Uso de riscos na validação de sistemas baseados em componentes

Orientadores: Eliane Martins, Henrique Santos do Carmo MadeiraTese (doutorado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: A sociedade moderna está cada vez mais dependente dos serviços prestados pelos computadores e, conseqüentemente, dependente do software que está sendo executado para prover estes serviços. Considerando a tendência crescente do desenvolvimento de produtos de software utilizando componentes reutilizáveis, a dependabilidade do software, ou seja, a segurança de que o software irá funcionar adequadamente, recai na dependabilidade dos componentes que são integrados. Os componentes são normalmente adquiridos de terceiros ou produzidos por outras equipes de desenvolvimento. Dessa forma, os critérios utilizados na fase de testes dos componentes dificilmente estão disponíveis. A falta desta informação aliada ao fato de se estar utilizando um componente que não foi produzido para o sistema e o ambiente computacional específico faz com que a reutilização de componentes apresente um risco para o sistema que os integra. Estudos tradicionais do risco de um componente de software definem dois fatores que caracteriza o risco, a probabilidade de existir uma falha no componente e o impacto que isso causa no sistema computacional. Este trabalho propõe o uso da análise do risco para selecionar pontos de injeção e monitoração para campanhas de injeção de falhas. Também propõe uma abordagem experimental para a avaliação do risco de um componente para um sistema. Para se estimar a probabilidade de existir uma falha no componente, métricas de software foram combinadas num modelo estatístico. O impacto da manifestação de uma falha no sistema foi estimado experimentalmente utilizando a injeção de falhas. Considerando esta abordagem, a avaliação do risco se torna genérica e repetível embasando-se em medidas bem definidas. Dessa forma, a metodologia pode ser utilizada como um benchmark de componentes quanto ao risco e pode ser utilizada quando é preciso escolher o melhor componente para um sistema computacional, entre os vários componentes que provêem a mesma funcionalidade. Os resultados obtidos na aplicação desta abordagem em estudos de casos nos permitiram escolher o melhor componente, considerando diversos objetivos e necessidades dos usuáriosAbstract: Today's societies have become increasingly dependent on information services. A corollary is that we have also become increasingly dependent on computer software products that provide such services. The increasing tendency of software development to employ reusable components means that software dependability has become even more reliant on the dependability of integrated components. Components are usually acquired from third parties or developed by unknown development teams. In this way, the criteria employed in the testing phase of components-based systems are hardly ever been available. This lack of information, coupled with the use of components that are not specifically developed for a particular system and computational environment, makes components reutilization risky for the integrating system. Traditional studies on the risk of software components suggest that two aspects must be considered when risk assessment tests are performed, namely the probability of residual fault in software component, and the probability of such fault activation and impact on the computational system. The present work proposes the use of risk analysis to select the injection and monitoring points for fault injection campaigns. It also proposes an experimental approach to evaluate the risk a particular component may represent to a system. In order to determine the probability of a residual fault in the component, software metrics are combined in a statistical mode!. The impact of fault activation is estimated using fault injection. Through this experimental approach, risk evaluation becomes replicable and buttressed on well-defined measurements. In this way, the methodology can be used as a components' risk benchmark, and can be employed when it is necessary to choose the most suitable among several functionally-similar components for a particular computational system. The results obtained in the application of this approach to specific case studies allowed us to choose the best component in each case, without jeopardizing the diverse objectives and needs of their usersDoutoradoDoutor em Ciência da Computaçã

Delayed failure of software components using stochastic testing

The present research investigates the delayed failure of software components and addresses the problem that the conventional approach to software testing is unlikely to reveal this type of failure. Delayed failure is defined as a failure that occurs some time after the condition that causes the failure, and is a consequence of long-latency error propagation. This research seeks to close a perceived gap between academic research into software testing and industrial software testing practice by showing that stochastic testing can reveal delayed failure, and supporting this conclusion by a model of error propagation and failure that has been validated by experiment. The focus of the present research is on software components described by a request-response model. Within this conceptual framework, a Markov chain model of error propagation and failure is used to derive the expected delayed failure behaviour of software components. Results from an experimental study of delayed failure of DBMS software components MySQL and Oracle XE using stochastic testing with random generation of SQL are consistent with expected behaviour based on the Markov chain model. Metrics for failure delay and reliability are shown to depend on the characteristics of the chosen experimental profile. SQL mutation is used to generate negative as well as positive test profiles. There appear to be few systematic studies of delayed failure in the software engineering literature, and no studies of stochastic testing related to delayed failure of software components, or specifically to delayed failure of DBMS. Stochastic testing is shown to be an effective technique for revealing delayed failure of software components, as well as a suitable technique for reliability and robustness testing of software components. These results provide a deeper insight into the testing technique and should lead to further research. Stochastic testing could provide a dependability benchmark for component-based software engineering

