Bisimulations Up-to for the Linear Time Branching Time Spectrum

Coinductive definitions of semantics based on bisimulations have rather pleasant properties and are simple to use. In order to get coinductive characterisations of those semantic equivalences that are weaker than strong bisimulation we use a variant of the bisimulation up-to technique in which we allow the use of a given preorder relation. We prove that under some technical conditions our bisimulations up-to characterise the kernel of the given preorder. It is remarkable that the adequate orientation of the ordering relation is crucial to get this result. As a corollary, we get nice coinductive characterisations of all the axiomatic semantic equivalences in Van Glabbeek’s spectrum. Although we first prove our results for finite processes, reasoning by induction, then we see, by using continuity arguments, that they are also valid for infinite (finitary) processes

Speculative execution by using software transactional memory

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do Grau de Mestre em Engenharia Informática.Many programs sequentially execute operations that take a long time to complete. Some of these operations may return a highly predictable result. If this is the case, speculative execution can improve the overall performance of the program. Speculative execution is the execution of code whose result may not be needed. Generally it is used as a performance optimization. Instead of waiting for the result of a costly operation,speculative execution can be used to speculate the operation most probable result and continue executing based in this speculation. If later the speculation is confirmed to be correct, time had been gained. Otherwise, if the speculation is incorrect, the execution based in the speculation must abort and re-execute with the correct result. In this dissertation we propose the design of an abstract process to add speculative execution to a program by doing source-to-source transformation. This abstract process is used in the definition of a mechanism and methodology that enable programmer to add speculative execution to the source code of programs. The abstract process is also used in the design of an automatic source-to-source transformation process that adds speculative execution to existing programs without user intervention. Finally, we also evaluate the performance impact of introducing speculative execution in database clients. Existing proposals for the design of mechanisms to add speculative execution lacked portability in favor of performance. Some were designed to be implemented at kernel or hardware level. The process and mechanisms we propose in this dissertation can add speculative execution to the source of program, independently of the kernel or hardware that is used. From our experiments we have concluded that database clients can improve their performance by using speculative execution. There is nothing in the system we propose that limits in the scope of database clients. Although this was the scope of the case study, we strongly believe that other programs can benefit from the proposed process and mechanisms for introduction of speculative execution

A distributed analysis and monitoring framework for the compact Muon solenoid experiment and a pedestrian simulation

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The design of a parallel and distributed computing system is a very complicated task. It requires a detailed understanding of the design issues and of the theoretical and practical aspects of their solutions. Firstly, this thesis discusses in detail the major concepts and components required to make parallel and distributed computing a reality. A multithreaded and distributed framework capable of analysing the simulation data produced by a pedestrian simulation software was developed. Secondly, this thesis discusses the origins and fundamentals of Grid computing and the motivations for its use in High Energy Physics. Access to the data produced by the Large Hadron Collider (LHC) has to be provided for more than five thousand scientists all over the world. Users who run analysis jobs on the Grid do not necessarily have expertise in Grid computing. Simple, userfriendly and reliable monitoring of the analysis jobs is one of the key components of the operations of the distributed analysis; reliable monitoring is one of the crucial components of the Worldwide LHC Computing Grid for providing the functionality and performance that is required by the LHC experiments. The CMS Dashboard Task Monitoring and the CMS Dashboard Job Summary monitoring applications were developed to serve the needs of the CMS community

(Bi)Simulations Up-to Characterise Process Semantics

We define (bi)simulations up-to a preorder and show how we can use them to provide a coinductive, (bi)simulation-like, characterisation of semantic (equivalences) preorders for processes. In particular, we can apply our results to all the semantics in the linear time-branching time spectrum that are defined by preorders coarser than the ready simulation preorder. The relation between bisimulations up-to and simulations up-to allows us to find some new relations between the equivalences that define the semantics and the corresponding preorders. In particular, we have shown that the simulation up-to an equivalence relation is a canonical preorder whose kernel is the given equivalence relation. Since all of these canonical preorders are defined in an homogeneous way, we can prove properties for them in a generic way. As an illustrative example of this technique, we generate an axiomatic characterisation of each of these canonical preorders, that is obtained simply by adding a single axiom to the axiomatization of the original equivalence relation. Thus we provide an alternative axiomatization for any axiomatizable preorder in the linear time-branching time spectrum, whose correctness and completeness can be proved once and for all. Although we first prove, by induction, our results for finite processes, then we see, by using continuity arguments, that they are also valid for infinite (finitary) processes

An Integrated Formal Task Specification Method for Smart Environments

This thesis is concerned with the development of interactive systems for smart environments. In such scenario different interaction paradigms need to be supported and according methods and development strategies need to be applied to comprise not only explicit interaction (e.g., pressing a button to adjust the light) but also implicit interactions (e.g., walking to the speaker’s desk to give a talk) to assist the user appropriately. A task-based modeling approach is introduced allowing basing the implementing of different interaction paradigms on the same artifact

Verification in the Hierarchical Development of Reactive Systems

In many approaches to the verification of reactive systems, operational semantics are used to model systems whereas specifications are expressed in temporal logics. Most approaches however fail to handle changes of the specification but assume, that the initial specification is indeed the intended one. Changing the specification thus necessitates to find an accordingly adapted system and to carry out the verification from scratch. During a systems life cycle however, changes of the requirements and resources necessitate repeated adaptations of specifications. We here propose a method that supports syntactic action refinement (in the process algebra TCSP and the Modal Mu-Calculus) and allows to automatically obtain (a priori) correct reactive systems by hierarchically adding details to the according specifications