We present an analysis framework for performance evaluation of large-scale resource-bound (LSRB) computer systems. LSRB systems are those whose resources are continually in demand to serve resource users, who appear in large populations and cause high contention. In these systems, the delivery of quality service is crucial, even in the event of resource failure. Therefore, various techniques have been developed for evaluating their performance. In this thesis, we focus on the technique of quantitative modelling, where in order to study a system, first its model is constructed and then the system’s behaviour is analysed via the model. A number of high level formalisms have been developed to aid the task of model construction. We focus on PEPA, a stochastic process algebra that supports compositionality and enables us to easily build complex LSRB models. In spite of this advantage, however, the task of analysing LSRB models still poses unresolved challenges. LSRB models give rise to very large state spaces. This issue, known as the state space explosion problem, renders the techniques based on discrete state representation, such as numerical Markovian analysis, computationally expensive. Moreover, simulation techniques, such as Gillespie’s stochastic simulation algorithm, are also computationally demanding, as numerous trajectories need to be collected. Furthermore, as we show in our first contribution, the techniques based on the mean-field theory or fluid flow approximation are not readily applicable to this case. In LSRB models, resources are not assumed to be present in large populations and models exhibit highly noisy and stochastic behaviour. Thus, the mean-field deterministic behaviour might not be faithful in capturing the system’s randomness and is potentially too crude to show important aspects of their behaviours. In this case, the modeller is unable to obtain important performance indicators, such as the reliability measures of the system. Considering these limitations, we contribute the following analytical methods particularly tailored to LSRB models. First, we present an aggregation method. The aggregated model captures the evolution of only the system’s resources and allows us to efficiently derive a probability distribution over the configurations they experience. This distribution provides full faithfulness for studying the stochastic behaviour of resources. The aggregation can be applied to all LSRB models that satisfy a syntactic aggregation condition, which can be quickly checked syntactically. We present an algorithm to generate the aggregated model from the original model when this condition is satisfied. Second, we present a procedure to efficiently detect time-scale near-complete decomposability (TSND). The method of TSND allows us to analyse LSRB models at a reduced cost, by dividing their state spaces into loosely coupled blocks. However, one important input is a partition of the transitions defined in the model, categorising them into slow or fast. Forming the necessary partition by the analysis of the model’s complete state space is costly. Our process derives this partition efficiently, by relying on a theorem stating that our aggregation preserves the original model’s partition and therefore, it can be derived by an efficient reachability analysis on the aggregated state space. We also propose a clustering algorithm to implement this reachability analysis. Third, we present the method of conditional moments (MCM) to be used on LSRB models. Using our aggregation, a probability distribution is formed over the configurations of a model’s resources. The MCM outputs the time evolution of the conditional moments of the marginal distribution over resource users given the configurations of resources. Essentially, for each such configuration, we derive measures such as conditional expectation, conditional variance, etc. related to the dynamics of users. This method has a high degree of faithfulness and allows us to capture the impact of the randomness of the behaviour of resources on the users. Finally, we present the advantage of the methods we proposed in the context of a case study, which concerns the performance evaluation of a two-tier wireless network constructed based on the femto-cell macro-cell architecture.

