David Harel – författare

Computers are incredible. They are one of the most important inventions of the 20th century, dramatically and irrevocably changing the way we live. That is the good news. The bad news is that there are still major limitations to computers, serious problems that not even the most powerful computers can solve. The consequences of such limitations can be serious. Too often these limits get overlooked, in the quest for bigger, better, and more powerful computers. In Computers Ltd., David Harel, best-selling author of Algorithmics, explains and illustrates one of the most fundamental, yet under-exposed facets of computers - their inherent limitations. Looking at the bad news that is proven, lasting and robust, discussing limitations that no amounts of hardware, software, talents or resources can overcome, the book presents a disturbing and provocative view of computing at the start of the 21st century. Along the way he shows just how far from perfect computers are, while shattering some of the many claims made for these machines. Though we may strive for bigger and better things in computing, we need to be realistic: computers are not omnipotent - far from it.Moreover, the problem is real and here to stay.

The best selling 'Algorithmics' presents the most important, concepts, methods and results that are fundamental to the science of computing.  It starts by introducing the basic ideas of algorithms, including their structures and methods of data manipulation.  It then goes on to demonstrate how to design accurate and efficient algorithms, and discusses their inherent limitations.  As the author himself says in the preface to the book; 'This book attempts to present a readable account of some of the most important and basic topics of computer science, stressing the fundamental and robust nature of the science in a form that is virtually independent of the details of specific computers, languages and formalisms'.

Software engineering has over the years been applied in many different fields, ranging from telecommunications to embedded systems in car and aircraft industry as well as in production engineering and computer networks. Foundations in software technology lie in models allowing to capture application domains, detailed requirements, but also to understand the structure and working of software systems like software architectures and programs. These models have to be expressed in techniques based on discrete mathematics, algebra and logics. However, according to the very specific needs in applications of software technology, formal methods have to serve the needs and the quality of advanced software engineering methods, especially taking into account security aspects in Information Technology. This book presents mathematical foundations of software engineering and state-of-the-art engineering methods in their theoretical substance in the step towards practical applications to examine software engineering techniques and foundations used for industrial tasks.The contributions in this volume emerged from lectures of the 25th International Summer School on Engineering Theories of Software Intensive Systems, held at Marktoberdorf, Germany from August 3 to August 15, 2004.

Software engineering has over the years been applied in many different fields, ranging from telecommunications to embedded systems in car and aircraft industry as well as in production engineering and computer networks. Foundations in software technology lie in models allowing to capture application domains, detailed requirements, but also to understand the structure and working of software systems like software architectures and programs. These models have to be expressed in techniques based on discrete mathematics, algebra and logics. However, according to the very specific needs in applications of software technology, formal methods have to serve the needs and the quality of advanced software engineering methods, especially taking into account security aspects in Information Technology. This book presents mathematical foundations of software engineering and state-of-the-art engineering methods in their theoretical substance in the step towards practical applications to examine software engineering techniques and foundations used for industrial tasks.The contributions in this volume emerged from lectures of the 25th International Summer School on Engineering Theories of Software Intensive Systems, held at Marktoberdorf, Germany from August 3 to August 15, 2004.

This book presents a powerful new language and methodology for programming complex reactive systems in a scenario-based manner. The language is live sequence charts (LSCs), a multimodal extension of sequence charts and UML's sequence diagrams, used in the past mainly for requirements. The methodology is play-in/play-out, an unusually convenient means for specifying inter-object scenario-based behavior directly from a GUI or an object model diagram, with the surprising ability to execute that behavior, or those requirements, directly. The language and methodology are supported by a fully implemented tool - the Play-Engine - which is attached to the book in CD form. Comments from experts in the field:The design of reactive systems is one of the most challenging problems in computer science. This books starts with a critical insight to explain the difficulty of this problem: there is a fundamental gap between the scenario-based way in which people think about such systems and the state-based way in which these systems are implemented. The book then offers a radical proposal to bridge this gap by means of playing scenarios.Systems can be specified by playing in scenarios and implemented by means of a Play-Engine that plays out scenarios. This idea is carried out and developed, lucidly, formally and playfully, to its fullest. The result is a compelling proposal, accompanied by a prototype software engine, for reactive systems design, which is bound to cause a splash in the software-engineering community. Moshe Y. Vardi, Rice University, Houston, Texas, USAScenarios are a primary exchange tool in explaining system behavior to others, but their limited expressive power never made them able to fully describe systems, thus limiting their use. The language of Live Sequence Charts (LSCs) presented in this beautifully written book achieves this goal, and the attached Play-Engine software makes these LSCs really come alive. This is undoubtedly a key breakthrough that will start long-awaited and exciting new directions in systems specification, synthesis, and analysis. Gerard Berry, Esterel Technologies and INRIA, Sophia-Antipolis, FranceThe approach of David Harel and Rami Marelly is a fascinating way of combining prototyping techniques with techniques for identifying behavior and user interfaces.Manfred Broy, Technical University of Munich, Germany

