Richer Interface Automata with Optimistic and Pessimistic Compatibility

Modal transition systems are a popular semantic underpinning of interface theories, such as Nyman et al.’s IOMTS and Bauer et al.’s MIO, which facilitate component-based reasoning of concurrent systems. Our interface theory MIA repaired a compositional flaw of IOMTS-refinement and introduced a conjunction operator. In this paper, we first modify MIA to properly deal with internal computations including internal must-transitions, which were largely ignored already in IOMTS. We then study a MIA variant that adopts MIO’s pessimistic – rather than IOMTS’ optimistic – view on component compatibility and define, for the first time in a pessimistic, non-deterministic setting, conjunction and disjunction on interfaces. For the pessimistic MIA variant we also provide a mechanism for extending alphabets when refining interfaces, which is a desired feature in practice. We illustrate our advancements via a small example

Communication requirements for team automata

Compatibility of components is an important issue in the quest for systems of systems that guarantee successful communications, free from message loss and indefinite waiting for inputs. In this paper, we investigate compatibility in the context of systems consisting of reactive components which may communicate through the synchronised execution of common actions. We model such systems in the team automata framework, which does not impose any a priori restrictions on the synchronisation policy followed to combine the components. We identify a family of representative synchronisation types based on the number of sending and receiving components participating in synchronisations. Then, we provide a generic procedure to derive, for each synchronisation type, requirements for receptiveness and for responsiveness of team automata that prevent that outputs are not accepted and inputs are not provided, respectively. Due to the genericity of our approach w.r.t. synchronisation policies, we can capture compatibility notions for various multi-component system models known from the literature.Peer ReviewedPostprint (author's final draft

A Generalised Theory of Interface Automata, Component Compatibility and Error

Interface theories allow systems designers to reason about the composability and compatibility of concurrent system components. Such theories often extend both de Alfaro and Henzinger’s Interface Automata and Larsen’s Modal Transition Systems, which leads, however, to several issues that are undesirable in practice: an unintuitive treatment of specified unwanted behaviour, a binary compatibility concept that does not scale to multi-component assemblies, and compatibility guarantees that are insufficient for software product lines. In this paper we show that communication mismatches are central to all these problems and, thus, the ability to represent such errors semantically is an important feature of an interface theory. Accordingly, we present the error-aware interface theory EMIA, where the above shortcomings are remedied by introducing explicit fatal error states. In addition, we prove via a Galois insertion that EMIA is a conservative generalisation of the established MIA (Modal Interface Automata) theory

