Composing Families of Timed Automata

Featured Timed Automata (FTA) is a formalism that enables the verification of an entire Software Product Line (SPL), by capturing its behavior in a single model instead of product-by-product. However, it disregards compositional aspects inherent to SPL development. This paper introduces Interface FTA (IFTA), which extends FTA with variable interfaces that restrict the way automata can be composed, and with support for transitions with atomic multiple actions, simplifying the design. To support modular composition, a set of Reo connectors are modelled as IFTA. This separation of concerns increases reusability of functionality across products, and simplifies modelling, maintainability, and extension of SPLs. We show how IFTA can be easily translated into FTA and into networks of Timed Automata supported by UPPAAL. We illustrate this with a case study from the electronic government domain.POCI-01-0145-FEDER-016826. NORTE-01-0145-FEDER-00003

Indefinite waitings in MIRELA systems

MIRELA is a high-level language and a rapid prototyping framework dedicated to systems where virtual and digital objects coexist in the same environment and interact in real time. Its semantics is given in the form of networks of timed automata, which can be checked using symbolic methods. This paper shows how to detect various kinds of indefinite waitings in the components of such systems. The method is experimented using the PRISM model checker.Comment: In Proceedings ESSS 2015, arXiv:1506.0325

A refinement relation for families of timed automata

Software Product Lines (SPLs) are families of systems that share a high number of common assets while differing in others. In component-based systems, components themselves can be SPLs, i.e., each component can be seen as a family of variations, with different interfaces and functionalities, typically parameterized by a set of features and a feature model that specifies the valid combinations of features. This paper explores how to safely replace such families of components with more refined ones. We propose a notion of refinement for Interface Featured Timed Automata (IFTA), a formalism to model families of timed automata with support for multi-action transitions. We separate the notion of IFTA refinement into behavioral and variability refinement, i.e., the refinement of the underlying timed automata and feature model. Furthermore, we define behavioral refinement for the semantic level, i.e., transition systems, as an alternating simulation between systems, and lift this definition to IFTA refinement. We illustrate this notion with examples throughout the text and show that refinement is a pre-order and compositional.European Regional Development Fund (ERDF) through the Operational Programme for Competitiveness and Internationalisation (COMPETE 2020), and by National Funds through the Portuguese funding agency, FCT, within project TRUST, POCI-01-0145- FEDER-016826. In addition the first and second author are supported by FCT grants PD/BD/52238/2013 and SFRH/BPD/91908/2012, respectivel

From types to type requirements: Genericity for model-driven engineering

The final publication is available at Springer via http://dx.doi.org/10.1007/s10270-011-0221-0Model-driven engineering (MDE) is a software engineering paradigm that proposes an active use of models during the development process. This paradigm is inherently type-centric, in the sense that models and their manipulation are defined over the types of specific meta-models. This fact hinders the reuse of existing MDE artefacts with other meta-models in new contexts, even if all these meta-models share common characteristics. To increase the reuse opportunities of MDE artefacts, we propose a paradigm shift from type-centric to requirement-centric specifications by bringing genericity into models, meta-models and model management operations. For this purpose, we introduce so-called concepts gathering structural and behavioural requirements for models and meta-models. In this way, model management operations are defined over concepts, enabling the application of the operations to any meta-model satisfying the requirements imposed by the concept. Model templates rely on concepts to define suitable interfaces, hence enabling the definition of reusable model components. Finally, similar to mixin layers, templates can be defined at the meta-model level as well, to define languages in a modular way, as well as layers of functionality to be plugged-in into other meta-models. These ideas have been implemented in MetaDepth, a multi-level meta-modelling tool that integrates action languages from the Epsilon family for model management and code generation.This work has been sponsored by the Spanish Ministry of Science and Innovation with projects METEORIC (TIN2008-02081) and Go Lite (TIN2011-24139), and by the R&D program of the Community of Madrid with project “e-Madrid” (S2009/TIC-1650)