A representação e execução de processos de negócio têm gerado importantes desafios na área de Ciência da Computação. Um desses desafios é a escolha do melhor arcabouço formal para a especificação dos controles de fluxo padrões. Algumas linguagens defendem o uso de redes de Petri ou álgebras de processos como base formal. O uso de redes de Petri para especificar workflows clássicos é uma abordagem bastante conhecida. Entretanto, pesquisas recentes vêm difundindo o uso de novas extensões da álgebra de processos como uma alternativa para a especificação formal de workflows. A principal contribuição deste trabalho é a definição da Navigation Plan Definition Language (NPDL). A NPDL foi implementada como uma extensão da linguagem SQL. Ela é uma alternativa para a representação de workflows que utiliza a álgebra de processos como arcabouço formal. A NPDL promove uma separação explícita entre o ambiente de especificação e o ambiente de execução de um workflow. Esta separação propicia o reaproveitamento de passos de negócio e o uso das propriedades da álgebra de processos não só na modelagem, mas também no controle da execução dos processos. Após a especificação de um workflow por meio da NPDL, a execução dos passos que o definem é controlada pela ferramenta NavigationPlanTool. Essa ferramenta é a segunda contribuição deste trabalho de pesquisa. / The representation and execution of business processes have generated some important challenges in Computer Science. An important related concern is the choosing of the best formal foundation to represent control-flow patterns. Some of the workflow languages advocate the Petri nets or process algebra as formal foundation. The use of Petri nets is a famous approach to support classic workflows. On the other hand some researches are introducing modern process algebra extensions as an alternative formal foundation for representing workflows. The first contribution of this research is the definition of the Navigation Plan Definition Language (NPDL). NPDL was implemented as an extension of SQL language. It is an alternative to represent business processes using process algebra as formal foundation. NPDL provides the explicit separation between specification and execution workflow environment. This separation allows reusing of business steps and usage of process algebra properties in the process modeling and execution controlling tasks. After the definition of a workflow using NPDL, the business steps execution is carried out and controlled by a tool called NavigationPlanTool. This tool is the second contribution of this research.

Recentemente, várias abordagens estão sendo propostas na área de modelagem de processos de negócio. Dentre elas estão as linguagens BPEL e NPDL. BPEL é uma linguagem de representação e execução de processos de negócio que se mostrou bastante expressiva e uma forte candidata a padrão de mercado. NPDL é uma linguagem de definição de processos de negócio baseada em uma extensão de álgebra de processos chamada ACP. NPDL possui uma ferramenta capaz de interpretar e controlar a execução de processos de negócio chamada de NavigationPlanTool. A tradução de processos BPEL para expressões NPDL tem como objetivo fornecer aos processos descritos em BPEL um ambiente de controle e execução baseado em um formalismo algébrico. Entretanto, isso não é uma tarefa fácil. A presença de conceitos em BPEL que não são mapeáveis para NPDL faz com que grande parte da expressividade de BPEL se perca na tradução. Essa perda se dá pela limitação da própria ACP, na qual NPDL se baseia. Para sanar essa dificuldade, surgiu a idéia de estender ou trocar a base algébrica da NPDL. Substituindo a ACP por outro arcabouço algébrico ou incorporando idéias de outras álgebras, seria possível tornar a NPDL mais próxima de BPEL, facilitando, assim, o trabalho de mapeamento. Dentre os arcabouços formais disponíveis, LOTOS tem se mostrado uma interessante alternativa à ACP como base para a NPDL. Para comprovar os benefícios da utilização de conceitos de LOTOS na NPDL ou, até mesmo, de uma troca da base algébrica da NPDL de ACP para LOTOS, este trabalho faz um estudo comparativo entre esses dois formalismos algébricos, buscando encontrar a álgebra com maior expressividade e que represente melhor os conceitos presentes em BPEL. Para essa comparação, serão utilizados os principais conceitos existentes na linguagem BPEL, bem como os Padrões de Controle de Fluxo de Workflow. Não pertence ao escopo deste trabalho a implementação da NPDL usando LOTOS como base formal. / Recently, several approaches are being proposed in the business process modeling area. Among them are BPEL and NPDL languages. BPEL is a business process representation and execution language that has showed itself to be very expressive and a strong candidate to market reference. NPDL is a business process definition language based on a process algebra extension called ACP. NPDL has a tool called NavigationPlanTool that is able to interpret and control the business processes execution. The translation from BPEL processes to NPDL expressions aims to provide to BPEL processes a control and execution environment based on an algebraic foundation. However, this is not an easy task. Due to the translation, the presence of BPEL concepts that can´t be mapped to NPDL results in a heavy BPEL expressiveness loss. This loss occurs by the limitation of ACP, in which NPDL is based on. To solve this problem, the idea of extending or replacing the NPDL algebraic base has appeared. Replacing ACP with other algebraic framework or incorporating ideas from other algebras, could make NPDL closer to BPEL, turning the mapping work easier. Among the formal frameworks available, LOTOS has showed itself an interesting alternative to ACP as an NPDL basis. To prove the benefits of using LOTOS concepts in NPDL, or even exchanging the NPDL algebraic base from ACP to LOTOS, this work presents a comparative study between these two algebraic foundations, trying to find the most expressive algebra and the one that best represents the BPEL concepts. For this comparison, the BPEL main concepts and the Workflow Control-Flow Patterns will be used. The NPDL implementation using LOTOS as formal foundation is out of the scope of this work.

