Contract Refinement Research Articles

Composition of Behavioural Assume–Guarantee Contracts

The growing complexity of modern engineering systems necessitates a method for design and analysis that is inherently modular. Methods based on using contracts for system design have successfully tackled this issue for a variety of system classes, but mostly in the context of discrete software systems. Motivated by this, we present assume-guarantee contracts for continuous linear dynamical systems with inputs and outputs. Such contracts serve as system specifications through two aspects. The assumptions specify the dynamic behaviour of the environment of the system, which provides inputs for it, while the guarantees specify the desired dynamic behaviour of the output of the system when interconnected with a relevant environment. This is formalized by utilizing the behavioural approach to system theory. We define and characterize notions of contract implementation and contract refinement, where the latter is used to compare contracts. We also define and characterize two notions of contract composition that allow one to reason about two types of system interconnections: series and feedback. The properties of refinement and composition allow contracts to be used for modular design and analysis.

Asynchronous session subtyping as communicating automata refinement

We study the relationship between session types and behavioural contracts, representing Communicating Finite State Machines (CFSMs), under the assumption that processes communicate asynchronously. Session types represent a syntax-based approach for the description of communication protocols, while behavioural contracts, formally expressing CFSMs, follow an operational approach. We show the existence of a fully abstract interpretation of session types into a fragment of contracts that maps session subtyping into binary compliance-preserving CFSMs/behavioural contract refinement. In this way, on the one hand, we enrich the theory of session types with an operational characterization and, on the other hand, we use recent undecidability results for asynchronous session subtyping to obtain an original undecidability result for asynchronous CFSMs/behavioural contract refinement.

Article Review: The Policy Implementation of Waste to Energy Power Plant – Pilot Project in Surabaya, Indonesia

Indonesia government has nominated Surabaya city as one of the Indonesia pilot projects of waste to energy power plants (WEPP). The WEPP in Surabaya will start to operate in November 2019. However, to ensure this facility operates according to the regulation, the WEPP should be supported by good policy from the stakeholder. This research aims to review the policy implementation of WEPP in Surabaya pilot project based on Van Meter and Van Horn theory. The theory has several indicators that indicate good policy implementation. This research used a descriptive qualitative approach by interviewing fifteen respondents who involved in WEPP pilot project. The results suggest that the policy implementation of WEPP needs further regulation from local government about the management procedure of waste material, which converts to the tipping fee. The solution suggested from this issue is the contract refinement and the fundamental improvement of the communication system to the better WEPP.

Feature-oriented contract composition

A software product line comprises a set of products that share a common code base, but vary in specific characteristics called features. Ideally, features of a product line are developed in isolation and composed subsequently. Product lines are increasingly used for safety–critical software, for which quality assurance becomes indispensable. While the verification of product lines gained considerable interest in research over the last decade, the subject of how to specify product lines is only covered rudimentarily. A challenge to overcome is composition; similar to inheritance in object-oriented programming, features of a product line may refine other features along with their specifications. To investigate how refinement and composition of specifications can be established, we derive a notion of feature-oriented contracts comprising preconditions, postconditions, and framing conditions of a method. We discuss six mechanisms to perform contract composition between original and refining contracts. Moreover, we identify and discuss desired properties for contract composition and evaluate which properties are established by which mechanism. Our three main insights are that (a) contract refinement is seldom but crucial, (b) the Liskov principle does not apply to features, and (c) it is sufficient to accommodate techniques from object-orientation in the contract-composition mechanisms for handling frame refinements.

