PD process parameters.     

Extended structured adaptive supervisory control model of shop floor controls for an e-Manufacturing system

The high cost and long development cycle of shop floor control systems and the lack of true system integration capabilities are identified as one of the most challenging obstacles in deploying e-Manufacturing systems. Overcoming these obstacles is essential for manufacturers to execute a make-to-order business model in order to stay competitive and remain profitable in the future. We propose a formal method to generate the desired control trajectories and provide true integration mechanisms for shop floor control systems. Using the proposed architecture can result in the development of an e-Manufacturing system capable of achieving a substantial reduction of both the high cost and long development cycle currently required to engineer shop floor control systems. By taking advantage of both the linear growth of the complexity function in a structured adaptive supervisory control model and the information-centric characteristics of a virtual production line in a manufacturing execution system, a formal model, which we call an extended structured adaptive supervisory control, for a discrete manufacturing system is introduced. A shop floor control system based on the extended structured adaptive supervisory control model is built for an industrial testbed system. The shop floor control system is fully tested and evaluated.     

An incremental objective achievement model in computerized procedure execution

A procedure building block, called an objective in this paper, is developed by integrating decisions, actions, and responses to the actions. The objective is characterized as a success logic tree, which consists of 5 logic operators, Boolean checks, and actions. Operational rules of the objective are simple. Perform all available actions and checks until the success logic tree becomes true, if not specified differently. The objective has formality and the characteristics of the state-function, which make verification and validation, situation awareness, and the controls of a plant enhanced. The specification of the objective is described by a top–down approach and illustrated with examples. The goal of a procedure is achieved through executions of successive objectives. Translation from paper procedures, printout, and maintenance are also improved. A sample man–machine interface and interaction based on this model is suggested.     

Critical scenarios derivation methodology for mechatronic systems

This paper deals with safety in design of mechatronic systems. We propose a method based on a qualitative analysis of a Petri net model of the system. It allows deriving feared scenarios by determining the sequences of actions and state changes leading to the feared state in which the passenger's safety is no longer guaranteed. The Petri net model of the system takes into account normal behaviour, failures and reconfiguration mechanisms. Our approach uses linear logic as formal framework and is based on a backward and a forward reasoning. It derives feared scenarios as causal relationships between normal states and the feared one.     

Towards automated verification of layered graph transformation specifications

Graph transformation systems have recently become more and more popular as a general formal modelling language. It is a suitable formalism for modelling different systems like distributed and complex systems. However, modelling must be complemented with proper analysis capabilities to let the user understand how designed models behave and whether stated requirements are fulfilled and model checking has proven to be a viable solution for this purpose. The authors propose an efficient solution for model checking attributed typed and layered graph transformation systems. Layered graph transformation systems are a powerful formalism to formally model different systems like hierarchical systems. In our proposal, AGG layered graph transformation specifications are translated to Bandera intermediate representation (BIR) - the input language of a Bogor model checker - and then Bogor verifies the model against some interesting properties defined by combining LTL (linear temporal logic) and special graph rules. The experimental results are encouraging and show that in most cases our proposal improves existing approaches, in terms of both performance and expressiveness.     

Maintenance optimisation from a decision theoretical point of view

Maintenance optimisation is rarely discussed from a decision theoretical point of view. It is believed that maintenance programmes may benefit from using decision theory in a more formal manner. In decision theory there is a sharp line of demarcation between establishing requirements and preferences on one side, and methods for seeking an optimal solution in accordance with the requirements and preferences on the other side. We discuss requirements and preferences concerning maintenance, and how to model these by value and utility functions. Next we discuss how to choose the optimum set of maintenance actions. Influence diagrams are introduced to visualise the relation between maintenance actions, system characteristics and value functions. Finally an illustrative example is given.