Algorithmen sind der Kern der Informatik und der Mathematik, da jede Nutzung eines Computers erst durch Rechenverfahren überhaupt möglich wird. In diesem Buch, das in der englischen Originalausgabe schon lange ein Bestseller ist, gibt der Autor und sein Co-Autor umfassend und didaktisch geschickt Auskunft zu allen Fragen rund um das Thema Algorithmen, so z.B. zu Themen wie Berechenbarkeit, Korrektheit und Effizienz von Algorithmen, zu Programmiertechniken, und auch das aktuelle Thema Quantenrechnen wird behandelt. Das Buch kann als Grundlage eines einsemestrigen Einführungskurses in die Informatik dienen, oder als allgemeine Informatik-Einführung in den Naturwissenschaften, der Mathematik oder im Ingenieurwesen.

Können Computer alles? Wenn es so wäre, gäbe es dieses Buch nicht. Es beweist bestechend logisch, dass selbst die größten, schnellsten, intelligentesten und teuersten Computer der Welt nur beschränkt leistungsfähig sind. Der Mensch kann noch so viel Geld, Zeit und Know-how investieren, es gibt Computer-Probleme, die er niemals lösen wird. Eine beunruhigende, provokative Botschaft - und doch: wussten wir es nicht eigentlich schon, haben es aber nie wirklich glauben wollen? Der bekannte Computer-Wissenschaftler David Harel vermittelt die mathematischen Fakten spannend, unterhaltsam und allgemeinverständlich. Mit der Beschränktheit des Computers werden wir an die Grenzen allen Wissens geführt. Grenzen, die den Menschen beflügeln, das Mögliche weiter zu verbessern und selbst aus dem Unmöglichen Nutzen zu ziehen. Eine brillante tour de force mit überraschenden Aspekten, die den Leser - ob vorgebildeter Laie oder Fachkundiger - von der ersten bis zur letzten Seite fesselt.

This book constitutes the refereed proceedings of the 9th International Conference on Model Driven Engineering Languages and Systems (formerly the UML series of conferences), MoDELS 2006, held in Genova, Italy, in October 2006. The 51 revised full papers and 2 invited papers presented were carefully reviewed and selected from 178 initial submissions. The papers are organized in topical sections on evaluating UML, MDA in software development, concrete syntax, applying UML to interaction and coordination, aspects, model integration, formal semantics of UML, security, model transformation tools and implementation, analyzing dynamic models, specifying transformations, MOF, bridging models, risk, trust and dependability, tool environments, OCL, roundtrip engineering, real time and embedded systems, as well as workshops, tutorials and panels.

A fundamental understanding of algorithmic bioprocesses is key to learning how information processing occurs in nature at the cell level. The field is concerned with the interactions between computer science on the one hand and biology, chemistry, and DNA-oriented nanoscience on the other. In particular, this book offers a comprehensive overview of research into algorithmic self-assembly, RNA folding, the algorithmic foundations for biochemical reactions, and the algorithmic nature of developmental processes.The editors of the book invited 36 chapters, written by the leading researchers in this area, and their contributions include detailed tutorials on the main topics, surveys of the state of the art in research, experimental results, and discussions of specific research goals. The main subjects addressed are sequence discovery, generation, and analysis; nanoconstructions and self-assembly; membrane computing; formal models and analysis; process calculi and automata; biochemical reactions; and other topics from natural computing, including molecular evolution, regulation of gene expression, light-based computing, cellular automata, realistic modelling of biological systems, and evolutionary computing. This subject is inherently interdisciplinary, and this book will be of value to researchers in computer science and biology who study the impact of the exciting mutual interaction between our understanding of bioprocesses and our understanding of computation.

