Exploiting the Hierarchical Structure of Rule-Based Specifications for Decision Planning

Rule-based specifications have been very successful as a declarative approach in many domains, due to the handy yet solid foundations offered by rule-based machineries like term and graph rewriting. Realistic problems, however, call for suitable techniques to guarantee scalability. For instance, many domains exhibit a hierarchical structure that can be exploited conveniently. This is particularly evident for composition associations of models. We propose an explicit representation of such structured models and a methodology that exploits it for the description and analysis of model- and rule-based systems. The approach is presented in the framework of rewriting logic and its efficient implementation in the rewrite engine Maude and is illustrated with a case study.

A Component-oriented Framework for Autonomous Agents

The design of a complex system warrants a compositional methodology, i.e., composing simple components to obtain a larger system that exhibits their collective behavior in a meaningful way. We propose an automaton-based paradigm for compositional design of such systems where an action is accompanied by one or more preferences. At run-time, these preferences provide a natural fallback mechanism for the component, while at design-time they can be used to reason about the behavior of the component in an uncertain physical world. Using structures that tell us how to compose preferences and actions, we can compose formal representations of individual components or agents to obtain a representation of the composed system. We extend Linear Temporal Logic with two unary connectives that reflect the compositional structure of the actions, and show how it can be used to diagnose undesired behavior by tracing the falsification of a specification back to one or more culpable components

Abstract Constraint Data Types

Martin Wirsing is one of the earliest contributors to the area of Algebraic Specification (e.g., [2]), which he explored in a variety of domains over many years. Throughout his career, he has also inspired countless researchers in related areas. This paper is inspired by one of the domains that he explored thirty years or so after his first contributions when leading the FET Integrated Project SENSORIA [14]: the use of constraint systems to deal with non-functional requirements and preferences [13,8]. Following in his footsteps, we provide an extension of the traditional notion of algebraic data type specification to encompass soft-constraints as formalised in [1]. Finally, we relate this extension with institutions [6] and recent work on graded consequence in institutions [3].Peer ReviewedPostprint (author’s final draft

Many-Valued Institutions for Constraint Specification

We advance a general technique for enriching logical systems with soft constraints, making them suitable for specifying complex software systems where parts are put together not just based on how they meet certain functional requirements but also on how they optimise certain constraints. This added expressive power is required, for example, for capturing quality attributes that need to be optimised or, more generally, for formalising what are usually called service-level agreements. More specifically, we show how institutions endowed with a graded semantic consequence can accommodate soft-constraint satisfaction problems. We illustrate our approach by showing how, in the context of service discovery, one can quantify the compatibility of two specifications and thus formalise the selection of the most promising provider of a required resource.Peer Reviewe

How To Touch a Running System

The increasing importance of distributed and decentralized software architectures entails more and more attention for adaptive software. Obtaining adaptiveness, however, is a difficult task as the software design needs to foresee and cope with a variety of situations. Using reconfiguration of components facilitates this task, as the adaptivity is conducted on an architecture level instead of directly in the code. This results in a separation of concerns; the appropriate reconfiguration can be devised on a coarse level, while the implementation of the components can remain largely unaware of reconfiguration scenarios. We study reconfiguration in component frameworks based on formal theory. We first discuss programming with components, exemplified with the development of the cmc model checker. This highly efficient model checker is made of C++ components and serves as an example for component-based software development practice in general, and also provides insights into the principles of adaptivity. However, the component model focuses on high performance and is not geared towards using the structuring principle of components for controlled reconfiguration. We thus complement this highly optimized model by a message passing-based component model which takes reconfigurability to be its central principle. Supporting reconfiguration in a framework is about alleviating the programmer from caring about the peculiarities as much as possible. We utilize the formal description of the component model to provide an algorithm for reconfiguration that retains as much flexibility as possible, while avoiding most problems that arise due to concurrency. This algorithm is embedded in a general four-stage adaptivity model inspired by physical control loops. The reconfiguration is devised to work with stateful components, retaining their data and unprocessed messages. Reconfiguration plans, which are provided with a formal semantics, form the input of the reconfiguration algorithm. We show that the algorithm achieves perceived atomicity of the reconfiguration process for an important class of plans, i.e., the whole process of reconfiguration is perceived as one atomic step, while minimizing the use of blocking of components. We illustrate the applicability of our approach to reconfiguration by providing several examples like fault-tolerance and automated resource control