PROCESS algebras are a family of techniques used in formal specification and analysis of computer systems, specially when independent processes that perform and synchronize in parallel are concerned. The so-called concurrent systems. Circus is a process algebra that aggregates the expressiveness power for concurrent behaviors from CSP, along with the predicative data modelling aspects of Z. Recent publications have established a formal exhaustive symbolic testing theory for specifications modelled in Circus. Aiming to improve the feasibility of applying such tests in practical scenarios, it is convenient to look for criteria that reduces the number of test cases which, by the exhaustive nature of the approach, is often infinite. In the light of this, the work we present proposes the application of mutation testing techniques in Circus specifications, targeting the coverage of faults seeded by well-known mutation operators, along with operators designed with the particularities of the language in mind. Some contributions were produced in the pursuit of these goals, such as establishing a formal theory for mutation testing in Circus specifications and the implementation of a symbolic traces generator for the language. / ÁLGEBRAS de processos são uma família de técnicas de especificação e análise formal utilizadas em sistemas computacionais, especialmente em contextos de processos independentes, que atuam paralelamente e efetuam comunicação entre si. São os chamados sistemas concorrentes. Circus é uma álgebra de processos que agrega a capacidade de expressão de comportamentos concorrentes do CSP com a modelagem predicativa de dados da notação Z. Trabalhos recentes vêm estabelecer uma teoria para o teste simbólico exaustivo baseado em especificações modeladas em Circus. Com o objetivo de viabilizar a aplicação prática desses testes, é conveniente estudar critérios que reduzam o conjunto de casos de teste que, pela sua natureza exaustiva, torna-se frequentemente infinito. Neste sentido, o presente trabalho propõe a aplicação de técnicas de teste de mutação à partir de especificações Circus, visando a cobertura de falhas inseridas por meio de operadores de mutação já conhecidos, juntamente com operadores propostos especificamente para a linguagem. Algumas contribuições foram produzidas na busca destes objetivos, como o estabelecimento de uma teoria formal para a aplicação de teste de mutação em especificações Circus e a implementação de um gerador de rastros simbólicos para a mesma linguagem.

A representação e execução de processos de negócio têm gerado importantes desafios na área de Ciência da Computação. Um desses desafios é a escolha do melhor arcabouço formal para a especificação dos controles de fluxo padrões. Algumas linguagens defendem o uso de redes de Petri ou álgebras de processos como base formal. O uso de redes de Petri para especificar workflows clássicos é uma abordagem bastante conhecida. Entretanto, pesquisas recentes vêm difundindo o uso de novas extensões da álgebra de processos como uma alternativa para a especificação formal de workflows. A principal contribuição deste trabalho é a definição da Navigation Plan Definition Language (NPDL). A NPDL foi implementada como uma extensão da linguagem SQL. Ela é uma alternativa para a representação de workflows que utiliza a álgebra de processos como arcabouço formal. A NPDL promove uma separação explícita entre o ambiente de especificação e o ambiente de execução de um workflow. Esta separação propicia o reaproveitamento de passos de negócio e o uso das propriedades da álgebra de processos não só na modelagem, mas também no controle da execução dos processos. Após a especificação de um workflow por meio da NPDL, a execução dos passos que o definem é controlada pela ferramenta NavigationPlanTool. Essa ferramenta é a segunda contribuição deste trabalho de pesquisa. / The representation and execution of business processes have generated some important challenges in Computer Science. An important related concern is the choosing of the best formal foundation to represent control-flow patterns. Some of the workflow languages advocate the Petri nets or process algebra as formal foundation. The use of Petri nets is a famous approach to support classic workflows. On the other hand some researches are introducing modern process algebra extensions as an alternative formal foundation for representing workflows. The first contribution of this research is the definition of the Navigation Plan Definition Language (NPDL). NPDL was implemented as an extension of SQL language. It is an alternative to represent business processes using process algebra as formal foundation. NPDL provides the explicit separation between specification and execution workflow environment. This separation allows reusing of business steps and usage of process algebra properties in the process modeling and execution controlling tasks. After the definition of a workflow using NPDL, the business steps execution is carried out and controlled by a tool called NavigationPlanTool. This tool is the second contribution of this research.