Algorithmen sind der Kern der Informatik und der Mathematik, da jede Nutzung eines Computers erst durch Rechenverfahren überhaupt möglich wird. In diesem Buch, das in der englischen Originalausgabe schon lange ein Bestseller ist, gibt der Autor und sein Co-Autor umfassend und didaktisch geschickt Auskunft zu allen Fragen rund um das Thema Algorithmen, so z.B. zu Themen wie Berechenbarkeit, Korrektheit und Effizienz von Algorithmen, zu Programmiertechniken, und auch das aktuelle Thema Quantenrechnen wird behandelt. Das Buch kann als Grundlage eines einsemestrigen Einführungskurses in die Informatik dienen, oder als allgemeine Informatik-Einführung in den Naturwissenschaften, der Mathematik oder im Ingenieurwesen.

A fundamental understanding of algorithmic bioprocesses is key to learning how information processing occurs in nature at the cell level. The field is concerned with the interactions between computer science on the one hand and biology, chemistry, and DNA-oriented nanoscience on the other. In particular, this book offers a comprehensive overview of research into algorithmic self-assembly, RNA folding, the algorithmic foundations for biochemical reactions, and the algorithmic nature of developmental processes.The editors of the book invited 36 chapters, written by the leading researchers in this area, and their contributions include detailed tutorials on the main topics, surveys of the state of the art in research, experimental results, and discussions of specific research goals. The main subjects addressed are sequence discovery, generation, and analysis; nanoconstructions and self-assembly; membrane computing; formal models and analysis; process calculi and automata; biochemical reactions; and other topics from natural computing, including molecular evolution, regulation of gene expression, light-based computing, cellular automata, realistic modelling of biological systems, and evolutionary computing. This subject is inherently interdisciplinary, and this book will be of value to researchers in computer science and biology who study the impact of the exciting mutual interaction between our understanding of bioprocesses and our understanding of computation.

Computer science is the science of the future, and already underlies every facet of business and technology, and much of our everyday lives.

Computer science is the science of the future, and already underlies every facet of business and technology, and much of our everyday lives.

This book does not tell a story. Instead, it is about stories. Or rather, in technical terms, it is about scenarios. Scenarios of system behavior. It con­ centrates on reactive systems, be they software or hardware, or combined computer-embedded systems, including distributed and real-time systems. We propose a different way to program such systems, centered on inter­ object scenario-based behavior. The book describes a language, two tech­ niques, and a supporting tool. The language is a rather broad extension of live sequence charts (LSCs), the original version of which was proposed in 1998 by W. Damm and the first-listed author of this book. The first of the two techniques, called play-in, is a convenient way to 'play in' scenario­ based behavior directly from the system's graphical user interface (QUI). The second technique, play-out, makes it possible to execute, or 'play out', the behavior on the QUI as if it were programmed in a conventional intra­ object state-based fashion. All this is implemented in full in our tool, the Play-Engine. The book can be viewed as offering improvements in some ofthe phases of known system development life cycles, e.g., requirements capture and anal­ ysis, prototyping, and testing. However, there is a more radical way to view the book, namely, as proposing an alternative way to program reactivity, which, being based on inter-object scenarios, is a lot closer to how people think about systems and their behavior.

Können Computer alles? Wenn es so wäre, gäbe es dieses Buch nicht. Es beweist bestechend logisch, dass selbst die größten, schnellsten, intelligentesten und teuersten Computer der Welt nur beschränkt leistungsfähig sind. Der Mensch kann noch so viel Geld, Zeit und Know-how investieren, es gibt Computer-Probleme, die er niemals lösen wird. Eine beunruhigende, provokative Botschaft - und doch: wussten wir es nicht eigentlich schon, haben es aber nie wirklich glauben wollen? Der bekannte Computer-Wissenschaftler David Harel vermittelt die mathematischen Fakten spannend, unterhaltsam und allgemeinverständlich. Mit der Beschränktheit des Computers werden wir an die Grenzen allen Wissens geführt. Grenzen, die den Menschen beflügeln, das Mögliche weiter zu verbessern und selbst aus dem Unmöglichen Nutzen zu ziehen. Eine brillante tour de force mit überraschenden Aspekten, die den Leser - ob vorgebildeter Laie oder Fachkundiger - von der ersten bis zur letzten Seite fesselt.