Machine Learning is the study of methods for programming computers to learn. Computers are applied to a wide range of tasks, and for most of these it is relatively easy for programmers to design and implement the necessary software. However, there are many tasks for which this is difficult or impossible. These can be divided into four general categories. First, there are problems for which there exist no human experts. For example, in modern automated manufacturing facilities, there is a need to predict machine failures before they occur by analyzing sensor readings. Because the machines are new, there are no human experts who can be interviewed by a programmer to provide the knowledge necessary to build a computer system. A machine learning system can study recorded data and subsequent machine failures and learn prediction rules. Second, there are problems where human experts exist, but where they are unable to explain their expertise. This is the case in many perceptual tasks, such as speech recognition, hand-writing recognition, and natural language understanding. Virtually all humans exhibit expert-level abilities on these tasks, but none of them can describe the detailed steps that they follow as they perform them. Fortunately, humans can provide machines with examples of the inputs and correct outputs for these tasks, so machine learning algorithms can learn to map the inputs to the outputs. Third, there are problems where phenomena are changing rapidly. In finance, for example, people would like to predict the future behavior of the stock market, of consumer purchases, or of exchange rates. These behaviors change frequently, so that even if a programmer could construct a good predictive computer program, it would need to be rewritten frequently. A learning program can relieve the programmer of this burden by constantly modifying and tuning a set of learned prediction rules. Fourth, there are applications that need to be customized for each computer user separately. Consider, for example, a program to filter unwanted electronic mail messages. Different users will need different filters. It is unreasonable to expect each user to program his or her own rules, and it is infeasible to provide every user with a software engineer to keep the rules up-to-date. A machine learning system can learn which mail messages the user rejects and maintain the filtering rules automatically. Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis. Statistics focuses on understanding the phenomena that have generated the data, often with the goal of testing different hypotheses about those phenomena. Data mining seeks to find patterns in the data that are understandable by people. Psychological studies of human learning aspire to understand the mechanisms underlying the various learning behaviors exhibited by people (concept learning, skill acquisition, strategy change, etc.).

Machine learning

ing WS1S Systems to Verify Parameterized Networks . . . . . . . . . . . . 188 Kai Baukus, Saddek Bensalem, Yassine Lakhnech and Karsten Stahl FMona: A Tool for Expressing Validation Techniques over Infinite State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 J.-P. Bodeveix and M. Filali Transitive Closures of Regular Relations for Verifying Infinite-State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 Bengt Jonsson and Marcus Nilsson Diagnostic and Test Generation Using Static Analysis to Improve Automatic Test Generation . . . . . . . . . . . . . 235 Marius Bozga, Jean-Claude Fernandez and Lucian Ghirvu Efficient Diagnostic Generation for Boolean Equation Systems . . . . . . . . . . . . 251 Radu Mateescu Efficient Model-Checking Compositional State Space Generation with Partial Order Reductions for Asynchronous Communicating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Jean-Pierre Krimm and Laurent Mounier Checking for CFFD-Preorder with Tester Processes . . . . . . . . . . . . . . . . . . . . . . . 283 Juhana Helovuo and Antti Valmari Fair Bisimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Thomas A. Henzinger and Sriram K. Rajamani Integrating Low Level Symmetries into Reachability Analysis . . . . . . . . . . . . . 315 Karsten Schmidt Model-Checking Tools Model Checking Support for the ASM High-Level Language . . . . . . . . . . . . . . 331 Giuseppe Del Castillo and Kirsten Winter Table of

Tools and Algorithms for the Construction and Analysis of Systems. Proc. TACAS 2009

Technical report series

Handbook of logic in computer science.