Performance Implications of Using Diverse Redundancy for Database Replication

Using diverse redundancy for database replication is the focus of this thesis. Traditionally, database replication solutions have been built on the fail-stop failure assumption, i.e. that crashes are believed to cause a majority of failures. However, recent findings refuted this common assumption, showing that many of the faults cause systematic non-crash failures. These findings demonstrate that the existing, non-diverse database replication solutions, which use the same database server products, are ineffective fault-tolerant mechanisms. At the same time, the findings motivated the use of diverse redundancy (when different database server products are used) as a promising way of improving dependability. It seems that using a fault-tolerant server, built with diverse database servers, would deliver improvements in availability and failure rates compared with the individual database servers or their replicated, non-diverse configurations. Besides the potential for improving dependability, one would like to evaluate the performance implications of using diverse redundancy in the context of database replication. This is the focal point of the research. The work performed to that end can be summarised as follows: - We conducted a substantial performance evaluation of database replication using diverse redundancy. We compared its performance to the ones of various non-diverse configurations as well as non-replicated databases. The experiments revealed systematic differences in behaviour of diverse servers. They point to the potential for performance improvement when diverse servers are used. Under particular workloads diverse servers performed better than both non-diverse and non-replicated configurations. - We devised a middleware-based database replication protocol, which provides dependability assurance and guarantees database consistency. It uses an eager update everywhere approach for replica control. Although we focus on the use of diverse database servers, the protocol can be used with the database servers from the same vendor too. We provide the correctness criteria of the protocol. Different regimes of operation of the protocol are defined, which would allow it to be dynamically optimised for either dependability or performance improvements. Additionally, it can be used in conjunction with high-performance replication solutions. - We developed an experimental test harness for performance evaluation of different database replication solutions. It enabled us to evaluate the performance of the diverse database replication protocol, e.g. by comparing it against known replication solutions. We show that, as expected, the improved dependability exhibited by our replication protocol carries a performance overhead. Nevertheless, when optimised for performance improvement our protocol shows good performance. - In order to minimise the performance penalty introduced by the replication we propose a scheme whereby the database server processes are prioritised to deliver performance improvements in cases of low to modest resource utilisation by the database servers. - We performed an uncertainty-explicit assessment of database server products. Using an integrated approach, where both performance and reliability are considered, we rank different database server products to aid selection of the components for the fault-tolerant server built out of diverse databases

Space station data system analysis/architecture study. Task 2: Options development, DR-5. Volume 2: Design options

The primary objective of Task 2 is the development of an information base that will support the conduct of trade studies and provide sufficient data to make key design/programmatic decisions. This includes: (1) the establishment of option categories that are most likely to influence Space Station Data System (SSDS) definition; (2) the identification of preferred options in each category; and (3) the characterization of these options with respect to performance attributes, constraints, cost and risk. This volume contains the options development for the design category. This category comprises alternative structures, configurations and techniques that can be used to develop designs that are responsive to the SSDS requirements. The specific areas discussed are software, including data base management and distributed operating systems; system architecture, including fault tolerance and system growth/automation/autonomy and system interfaces; time management; and system security/privacy. Also discussed are space communications and local area networking

Micro Smart Micro-grid and Its Cyber Security Aspects in a Port Infrastructure

Maritime ports are intensive energy areas with a plenty of electrical systems that require an average power of many tens of megawatts (MW). Competitiveness, profits, reduction of pollution, reliability of operations, carbon emission trading are important energy related considerations for any port authority. Current technology allows the deployment of a local micro-grid of the size of tenths of MW, capable of islanded operation in case of emergency and to grant an increasing energy independency. Ownership of the grid permits a large flexibility on prices of energy sold inside the port, trading on local electric market and reduction of pollution. Renewable energy generation has a large impact on costs since features a low marginal cost. Unfortunately the smart grid is a critical asset within the port infrastructure and its intelligence is a high-level target for cyberattacks. Such attacks are often based on malicious software (malware), which makes use of a controlling entity on the network to coordinate and propagate. In this document, we will outline some features of a port smart grid and typical characteristics of cyber-attacks including potential ways to recognize it and suggestion for effective countermeasures

Design Development Test and Evaluation (DDT and E) Considerations for Safe and Reliable Human Rated Spacecraft Systems

A team directed by the NASA Engineering and Safety Center (NESC) collected methodologies for how best to develop safe and reliable human rated systems and how to identify the drivers that provide the basis for assessing safety and reliability. The team also identified techniques, methodologies, and best practices to assure that NASA can develop safe and reliable human rated systems. The results are drawn from a wide variety of resources, from experts involved with the space program since its inception to the best-practices espoused in contemporary engineering doctrine. This report focuses on safety and reliability considerations and does not duplicate or update any existing references. Neither does it intend to replace existing standards and policy