Tightening the contract refinements of a system architecture

Contract-based design is an emerging paradigm for correct-by-construction hierarchical systems: components are associated with assumptions and guarantees expressed as formal properties; the architecture is analyzed by verifying that each contract of composite components is correctly refined by the contracts of its subcomponents. The approach is very efficient, because the overall correctness proof is decomposed into proofs local to each component. However, the process for the contract specification and refinement is quite expensive because the requirements are formalised into formal properties, where part of the complexity is delegated to the designer, who has the burden of specifying the contracts. Typical problems include understanding which contracts are necessary, and how they can be simplified without breaking the correctness of the refinement and other refinements in case some subcontracts are shared. In this paper, we tackle these problems by proposing a technique to understand and simplify the contract refinements of a system architecture during the development process for the contract specification and refinement. The technique, called tightening, is based on parameter synthesis. The idea is to generate a set of parametric proof obligations, where each parameter evaluation corresponds to a variant of the original(s) contract refinement(s), and to search for tighter variants of the contracts that still ensure the correctness of the refinement(s). We cast this approach in the OCRA framework, where contracts are expressed with LTL formulas, and we evaluate its performance and effectiveness on a number of benchmarks.

Choreographies and Behavioural Contracts on the Way to Dynamic Updates

We survey our work on choreographies and behavioural contracts in multiparty interactions. In particular theories of behavioural contracts are presented which enable reasoning about correct service composition (contract compliance) and service substitutability (contract refinement preorder) under different assumptions concerning service communication: synchronous address or name based communication with patient non-preemptable or impatient invocations, or asynchronous communication. Correspondingly relations between behavioural contracts and choreographic descriptions are considered, where a contract for each communicating party is, e.g., derived by projection. The considered relations are induced as the maximal preoders which preserve contract compliance and global traces: we show maximality to hold (permitting services to be discovered/substituted independently for each party) when contract refinement preorders with all the above asymmetric communication means are considered and, instead, not to hold if the standard symmetric CCS/pi-calculus communication is considered (or when directly relating choreographies to behavioral contracts via a preorder, no matter the communication mean). The obtained maximal preorders are then characterized in terms of a new form of testing, called compliance testing, where not only tests must succeed but also the system under test (thus relating to controllability theory), and compared with classical preorders such as may/must testing, trace inclusion, etc. Finally, recent work about adaptable choreographies and behavioural contracts is presented, where the theory above is extended to update mechanisms allowing choreographies/contracts to be modified at run-time by internal (self-adaptation) or external intervention.

An Approach to Refining Active Components Based on Component Calculus

PDF HTML阅读 XML下载 导出引用 引用提醒 一种基于构件演算的主动构件精化方法 DOI: 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: Supported by the National Basic Research Program of China under Grant No.2002CB312001 (国家重点基础研究发展计划(973)); the National High-Tech Research and Development Plan of China under Grant No.2007AA010302 (国家高技术研究发展计划(863)); the Natural Science Foundation of Jiangsu Province of China under Grant No.BK2007714 (江苏省自然科学基金) An Approach to Refining Active Components Based on Component Calculus Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:现代构件系统通常包含多个并发执行的主动构件,这使得验证构件系统的正确性变得十分困难.通过对构件演算进行扩展,提出了一种主动构件的精化方法.在构件接口层引入契约.契约使用卫式设计描述公共方法和主动活动的功能规约.通过一对发散、失败集合定义契约的动态行为,并利用发散、失败集合之间的包含关系定义契约间的精化关系.证明了应用仿真技术确认契约精化关系的定理.定义构件的语义为其需求接口契约到其服务接口契约的函数,以此为基础,可以通过契约的精化来证明构件的精化.给出了构件的组装规则.在构件系统自底向上的构造过程中,应用构件的精化方法和组装规则可以保证最终系统的正确性. Abstract:Modern component-based systems consist of active components that execute in parallel, which brings great difficulties in verifying correctness. By extending component calculus, a theory concerning refinement of active components is proposed. For interfaces, contracts are introduced which give functional specifications for both public methods and active action in terms of guarded designs. Then, a contract's dynamic behavior is defined by a pair of divergences/failures sets. The refinement relation between contracts is defined as the set inclusion of their divergences/failures sets. The theories applying simulation techniques to assure the refinement relation are proved. By defining the semantics of a component as a mapping from the contract of its required interface to the contract of its provide interface, component refinement can be proved in terms of contract refinement. When the component- based systems are being constructed in a bottom-up manner, the application of the refinement method together with the composition rule can guarantee their correctness. 参考文献 相似文献 引证文献