Algorithmic composition of music in real-time with soft constraints

Music has been the subject of formal approaches for a long time, ranging from Pythagoras’ elementary research on tonal systems to J. S. Bach’s elaborate formal composition techniques. Especially in the 20th century, much music was composed based on formal techniques: Algorithmic approaches for composing music were developed by composers like A. Schoenberg as well as in the scientific area. So far, a variety of mathematical techniques have been employed for composing music, e.g. probability models, artificial neural networks or constraint-based reasoning. In the recent time, interactive music systems have become popular: existing songs can be replayed with musical video games and original music can be interactively composed with easy-to-use applications running e.g. on mobile devices. However, applications which algorithmically generate music in real-time based on user interaction are mostly experimental and limited in either interactivity or musicality. There are many enjoyable applications but there are also many opportunities for improvements and novel approaches. The goal of this work is to provide a general and systematic approach for specifying and implementing interactive music systems. We introduce an algebraic framework for interactively composing music in real-time with a reasoning-technique called ‘soft constraints’: this technique allows modeling and solving a large range of problems and is suited particularly well for problems with soft and concurrent optimization goals. Our framework is based on well-known theories for music and soft constraints and allows specifying interactive music systems by declaratively defining ‘how the music should sound’ with respect to both user interaction and musical rules. Based on this core framework, we introduce an approach for interactively generating music similar to existing melodic material. With this approach, musical rules can be defined by playing notes (instead of writing code) in order to make interactively generated melodies comply with a certain musical style. We introduce an implementation of the algebraic framework in .NET and present several concrete applications: ‘The Planets’ is an application controlled by a table-based tangible interface where music can be interactively composed by arranging planet constellations. ‘Fluxus’ is an application geared towards musicians which allows training melodic material that can be used to define musical styles for applications geared towards non-musicians. Based on musical styles trained by the Fluxus sequencer, we introduce a general approach for transforming spatial movements to music and present two concrete applications: the first one is controlled by a touch display, the second one by a motion tracking system. At last, we investigate how interactive music systems can be used in the area of pervasive advertising in general and how our approach can be used to realize ‘interactive advertising jingles’.Musik ist seit langem Gegenstand formaler Untersuchungen, von Phytagoras‘ grundlegender Forschung zu tonalen Systemen bis hin zu J. S. Bachs aufwändigen formalen Kompositionstechniken. Vor allem im 20. Jahrhundert wurde vielfach Musik nach formalen Methoden komponiert: Algorithmische Ansätze zur Komposition von Musik wurden sowohl von Komponisten wie A. Schoenberg als auch im wissenschaftlichem Bereich entwickelt. Bislang wurde eine Vielzahl von mathematischen Methoden zur Komposition von Musik verwendet, z.B. statistische Modelle, künstliche neuronale Netze oder Constraint-Probleme. In der letzten Zeit sind interaktive Musiksysteme populär geworden: Bekannte Songs können mit Musikspielen nachgespielt werden, und mit einfach zu bedienenden Anwendungen kann man neue Musik interaktiv komponieren (z.B. auf mobilen Geräten). Allerdings sind die meisten Anwendungen, die basierend auf Benutzerinteraktion in Echtzeit algorithmisch Musik generieren, eher experimentell und in Interaktivität oder Musikalität limitiert. Es gibt viele unterhaltsame Anwendungen, aber ebenso viele Möglichkeiten für Verbesserungen und neue Ansätze. Das Ziel dieser Arbeit ist es, einen allgemeinen und systematischen Ansatz zur Spezifikation und Implementierung von interaktiven Musiksystemen zu entwickeln. Wir stellen ein algebraisches Framework zur interaktiven Komposition von Musik in Echtzeit vor welches auf sog. ‚Soft Constraints‘ basiert, einer Methode aus dem Bereich der künstlichen Intelligenz. Mit dieser Methode ist es möglich, eine große Anzahl von Problemen zu modellieren und zu lösen. Sie ist besonders gut geeignet für Probleme mit unklaren und widersprüchlichen Optimierungszielen. Unser Framework basiert auf gut erforschten Theorien zu Musik und Soft Constraints und ermöglicht es, interaktive Musiksysteme zu spezifizieren, indem man deklarativ angibt, ‚wie sich die Musik anhören soll‘ in Bezug auf sowohl Benutzerinteraktion als auch musikalische Regeln. Basierend auf diesem Framework stellen wir einen neuen Ansatz vor, um interaktiv Musik zu generieren, die ähnlich zu existierendem melodischen Material ist. Dieser Ansatz ermöglicht es, durch das Spielen von Noten (nicht durch das Schreiben von Programmcode) musikalische Regeln zu definieren, nach denen interaktiv generierte Melodien an einen bestimmten Musikstil angepasst werden. Wir präsentieren eine Implementierung des algebraischen Frameworks in .NET sowie mehrere konkrete Anwendungen: ‚The Planets‘ ist eine Anwendung für einen interaktiven Tisch mit der man Musik komponieren kann, indem man Planetenkonstellationen arrangiert. ‚Fluxus‘ ist eine Anwendung, die sich an Musiker richtet. Sie erlaubt es, melodisches Material zu trainieren, das wiederum als Musikstil in Anwendungen benutzt werden kann, die sich an Nicht-Musiker richten. Basierend auf diesen trainierten Musikstilen stellen wir einen generellen Ansatz vor, um räumliche Bewegungen in Musik umzusetzen und zwei konkrete Anwendungen basierend auf einem Touch-Display bzw. einem Motion-Tracking-System. Abschließend untersuchen wir, wie interaktive Musiksysteme im Bereich ‚Pervasive Advertising‘ eingesetzt werden können und wie unser Ansatz genutzt werden kann, um ‚interaktive Werbejingles‘ zu realisieren

Twenty years of rewriting logic

AbstractRewriting logic is a simple computational logic that can naturally express both concurrent computation and logical deduction with great generality. This paper provides a gentle, intuitive introduction to its main ideas, as well as a survey of the work that many researchers have carried out over the last twenty years in advancing: (i) its foundations; (ii) its semantic framework and logical framework uses; (iii) its language implementations and its formal tools; and (iv) its many applications to automated deduction, software and hardware specification and verification, security, real-time and cyber-physical systems, probabilistic systems, bioinformatics and chemical systems

Which Soft Constraints do you Prefer?

Soft constraints are gaining popularity in diverse areas such as orchestration of Web services or optimization of scheduling decisions. However, current approaches to soft constraints preclude them from modelling certain decision problems with multiple preference criteria. We propose a new approach to soft constraints which allows a natural expression of these problems, describe an implementation in the rewriting logic system Maude, and prove its correctness