A Complete Axiom System for Propositional Interval Temporal Logic with Infinite Time

Interval Temporal Logic (ITL) is an established temporal formalism for reasoning about time periods. For over 25 years, it has been applied in a number of ways and several ITL variants, axiom systems and tools have been investigated. We solve the longstanding open problem of finding a complete axiom system for basic quantifier-free propositional ITL (PITL) with infinite time for analysing nonterminating computational systems. Our completeness proof uses a reduction to completeness for PITL with finite time and conventional propositional linear-time temporal logic. Unlike completeness proofs of equally expressive logics with nonelementary computational complexity, our semantic approach does not use tableaux, subformula closures or explicit deductions involving encodings of omega automata and nontrivial techniques for complementing them. We believe that our result also provides evidence of the naturalness of interval-based reasoning

Improving Cloud System Reliability Using Autonomous Agent Technology

Cloud computing platforms provide efficient and flexible ways to offer services and computation facilities to users. Service providers acquire resources according to their requirements and deploy their services in cloud. Service consumers can access services over networks. In cloud computing, virtualization techniques allow cloud providers provide computation and storage resources according to users’ requirement. However, reliability in the cloud is an important factor to measure the performance of a virtualized cloud computing platform. Reliability in cloud computing includes the usability and availability. Usability is defined as cloud computing platform provides functional and easy-to-use computation resources to users. In order to ensure usability, configurations and management policies have to be maintained and deployed by cloud computing providers. Availability of cloud is defined as cloud computing platform provides stable and reliable computation resources to users. My research concentrates on improving usability and availability of cloud computing platforms. I proposed a customized agent-based reliability monitoring framework to increase reliability of cloud computing

Verification of real-time systems : improving tool support

We address a number of limitations of Timed Automata and real-time model-checkers, which undermine the reliability of formal verification. In particular, we focus on the model-checker Uppaal as a representative of this technology. Timelocks and Zeno runs represent anomalous behaviours in a timed automaton, and may invalidate the verification of safety and liveness properties. Currently, model-checkers do not offer adequate support to prevent or detect such behaviours. In response, we develop new methods to guarantee timelock-freedom and absence of Zeno runs, which improve and complement the existent support. We implement these methods in a tool to check Uppaal specifications. The requirements language of model-checkers is not well suited to express sequence and iteration of events, or past computations. As a result, validation problems may arise during verification (i.e., the property that we verify may not accurately reflect the intended requirement). We study the logic PITL, a rich propositional subset of Interval Temporal Logic, where these requirements can be more intuitively expressed than in model-checkers. However, PITL has a decision procedure with a worst-case non-elementary complexity, which has hampered the development of efficient tool support. To address this problem, we propose (and implement) a translation from PITL to the second-order logic WS1S, for which an efficient decision procedure is provided by the tool MONA. Thanks to the many optimisations included in MONA, we obtain an efficient decision procedure for PITL, despite its non-elementary complexity. Data variables in model-checkers are restricted to bounded domains, in order to obtain fully automatic verification. However, this may be too restrictive for certain kinds of specifications (e.g., when we need to reason about unbounded buffers). In response, we develop the theory of Discrete Timed Automata as an alternative formalism for real-time systems. In Discrete Timed Automata, WS1S is used as the assertion language, which enables MONA to assist invariance proofs. Furthermore, the semantics of urgency and synchronisation adopted in Discrete Timed Automata guarantee, by construction, that specifications are free from a large class of timelocks. Thus, we argue that well-timed specifications are easier to obtain in Discrete Timed Automata than in Timed Automata and most other notations for real-time systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo