The fast growth of cloud service offerings has attracted more enterprises to migrate their IT applications into cloud. Nonetheless, complex enterprise user requirements, especially interdependent relations across them, raise new challenges of cloud service selection. In addition, a major concern for these enterprises is ensuring compliance with their policies on the use of cloud services. In this paper, we present a systematic framework, based on formal verification and constraint solving techniques, to help enterprises tackle problems when adopting cloud computing. Our framework enables automatic detection of conflicts covering violation of enterprise policies and inconsistency of user requirements, and explanation generation which identifies problematic user requirements. The framework next select automatically cloud services which satisfy all enterprise policies and user requirements (with interdependent relations). We have prototyped and successfully applied our approach to projects which manage heterogeneous cloud infrastructure services for large enterprises.

Interval-based specification languages have been used to formally model and rigorously reason about real-time computing systems. This usually involves logical reasoning and mathematical computation with respect to continuous or discrete time. When these systems are complex, analyzing their models by hand becomes error-prone and difficult. In this article, we develop a verification system to facilitate the formal analysis of interval-based specification languages with machine-assisted proof support. The verification system is developed using a generic theorem prover, Prototype Verification System (PVS). Our system elaborately encodes a highly expressive set-based notation, Timed Interval Calculus (TIC), and can rigorously carry out the verification of TIC models at an interval level. We validated all TIC reasoning rules and discovered subtle flaws in the original rules. We also apply TIC to model Duration Calculus (DC), which is a popular interval-based specification language, and thus expand the capacity of the verification system. We can check the correctness of DC axioms, and execute DC proofs in a manner similar to the corresponding pencil-and-paper DC arguments.

High level specification languages like CSP use mathematical objects as abstractions to represent systems and processes. System behaviors are described as process expressions combined with compositional operators, which are associated with elegant algebraic laws for system analysis. Nonetheless, modeling systems with non-trivial data and functional aspects using CSP remains difficult. In this work, we propose a modeling language named CSP# (short for communicating sequential programs) which integrates high-level modeling operators with low-level procedural codes, for the purpose of efficient mechanical system verification. We demonstrate that data operations can be modeled as terminating sequential programs, which can be composed using high-level compositional operators. CSP# is supported by the PAT model checker and has been applied to a number of systems.

Abstract Simulink has been widely used in industry to model and simulate embedded systems. With the increasing usage of embedded systems in real-time safety-critical situations, Simulink becomes deficient to analyze (timing) requirements with high-level assurance. In this article, we apply Timed Interval Calculus (TIC), a real-time specification language, to complement Simulink with TIC formal verification capability. We elaborately construct TIC library functions to model Simulink library blocks which are used to compose Simulink diagrams. Next, Simulink diagrams are automatically transformed into TIC models which preserve functional and timing aspects. Important requirements such as timing bounded liveness can be precisely specified in TIC for whole diagrams or some components. Lastly, validation of TIC models can be rigorously conducted with a high degree of automation using a generic theorem prover. Our framework can enlarge the design space by representing environment properties to open systems, and handle complex diagrams as the analysis of continuous and discrete behavior is supported.

Timed Interval Calculus (TIC) is a highly expressive set-based notation for specifying and reasoning about embedded real-time systems. However, it lacks mechanical proving support, as its verification usually involves infinite time intervals and continuous dynamics. In this paper, we develop a system based on a generic theorem prover, Prototype Verification System (PVS), to assist formal verification of TIC at a high grade of automation. TIC semantics has been constructed by the PVS typed higher-order logic. Based on the encoding, we have checked all TIC reasoning rules and discovered subtle flaws. A translator has been implemented in Java to automatically transform TIC models into PVS specifications. A collection of supplementary rules and PVS strategies has been defined to facilitate the rigorous reasoning of TIC models with functional and non-functional (for example, real-time) requirements at the interval level. Our approach is generic and can be applied further to support other real-time notations.