A hybrid system is a system that presents both continuous time evolution and discrete events. To define and analyse such systems prior to building actual products, a hybrid process algebra can be employed. Simulation is often used as a convenient way for a better understanding of the systems’ evolution and its potential weaknesses. This study aims at creating a general architecture of the simulation tool for hybrid process algebras, together with a practical implementation of Behavioural Hybrid Process Calculus simulator. For achieving this objective, a list of tasks has been composed, including the analysis of several hybrid process algebra operators, development of an easily extendible architecture of the tool, the definition of the input language, capable of describing BHPC processes, and a programming solution of the simulator. Together with a simulator tool, a programming solution for the visualisation of hybrid systems’ evolution is created and presented. The application uses Message Sequence Plots diagrams to represent such evolution, which allows a convenient overview and analysis for most of hybrid system simulations. The currently developed simulation and visualisation tools may be regarded as a working ground for both the usage and further development. The improvement points of the tools should be constantly collected from the user experience and implemented. The long term goal of the work is to achieve an expanding community with the joint effort to create a... [to full text] / Hibridinė sistema yra sistema, sudaryta iš laike tolydžios evoliucijos ir diskrečių įvykių. Hibridinių procesų algebros pagalba tokias sistemas galima apibrėžti ir analizuoti dar prieš sukuriant galutinį produktą. Tuo tarpu simuliacija yra dažnai naudojama kaip patogus būdas geresniam sistemos evoliucijos suvokimui ir jos potencialių silpnybių identifikavimui. Šiuo darbu siekiama sukurti bendrą architektūrą hibridinių procesų algebrų simuliavimo įrankiui bei sukurti praktinę priemonę – simuliatorių, skirtą Elgsenos Hibridinių Procesų Algebrai (angl. Behavioural Hybrid Process Calculus – BHPC). Siekiant įgyvendinti šį tikslą, buvo sudarytas užduočių sąrašas, įtraukiant į jį kelių hibridinių procesų algebrų operatorių analizę, nesudėtingai plečiamos programos architektūros sukūrimą, įvedimo kalbos, gebančios aprašyti BHPC procesus, apibrėžimą bei programinio simuliatoriaus sprendimo įgyvendinimą. Hibridinių sistemų evoliucijos vaizdavimui buvo sukurtas programinis sprendimas, naudojantis Pranešimų Sekos Grafiko (angl. Message Sequence Plots) vaizdavimo tipą grafiniam hibridinės evoliucijos atvaizdavimui, kuris suteikia galimybę patogiai apžvelgti ir analizuoti daugumą hibridinių sistemų evoliucijų. Šiuo metu sukurti simuliavimo ir vaizdavimo įrankiai gali būti naudojami praktikoje, tuo pačiu renkant vartotojų patirtį tolesniam jų tobulinimui. Įrankių tobulinimo aspektai turėtų būti nuolatos kaupiami ir įgyvendinami siekiant ilgalaikio šio darbo tikslo – suburti augančią... [toliau žr. visą tekstą]

Mobility occurs naturally in many distributed system applications such as telecommunications and electronic commerce. Mobility may reduce bandwidth consumption and coupling and increase flexibility. However, it seems that relatively little work has been done to support quality assurance techniques such as testing and verification of mobile systems. This thesis describes an approach for checking the conformance of a mobile, distributed application with respect to an executable model at runtime. The approach is based on kiltera -- a novel, high-level language supporting the description and execution of models of concurrent, mobile, distributed, and timed computation. The approach allows distributed, rather than centralized, monitoring. However, it makes very few assumptions about the platform that the mobile agent system is implemented in. We have implemented our approach and validated it using four case studies. Two of them are examples of mobile agent systems, the two others are implementations of distributed algorithms. Our approach was able to detect seeded faults in the implementations. To check the effectiveness and the efficiency of our approach more comprehensively a mutation-based evaluation framework has been implemented. In this framework a set of a new mutation operators for mobile agent systems has been identified in order to automatically generate and run a number of mutants programs and then evaluate the ability of our approach to detect these mutants. We found that our approach is very effective and efficient in killing the non-equivalent mutants. / Thesis (Ph.D, Computing) -- Queen's University, 2010-04-27 12:35:47.996