The π-Calculus: A theory of mobile processes by Davide Sangiorgi and David Walker Formal methods have formed the foundation of Computer Science since its inception. Although, initially these formal methods dealt with processes and systems on an individual basis, the paradigm has shifted with the dawn of the age of computer networks. When dealing with systems with interconnected, communicating, dependent, cooperative, and competitive components, the older outlook of analyzing and developing singular systems—and the tools that went with it—were hardly suitable. This led to the development of theories and tools that would support the new paradigm. On the tools end, the development has been widespread and satisfactory: programming languages, development frameworks, databases, and even end-user software products such as word processors, have gained network-awareness. However on the theoretical end, the development has been far less satisfactory. The major work was done by Robin Milner, Joachim Parrow, and David Walker who developed the formalism known as π-calculus in 1989. π-calculus is a process calculus that treats communication between its components as the basic form of computation. It has been quite successful as a foundation of several other calculi in the field and as Milner puts it, it has become common to express ideas about interactions and mobility in variants of the calculus. Introduction The current book serves as a comprehensive reference to π-calculus. Besides Milner's own book on the subject, this is the only other book-length publication on the topic. In many ways, it is much more comprehensive than Milner's: a much wider area of topics are dealt with and in more detail as well. Contents The book is split into seven part. The first part presents the basic theory of π-calculus. However, basic does not mean concise: every topic is discussed in great detail. The section on bisimulation is particularly intensive and provides several insights about the motivation for the theory. Part two discusses several variants of the original calculus. By varying several characteristics of the calculus, such as whether a process can communicate with more than processes at a time, we can obtain these variants. A number of interesting properties of the language are studied by the other when discussing these variants. As can be understood from the title, the calculus' contribution to analyzing mobile processes is a major topic, and it is dealt with extensively starting from part three. The basics are introduced by the way of a sophisticated typing system whose application in speciying complex processes is presented in part four. Part five looks at higher-order π-calculus in which composed systems are considered as first-class citizens. Part six is one of the best in the book and discusses the relation between π-calculus and lambda-calculus, which is an older and more basic calculus. Finally part seven shows how π-calculus can be employed in studying practical, modern software engineering concepts such as object-oriented programming. Impressions One of my disappointments with this book is in how often the reader is left perplexed with some of the theoretical developments, specially in part three. π-calculus is a complicated topic, even for the graduate student audience to which this book is directed, and the author would have done much better by reducing the number of topics and instead focusing on more lucid and detailed explanations. There are several experimental digressions throughout the book, which although interesting, take away from some of the momentum of sequential study. For example, topics such as comparison and encoding of one language to another could be easily moved to a separate section in order to make the content more suitable for self-study. Another issue is the little effort towards making the connection from the theoretical to the practical. The main reason why formal methods have not been adopted in mainstream software development pracitces is that often it is unclear to developers how formalisms can contribute towards the software engineering process. The book would have served its purpose much better if it had spent part of eah chapter discussing the practical application of that chapter's content. For example, congruence checking and bisimulation can be incredbily exciting topics for programmers to learn if they can see practical applications of such powerful techniques. Beyond the above criticism, the book is absolutely indispensible to students and researchers in the field of formal methods. Currently it serves as the primary reference for anyone who wishes to learn the various aspects of π-calculus in detail. Raheel Ahmad

The Ï-Calculus: A theory of mobile processes

Various execution semantics of concurrent systems are formally defined and investigated. The problem of the existence of minimal execution semantics equivalent to the semantics expressed intuitively as “execute as possible” is studied. The positive answer to that problem is given.

On Equivalent Execution Semantics of Concurrent Systems

In this paper, we further develop a recently introduced semantic link between temporal logics and Petri nets. We focus on two specific formalisms, Interval Temporal Logic (ITL) and Box Algebra (BA), which are closely related by their compositional approach to constructing system descriptions. The overall goal of our investigation is to translate Petri nets into behaviourally equivalent logical formulas. As a result, the analysis of system properties can be carried out using either of the two formalisms, exploiting their respective strengths and powerful tool support. The contribution of this paper is twofold. First, we extend the existing translation from BA to ITL, by removing restrictions concerning the way control flow of concurrent system is modelled, and by allowing a fully general synchronisation operator. Second, we strengthen the notion of equivalence between a Petri net and the corresponding logical formula by proving such an equivalence at the level of transition-based executions of Petri nets rather than just by looking at their labels. We also show that the complexity of the proposed translation compares favourably with the complexity of the translation from BA expressions to Petri nets.

