Recently, contract-based design has been proposed as an “orthogonal” approach that complements system design methodologies proposed so far to cope with the complexity of system design. Contract-based design provides a rigorous scaffolding for verification, analysis, abstraction/refinement, and even synthesis. A number of results have been obtained in this domain but a unified treatment of the topic that can help put contract-based design in perspective was missing. This monograph intends to provide such a treatment where contracts are precisely defined and characterized so that they can be used in design methodologies with no ambiguity. In particular, this monograph identifies the essence of complex system design using contracts through a mathematical “meta-theory”, where all the properties of the methodology are derived from a very abstract and generic notion of contract. We show that the meta-theory provides deep and illuminating links with existing contract and interface theories, as well as guidelines for designing new theories. Our study encompasses contracts for both software and systems, with emphasis on the latter. We illustrate the use of contracts with two examples: requirement engineering for a parking garage management, and the development of contracts for timing and scheduling in the context of the AUTOSAR methodology in use in the automotive sector.

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Contracts for System Design

This paper offers a survey of uppaalsmc, a major extension of the real-time verification tool uppaal. uppaalsmc allows for the efficient analysis of performance properties of networks of priced timed automata under a natural stochastic semantics. In particular, uppaalsmc relies on a series of extensions of the statistical model checking approach generalized to handle real-time systems and estimate undecidable problems. uppaalsmc comes together with a friendly user interface that allows a user to specify complex problems in an efficient manner as well as to get feedback in the form of probability distributions and compare probabilities to analyze performance aspects of systems. The focus of the survey is on the evolution of the tool - including modeling and specification formalisms as well as techniques applied - together with applications of the tool to case studies.

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UPPAAL-SMC: Statistical Model Checking for Priced Timed Automata

This paper offers a survey of UPPAAL-SMC, a major extension of the real-time verification tool UPPAAL. UPPAAL-SMC allows for the efficient analysis of performance properties of networks of priced timed automata under a natural stochastic semantics. In particular, U PPAAL-SMC relies on a series of extensions of the statistical model checking app roach generalized to handle real-time systems and estimate undecidable problems. UPPAAL-SMC comes together with a friendly user interface that allows a user to specify complex problems in an efficient manner as well as to get feedback in the form of probability distributions and compare probabilities to analyze performance aspects of systems. The focus of the survey is on the evolution of the tool ‐ including modeling and specification formalisms as well as techniques applied ‐ tog ether with applications of the tool to case studies.

/pdf/uppaal-smc-statistical-model-checking-for-priced-timed-2uhx5lergw.pdf

UPPAAL-SMC: Statistical Model Checking for Priced Timed Automata ∗

We study the relation between specifications of component behaviors and contracts providing means to specify assumptions on environments as well as component guarantees. We show how a contract framework can be built in a generic way on top of any specification theory which supports composition and specification refinement. Our contract framework lifts refinement to the level of contracts and proposes a notion of contract composition on the basis of dominating contracts. Contract composition satisfies a universal property and can be constructively defined if the underlying specification theory is complete, i.e. it offers operators for quotienting and conjoining specifications. We illustrate our generic construction of contracts by moving a specification theory for modal transition systems to contracts and we show that a (previously proposed) trace-based contract theory is an instance of our framework.

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Moving from specifications to contracts in component-based design

In mean-payoff games, the objective of the protagonist is to ensure that the limit average of an infinite sequence of numeric weights is nonnegative. In energy games, the objective is to ensure that the running sum of weights is always nonnegative. Multi-mean-payoff and multi-energy games replace individual weights by tuples, and the limit average (resp., running sum) of each coordinate must be (resp., remain) nonnegative. We prove finite-memory determinacy of multi-energy games and show inter-reducibility of multi-mean-payoff and multi-energy games for finite-memory strategies. We improve the computational complexity for solving both classes with finite-memory strategies: we prove coNP-completeness improving the previous known EXPSPACE bound. For memoryless strategies, we show that deciding the existence of a winning strategy for the protagonist is NP-complete. We present the first solution of multi-mean-payoff games with infinite-memory strategies: we show that mean-payoff-sup objectives can be decided in NP ? coNP , whereas mean-payoff-inf objectives are coNP-complete.

The complexity of multi-mean-payoff and multi-energy games

Energy games have recently attracted a lot of attention. These are games played on finite weighted automata and concern the existence of infinite runs subject to boundary constraints on the accumulated weight, allowing e.g. only for behaviours where a resource is always available (nonnegative accumulated weight), yet does not exceed a given maximum capacity. We extend energy games to a multiweighted and parameterized setting, allowing us to model systems with multiple quantitative aspects. We present reductions between Petri nets and multiweighted automata and among different types of multiweighted automata and identify new complexity and (un)decidability results for both one- and two-player games. We also investigate the tractability of an extension of multiweighted energy games in the setting of timed automata.

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Energy games in multiweighted automata

Multiweighted energy games are two-player multiweighted games that concern the existence of infinite runs subject to a vector of lower and upper bounds on the accumulated weights along the run. We assume an unknown upper bound and calculate the set of vectors of upper bounds that allow an infinite run to exist. For both a strict and a weak upper bound we show how to construct this set by employing results from previous works, including an algorithm given by Valk and Jantzen for finding the set of minimal elements of an upward closed set. Additionally, we consider energy games where the weight of some transitions is unknown, and show how to find the set of suitable weights using the same algorithm.

Optimal bounds for multiweighted and parametrised energy games

Specification theories as a tool in the development process of component-based software systems have recently attracted a considerable attention. Current specification theories are however qualitative in nature and hence fragile and unsuited for modern software systems. We propose the first specification theory which allows to capture quantitative aspects during the refinement and implementation process.

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Quantitative refinement for weighted modal transition systems

We introduce a novel formalism of label-structured modal transition systems that combines the classical may/must modalities on transitions with structured labels that represent quantitative aspects of the model. On the one hand, the specification formalism is general enough to include models like weighted modal transition systems and allows system developers to employ more complex label refinement than in previously studied theories. On the other hand, the formalism maintains the desirable properties required by any specification theory supporting compositional reasoning. In particular, we study modal and thorough refinement, determinisation, parallel composition, conjunction, quotient and logical characterisation of label-structured modal transition systems.

Extending modal transition systems with structured labels

We propose weighted modal transition systems, an extension to the well-studied specification formalism of modal transition systems that allows to express both required and optional behaviours of their intended implementations. In our extension we decorate each transition with a weight interval that indicates the range of concrete weight values available to the potential implementations. In this way resource constraints can be modelled using the modal approach. We focus on two problems. First, we study the question of existence/finding the largest common refinement for a number of finite deterministic specifications and we show PSPACE-completeness of this problem. By constructing the most general common refinement, we allow for a stepwise and iterative construction of a common implementation. Second, we study a logical characterisation of the formalism and show that a formula in a natural weight extension of the logic CTL is satisfied by a given modal specification if and only if it is satisfied by all its refinements. The weight extension is general enough to express different sorts of properties that we want our weights to satisfy.

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Line Juhl

Papers

Energy games in multiweighted automata

Optimal bounds for multiweighted and parametrised energy games

Quantitative refinement for weighted modal transition systems

Extending modal transition systems with structured labels

Modal Transition Systems with Weight Intervals