Recentemente, várias abordagens estão sendo propostas na área de modelagem de processos de negócio. Dentre elas estão as linguagens BPEL e NPDL. BPEL é uma linguagem de representação e execução de processos de negócio que se mostrou bastante expressiva e uma forte candidata a padrão de mercado. NPDL é uma linguagem de definição de processos de negócio baseada em uma extensão de álgebra de processos chamada ACP. NPDL possui uma ferramenta capaz de interpretar e controlar a execução de processos de negócio chamada de NavigationPlanTool. A tradução de processos BPEL para expressões NPDL tem como objetivo fornecer aos processos descritos em BPEL um ambiente de controle e execução baseado em um formalismo algébrico. Entretanto, isso não é uma tarefa fácil. A presença de conceitos em BPEL que não são mapeáveis para NPDL faz com que grande parte da expressividade de BPEL se perca na tradução. Essa perda se dá pela limitação da própria ACP, na qual NPDL se baseia. Para sanar essa dificuldade, surgiu a idéia de estender ou trocar a base algébrica da NPDL. Substituindo a ACP por outro arcabouço algébrico ou incorporando idéias de outras álgebras, seria possível tornar a NPDL mais próxima de BPEL, facilitando, assim, o trabalho de mapeamento. Dentre os arcabouços formais disponíveis, LOTOS tem se mostrado uma interessante alternativa à ACP como base para a NPDL. Para comprovar os benefícios da utilização de conceitos de LOTOS na NPDL ou, até mesmo, de uma troca da base algébrica da NPDL de ACP para LOTOS, este trabalho faz um estudo comparativo entre esses dois formalismos algébricos, buscando encontrar a álgebra com maior expressividade e que represente melhor os conceitos presentes em BPEL. Para essa comparação, serão utilizados os principais conceitos existentes na linguagem BPEL, bem como os Padrões de Controle de Fluxo de Workflow. Não pertence ao escopo deste trabalho a implementação da NPDL usando LOTOS como base formal. / Recently, several approaches are being proposed in the business process modeling area. Among them are BPEL and NPDL languages. BPEL is a business process representation and execution language that has showed itself to be very expressive and a strong candidate to market reference. NPDL is a business process definition language based on a process algebra extension called ACP. NPDL has a tool called NavigationPlanTool that is able to interpret and control the business processes execution. The translation from BPEL processes to NPDL expressions aims to provide to BPEL processes a control and execution environment based on an algebraic foundation. However, this is not an easy task. Due to the translation, the presence of BPEL concepts that can´t be mapped to NPDL results in a heavy BPEL expressiveness loss. This loss occurs by the limitation of ACP, in which NPDL is based on. To solve this problem, the idea of extending or replacing the NPDL algebraic base has appeared. Replacing ACP with other algebraic framework or incorporating ideas from other algebras, could make NPDL closer to BPEL, turning the mapping work easier. Among the formal frameworks available, LOTOS has showed itself an interesting alternative to ACP as an NPDL basis. To prove the benefits of using LOTOS concepts in NPDL, or even exchanging the NPDL algebraic base from ACP to LOTOS, this work presents a comparative study between these two algebraic foundations, trying to find the most expressive algebra and the one that best represents the BPEL concepts. For this comparison, the BPEL main concepts and the Workflow Control-Flow Patterns will be used. The NPDL implementation using LOTOS as formal foundation is out of the scope of this work.