Modal Interface Theories for Specifying Component-based Systems

Large software systems frequently manifest as complex, concurrent, reactive systems and their correctness is often crucial for the safety of the application. Hence, modern techniques of software engineering employ incremental, component-based approaches to systems design. These are supported by interface theories which may serve as specification languages and as semantic foundations for software product lines, web-services, the internet of things, software contracts and conformance testing. Interface theories enable a systems designer to express communication requirements of components on their environments and to reason about the mutual compatibility of these requirements in order to guarantee the communication safety of the system. Further, interface theories enrich traditional operational specification theories by declarative aspects such as conjunction and disjunction, which allow one to specify systems heterogeneously. However, substantial practical aspects of software verification are not supported by current interface theories, e.g., reusing components, adapting components to changed operational environments, reasoning about the compatibility of more than two components, modelling software product lines or tracking erroneous behaviour in safety-critical systems. The goal of this thesis is to investigate the theoretical foundations for making interface theories more practical by solving the above issues. Although partial solutions to some of these issues have been presented in the literature, none of them succeeds without sacrificing other desired features. The particular challenge of this thesis is to solve these problems simultaneously within a single interface theory. To this end, the arguably most general interface theory Modal Interface Automata (MIA) is extended, yielding the interface theory Error-preserving Modal Interface Automata (EMIA). The above problems are addressed as follows. Quotient operators are adjoint to composition and, therefore, support component reuse. Such a quotient operator is introduced to both MIA and EMIA. It is the first one that considers nondeterministic dividends and compatibility. Alphabet extension operators for MIA and EMIA allow for the change of operational environment by permitting one to adapt system components to new interactions without breaking previously satisfied requirements. Erroneous behavior is identified as a common source of problems with respect to the compatibility of more than two components, the modelling of software product lines and erroneous behaviour in safety-critical systems. EMIA improves on previous interface theories by providing a more precise semantics with respect to erroneous behaviour based on error-preservation. The relation between error-preservation and the usual error-abstraction employed in previous interface theories is investigated, establishing a Galois insertion from MIA into EMIA that is relevant at the levels of specifications, composition operations and proofs. The practical utility of interface theories is demonstrated by providing a software implementation of MIA and EMIA that is applied to two case studies. Further, an outlook is given on the relation between type checking and refinement checking. As a proof of concept, the simple interface theory Interface Automata is extended to a behavioural type theory where type checking is a syntactic approximation of refinement checking.Große Softwaresysteme bilden häufig komplexe, nebenläufige, reaktive Systeme, deren Korrektheit für die Sicherheit der Anwendung entscheidend ist. Daher setzen moderne Verfahren der Softwaretechnik inkrementelle, komponentenbasierte Ansätze zum Software-Entwurf ein. Diese werden von Interface-Theorien unterstützt, die als Spezifikationssprachen und semantische Grundlagen für Softwareproduktlinien, Web-Services, das Internet der Dinge, Softwarekontrakte und Konformanztests dienen können. Interface-Theorien ermöglichen es, Kommunikationsanforderungen von Komponenten an ihre Umgebung auszudrücken, um die gegenseitige Kompatibilität dieser Anforderungen zu überprüfen und die Kommunikationssicherheit des Systems zu garantieren. Zudem erweitern Interface-Theorien traditionelle operationale Spezifikationstheorien um deklarative Aspekte wie beispielsweise Konjunktion und Disjunktion, die heterogenes Spezifizieren ermöglichen. Allerdings werden wesentliche praktische Aspekte der Softwareverifikation von Interface-Theorien nicht unterstützt, z.B. das Wiederverwenden von Komponenten, das Anpassen von Komponenten an geänderte operationale Umgebungen, die Kompatibilitätsprüfung von mehr als zwei Komponenten, das Modellieren von Softwareproduktlinien oder das Zurückverfolgen von Fehlverhalten sicherheitskritischer Systeme. Diese Arbeit untersucht die theoretischen Grundlagen von Interface-Theorien mit dem Ziel, die oben genannten praktischen Probleme zu lösen. Obwohl es in der Literatur Teillösungen zu manchen dieser Probleme gibt, erreicht keine davon ihr Ziel, ohne andere wünschenswerte Eigenschaften aufzugeben. Die besondere Herausforderung dieser Arbeit besteht darin, diese Probleme innerhalb einer einzigen Interface-Theorie zugleich zu lösen. Zu diesem Zweck wurde die wohl allgemeinste Interface-Theorie Modal Interface Automata (MIA) zu der Interface-Theorie Error-preserving Modal Interface Automata (EMIA) weiterentwickelt. Die obigen Probleme werden wie folgt gelöst. Ein zur Komposition adjungierter Quotientenoperator, der das Wiederverwenden von Komponenten ermöglicht, wurde für MIA und EMIA eingeführt. Es handelt sich dabei um den ersten Quotientenoperator, der nichtdeterministische Dividenden und Kompatibilität betrachtet. Alphabeterweiterungsoperatoren erlauben eine Änderung der operationalen Umgebung, indem sie es ermöglichen, Komponenten an neue Interaktionen anzupassen, ohne zuvor erfüllte Anforderungen zu missachten. Fehlerhaftes Verhalten wird als eine gemeinsame Ursache von Problemen bezüglich der Kompatibilität von mehr als zwei Komponenten, der Modellierung von Softwareproduktlinien und des Fehlverhaltens sicherheitskritischer Systeme erkannt. EMIA verbessert bisherige Interface-Theorien durch eine präzisere Fehlersemantik, die auf dem Erhalten von Fehlern beruht. Als Beziehung zwischen diesem Fehlererhalt und der in bisherigen Interface-Theorien üblichen Fehlerabstraktion ergibt sich eine Galois-Einbettung von MIA in EMIA, die auf den Ebenen der Spezifikationen, Operatoren und Beweise relevant ist. Die praktische Anwendbarkeit von Interface-Theorien wird mittels einer Implementierung von MIA und EMIA als Software und deren Anwendung auf zwei Fallstudien demonstriert. Zudem wird das Verhältnis zwischen Verfeinerung und Typprüfung diskutiert. In einer Machbarkeitsstudie wurde die einfache Interface-Theorie Interface Automata zu einer Verhaltenstyptheorie erweitert, bei der die Typprüfung eine syntaktische Approximation der Verfeinerung ist

Fundamental Approaches to Software Engineering

This open access book constitutes the proceedings of the 23rd International Conference on Fundamental Approaches to Software Engineering, FASE 2020, which took place in Dublin, Ireland, in April 2020, and was held as Part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2020. The 23 full papers, 1 tool paper and 6 testing competition papers presented in this volume were carefully reviewed and selected from 81 submissions. The papers cover topics such as requirements engineering, software architectures, specification, software quality, validation, verification of functional and non-functional properties, model-driven development and model transformation, software processes, security and software evolution