A virtual factory for smart city service integration

Tese de Doutoramento em Informática (MAP-i)In the context of smart cities, governments are investing efforts on creating public value through the development of digital public services (DPS) focusing on specific policy areas, such as transport. Main motivations to deliver DPS include reducing administrative burdens and costs, increasing effectiveness and efficiency of government processes, and improving citizens’ quality of life through enhanced services and simplified interactions with governments. To ensure effective planning and design of DPS in a given domain, governments face several challenges, like the need of specialized tools to facilitate the effective planning and the rapid development of DPS, as well as, tools for service integration, affording high development costs, and ensuring DPS conform with laws and regulations. These challenges are exacerbated by the fact that many public administrations develop tailored DPS, disregarding the fact that services share common functionality and business processes. To address the above challenges, this thesis focuses on leveraging the similarities of DPS and on applying a Software Product Line (SPL) approach combined with formal methods techniques for specifying service models and verifying their behavioural properties. In particular, the proposed solution introduces the concept of a virtual factory for the planning and rapid development of DPS in a given smart city domain. The virtual factory comprises a framework including software tools, guidelines, practices, models, and other artefacts to assist engineers to automate and make more efficient the development of a family of DPS. In this work the virtual factory is populated with tools for government officials and software developers to plan and design smart mobility services, and to rapidly model DPS relying on SPLs and components-base development techniques. Specific contributions of the thesis include: 1) the concept of virtual factory; 2) a taxonomy for planning and designing smart mobility services; 3) an ontology to fix a common vocabulary for a specific family of DPS; 4) a compositional formalism to model SPLs, to serve as a specification language for DPS; and 5) a variable semantics for a coordination language to simplify coordination of services in the context of SPLs.No contexto das cidades inteligentes, os governos investem esforços na criação de valor público através do desenvolvimento de serviços públicos digitais (DPS), concentrandose em áreas políticas específicas, como os transportes. As principais motivações para entregar o DPS incluem a redução de custos administrativos, o aumento da eficácia dos processos do governo e a melhoria da qualidade de vida dos cidadãos através de serviços melhorados e interações simplificadas com os governos. Para garantir um planeamento efetivo do DPS num determinado domínio, os governos enfrentam vários desafios, como a necessidade de ferramentas especializadas para facilitar o planeamento eficaz e o rápido desenvolvimento do DPS, bem como ferramentas para integração de DPS, reduzindo altos custos de desenvolvimento e garantindo que os DPS estejam em conformidade com as leis e regulamentos. Esses desafios são exacerbados pelo fato de que muitas administrações públicas desenvolvem o DPS sob medida, desconsiderando o fato de que os serviços compartilham funcionalidade e processos de negócios comuns. Para enfrentar os desafios, esta tese concentra-se em aproveitar as semelhanças dos DPS aplicando uma abordagem de Software Product Lines (SPL) combinada com métodos formais para especificar modelos de DPS e verificar propriedades. Em particular, introduz o conceito de uma fábrica virtual (VF) para o planeamento e desenvolvimento rápido de DPS num domínio de cidade inteligente. A VF compreende ferramentas de software, diretrizes, modelos e outros artefatos para auxiliar os engenheiros a automatizar e tornar mais eficiente o desenvolvimento de uma família de DPS. Neste trabalho, a VF é preenchida com ferramentas para várias partes para planear e projetar serviços de mobilidade inteligente (MI), e modelar rapidamente o DPS com base em SPLs e técnicas de desenvolvimento baseadas em componentes. Contribuições específicas da tese incluem: 1) o conceito de VF; 2) uma taxonomia para planear serviços de MI; 3) uma ontologia para fixar um vocabulário comum para uma família específica de DPS; 4) um formalismo composicional para modelar SPLs, e servir como uma linguagem de especificação para DPS; e 5) uma semântica variável para uma linguagem de coordenação para simplificar a coordenação.This work was funded by FCT – Foundation for Science and Technology, the Portuguese Ministry of Science, Technology and Higher Education, through the Operational Programme for Human Capital (POCH). Grant reference: PD/BD/52238/201

Behavioural equivalences for timed systems

Timed transition systems are behavioural models that include an explicit treatment of time flow and are used to formalise the semantics of several foundational process calculi and automata. Despite their relevance, a general mathematical characterisation of timed transition systems and their behavioural theory is still missing. We introduce the first uniform framework for timed behavioural models that encompasses known behavioural equivalences such as timed bisimulations, timed language equivalences as well as their weak and time-abstract counterparts. All these notions of equivalences are naturally organised by their discriminating power in a spectrum. We prove that this result does not depend on the type of the systems under scrutiny: it holds for any generalisation of timed transition system. We instantiate our framework to timed transition systems and their quantitative extensions such as timed probabilistic systems

Modeling Computational Security in Long-Lived Systems, Version 2

For many cryptographic protocols, security relies on the assumption that adversarial entities have limited computational power. This type of security degrades progressively over the lifetime of a protocol. However, some cryptographic services, such as timestamping services or digital archives, are long-lived in nature; they are expected to be secure and operational for a very long time (i.e., super-polynomial). In such cases, security cannot be guaranteed in the traditional sense: a computationally secure protocol may become insecure if the attacker has a super-polynomial number of interactions with the protocol. This paper proposes a new paradigm for the analysis of long-lived security protocols. We allow entities to be active for a potentially unbounded amount of real time, provided they perform only a polynomial amount of work per unit of real time. Moreover, the space used by these entities is allocated dynamically and must be polynomially bounded. We propose a new notion of long-term implementation, which is an adaptation of computational indistinguishability to the long-lived setting. We show that long-term implementation is preserved under polynomial parallel composition and exponential sequential composition. We illustrate the use of this new paradigm by analyzing some security properties of the long-lived timestamping protocol of Haber and Kamat

Complexity Hierarchies Beyond Elementary

We introduce a hierarchy of fast-growing complexity classes and show its suitability for completeness statements of many non elementary problems. This hierarchy allows the classification of many decision problems with a non-elementary complexity, which occur naturally in logic, combinatorics, formal languages, verification, etc., with complexities ranging from simple towers of exponentials to Ackermannian and beyond.Comment: Version 3 is the published version in TOCT 8(1:3), 2016. I will keep updating the catalogue of problems from Section 6 in future revision