Abstract Due to increasing amount of concurrency, systems have become difficult to design and analyse. In this effort, formal verification, which means proving the correctness of a system, has turned out to be useful. Unfortunately, the application domain of the formal verification methods is often indefinite, tools are typically unavailable, and most of the techniques do not suit especially well for the verification of software systems. These are the questions addressed in the thesis. A typical approach to modelling systems and specifications is to consider them parameterised by the restrictions of the execution environment, which results in an (infinite) family of finite-state verification tasks. The thesis introduces a novel approach to the verification of such infinite specification-system families represented as labelled transition systems (LTSs). The key idea is to exploit the algebraic properties of the correctness relation. They allow the correctness of large system instances to be derived from that of smaller ones and, in the best case, an infinite family of finite-state verification tasks to be reduced to a finite one, which can then be solved using existing tools. The main contribution of the thesis is an algorithm that automates the reduction method. A specification and a system are given as parameterised LTSs and the allowed parameter values are encoded using first order logic. Parameters are sets and relations over these sets, which are typically used to denote, respectively, identities of replicated components and relationships between them. Because the number of parameters is not limited and they can be nested as well, one can express multiply parameterised systems with a parameterised substructure, which is an essential property from the viewpoint of modelling software systems. The algorithm terminates on all inputs, so its application domain is explicit in this sense. Other proposed parameterised verification methods do not have both these features. Moreover, some of the earlier results on the verification of parameterised systems are obtained as a special case of the results presented here. Finally, several natural and significant extensions to the formalism are considered, and it is shown that the problem becomes undecidable in each of the cases. Therefore, the algorithm cannot be significantly extended in any direction without simultaneously restricting some other aspect.

Multi-scale modelling and analysis is becoming increasingly important and relevant. Analysis of the emergent properties from the interactions between scales of multi-scale systems is important to aid in solutions. There is no universally adopted theoretical/computational framework or language for the construction of multi-scale models. Most modelling approaches are specific to the problem that they are addressing and use a hybrid combination of modelling languages to model specific scales. This thesis addresses if process algebra can offer a unique opportunity in the definition and analysis of multi-scale models. In this thesis the generic Process Algebra with Layers (PAL) is defined: a language for multi-scale integration modelling. This work highlights the potential of process algebra to model multi-scale systems. PAL was designed based on features and challenges found from modelling a multi-scale system in an existing process algebra. The unique features of PAL are the layers: Population and Organism. The novel language modularises the spatial scales of the system into layers, therefore, modularising the detail of each scale. An Organism can represent a molecule, organelle, cell, tissue, organ or any organism. An Organism is described by internal species. An internal species, dependent on the scale of the Organism, can also represent a molecule, organelle, cell, tissue, organ or any organism. Populations hold specific types of Organism, for example, life stages, cell phases, infectious states and many more. The Population and Organism layers are integrated through mirrored actions. This novel language allows the clear definition of scales and interactions within and between these scales in one model. PAL can be applied to define a variety of multi-scale systems. PAL has been applied to two unrelated multi-scale system case studies to highlight the advantages of the generic novel language. Firstly the effects of ocean acidification on the life stages of the Pacific oyster. Secondly the effects of DNA damage from cancer treatment on the length of a cell cycle and cell population growth.