/pdf/from-box-algebra-to-interval-temporal-logic-56zpgkfnzf.pdf

From Box Algebra to Interval Temporal Logic

A step alphabet describes dependencies between the actions of a concurrent system in the form of two relations expressing potential simultaneity and sequentialisability. These form the basis for the identification of step sequences as observations of the same run of the system. The resulting equivalence classes – step traces – can be represented by (labelled) invariant structures with two relations, viz. mutex and weak causality. In this paper, we address the following synthesis problem for acyclic invariant structures which are structures corresponding to step traces with sequential realisations: given an acyclic invariant structure that can represent a step trace, construct a suitable step alphabet, i.e., provide suitable simultaneity and sequentialisability relations for its actions. The main result is that the set of all suitable alphabets forms a complete lattice with the ordering derived from the relative ‘strength’ of the dependencies between individual actions.

/pdf/on-synthesising-step-alphabets-for-acyclic-invariant-ptq53j5tje.pdf

On Synthesising Step Alphabets for Acyclic Invariant Structures

It is often desirable to describe the interface of an implementation system at a different (usually more detailed) level of abstraction to the interface of the relevant specification. This calls for a relation aimed at formalising the notion that a process is an acceptable implementation of another target process in the event that they possess different interfaces. This paper formulates a suitable implementation relation between the observable behaviours of the implementation and the target process using CSP. Interface difference and bridging is modelled by endowing the implementation relation with parameters, called extraction patterns, instrumental to interpreting implementation behaviour as target behaviour. It is often desirable to describe the interface of an implementation system at a different (usually more detailed) level of abstraction to the interface of the relevant specification. This calls for a relation aimed at formalising the notion that a process is an acceptable implementation of another target process in the event that they possess different interfaces. This paper formulates a suitable implementation relation between the observable behaviours of the implementation and the target process using CSP. Interface difference and bridging is modelled by endowing the implementation relation with parameters, called extraction patterns, instrumental to interpreting implementation behaviour as target behaviour. It is often desirable to describe the interface of an implementation system at a different (usually more detailed) level of abstraction to the interface of the relevant specification. This calls for a relation aimed at formalising the notion that a process is an acceptable implementation of another target process in the event that they possess different interfaces. This paper formulates a suitable implementation relation between the observable behaviours of the implementation and the target process using CSP. Interface difference and bridging is modelled by endowing the implementation relation with parameters, called extraction patterns, instrumental to interpreting implementation behaviour as target behaviour.

Towards an Algebra of Abstractions for Communicating Processes

Model checking based on the causal partial order semantics of Petri nets is an approach widely applied to cope with the state space explosion problem. One of the ways to exploit such a semantics is to consider (finite prefixes of) net unfoldings — themselves a class of acyclic Petri nets — which contain enough information, albeit implicit, to reason about the reachable markings of the original Petri nets. In [15], a verification technique for net unfoldings was proposed in which deadlock detection was reduced to a mixed integer linear programming problem. In this paper, we present a further development of this approach. We adopt Contejean-Devie’s algorithm for solving systems of linear constraints over the natural numbers domain and refine it, by taking advantage of the specific properties of systems of linear constraints to be solved. The essence of the proposed modifications is to transfer the information about causality and conflicts between the events involved in an unfolding, into a relationship between the corresponding integer variables in the system of linear constraints. Experimental results demonstrate that the new technique achieves significant speedups.

Maciej Koutny

Papers

On Equivalent Execution Semantics of Concurrent Systems

From Box Algebra to Interval Temporal Logic

On Synthesising Step Alphabets for Acyclic Invariant Structures

Towards an Algebra of Abstractions for Communicating Processes

Linear Programming Deadlock Checking Using Partial Order Dependencies