Value- and debt-aware selection and composition in cloud-based service-oriented architectures using real options

This thesis presents a novel model for service selection and composition in Cloud-based Service-Oriented Architectures (CB-SOA), which is called CloudMTD, using real options, Dependency Structure Matrix (DSM) and propagation-cost metrics. CB-SOA architectures are composed of web services, which are leased or bought off the cloud marketplace. CB-SOA can improve its utility and add value to its composition by substituting its constituent services. The substitution decisions may introduce technical debt, which needs to be managed. The thesis defines the concept of technical debt for CB-SOA and reports on the available technical debt definitions and approaches in the literature. The formulation of service substitution problem and its technical debt valuation is based on options, which exploits Binomial Options Analysis. This thesis looks at different option types under uncertainty. This thesis is concerned with some scenarios that may lead to technical debt, which are related to web service selection and composition that has been driven by either a technical or a business objective. In each scenario, we are interested in three decisions (1) keep, (2) substitute or (3) abandon the current service. Each scenario takes into consideration either one or more QoS attribute dimension (e.g. Availability). We address these scenarios from an option-based perspective. Each scenario is linked to a suitable option type. A specific option type depends on the nature of the application, problem to be investigated, and the decision to be taken. In addition, we use Dependency Structure Matrix (DSM) in order to represent dependencies among web services in CB-SOA. We introduce time and complexity sensitive propagation-cost metrics to DSM to solve the problem. In addition, CloudMTD model informs the time-value of the decisions under uncertainty based on behavioral and structural aspects of CB-SOA

Kollaboratives Reengineering und Modularisieren von Softwaresystemen

Software systems evolve over their lifetime. Changing requirements make it inevitable for developers to modify and extend the underlying code base. Specific requirements emerge in the context of open source software where everybody can contribute and requirements can change over time. In particular, research software is often not structured with a maintainable and extensible architecture. Furthermore, often databases are employed for retrieving, storing, and processing application data. Insufficient knowledge of the actual structure and behavior of such software systems and related databases can entail further challenges. Thus, understanding these software systems embodies a crucial task, which needs to be addressed in an appropriate way to face inevitable challenges while performing software changes. Approaches based on alternative display and interaction concepts can support this task by offering a more immersive user experience. In this thesis, we introduce three complementary approaches to support the evolution and particularly understanding of software systems in different aspects. Our main contributions are (i) an approach named CORAL for enabling collaborative reengineering and modularization of software systems, (ii) a gesture-based, collaborative, and multi-user-featuring Virtual Reality approach named ExplorViz VR for the software city metaphor, and (iii) a database behavior live-visualization approach named RACCOON for database comprehension of software systems. An extensive case study shows that our CORAL approach is capable of supporting reengineering and modularization processes. Furthermore, several lab experiments demonstrate the high usability, and efficiency and effectiveness for solving comprehension tasks when using the visualization within our multi-user VR approach ExplorViz VR. All implementations are available as open-source software on www.explorviz.net. Additionally, we provide an extensive experimental package of our latest VR evaluation to facilitate the verifiability and reproducibility of our results

Managing risks and opportunities in cyber-physical systems with software architecture assessments

Peer reviewe

Synergizing domain expertise with self-awareness in software systems:a patternized architecture guideline

To promote engineering self-aware and self-adaptive software systems in a reusable manner, architectural patterns and the related methodology provide an unified solution to handle the recurring problems in the engineering process. However, in existing patterns and methods, domain knowledge and engineers' expertise that is built over time are not explicitly linked to the self-aware processes. This linkage is important, as the knowledge is a valuable asset for the related problems and its absence would cause unnecessary overhead, possibly misleading results and unwise waste of the tremendous benefit that could have been brought by the domain expertise. This paper highlights the importance of synergizing domain expertise and the self-awareness to enable better self-adaptation in software systems, relying on well-defined expertise representation, algorithms and techniques. In particular, we present a holistic framework of notions, enriched patterns and methodology, dubbed DBASES, that offers a principled guideline for the engineers to perform difficulty and benefit analysis on possible synergies, in an attempt to keep "engineers-in-the-loop". Through three tutorial case studies, we demonstrate how DBASES can be applied in different domains, within which a carefully selected set of candidates with different synergies can be used for quantitative investigation, providing more informed decisions of the design choices.Comment: Accepted manuscript to the Proceedings of the IEEE. Please use the following citation: Tao Chen, Rami Bahsoon, and Xin Yao. 2020. Synergizing Domain Expertise with Self-Awareness in Software Systems: A Patternized Architecture Guideline. Proc. IEEE, in pres

Reactive Microservices - An Experiment

Os microserviços são geralmente adotados quando a escalabilidade e flexibilidade de uma aplicação são essenciais para o seu sucesso. Apesar disto, as dependências entre serviços transmitidos através de protocolos síncronos, resultam numa única falha que pode afetar múltiplos microserviços. A adoção da capacidade de resposta numa arquitetura baseada em microserviços, através da reatividade, pode facilitar e minimizar a proliferação de erros entre serviços e na comunicação entre eles, ao dar prioridade à capacidade de resposta e à resiliência de um serviço. Esta dissertação fornece uma visão geral do estado da arte dos microserviços reativos, estruturada através de um processo de mapeamento sistemático, onde são analisados os seus atributos de qualidade mais importantes, os seus erros mais comuns, as métricas mais adequadas para a sua avaliação, e as frameworks mais relevantes. Com a informação recolhida, é apresentado o valor deste trabalho, onde a decisão do projeto e a framework a utilizar são tomadas, através da técnica de preferência de ordem por semelhança com a solução ideal e o processo de hierarquia analítica, respetivamente. Em seguida, é realizada a análise e o desenho da solução, para o respetivo projeto, onde se destacam as alterações arquiteturais necessárias para o converter num projeto de microserviços reativo. Em seguida, descreve-se a implementação da solução, começando pela configuração do projeto necessária para agilizar o processo de desenvolvimento, seguida dos principais detalhes de implementação utilizados para assegurar a reatividade e como a framework apoia e simplifica a sua implementação, finalizada pela configuração das ferramentas de métricas no projeto para apoiar os testes e a avaliação da solução. Em seguida, a validação da solução é investigada e executada com base na abordagem Goals, Questions, Metrics (GQM), para estruturar a sua análise relativamente à manutenção, escalabilidade, desempenho, testabilidade, disponibilidade, monitorabilidade e segurança, finalizada pela conclusão do trabalho global realizado, onde são listadas as contribuições, ameaças à validade e possíveis trabalhos futuros.Microservices are generally adopted when the scalability and flexibility of an application are essential to its success. Despite this, dependencies between services transmitted through synchronous protocols result in one failure, potentially affecting multiple microservices. The adoption of responsiveness in a microservices-based architecture, through reactivity, can facilitate and minimize the proliferation of errors between services and in the communication between them by prioritizing the responsiveness and resilience of a service. This dissertation provides an overview of the reactive microservices state of the art, structured through a systematic mapping process, where its most important quality attributes, pitfalls, metrics, and most relevant frameworks are analysed. With the gathered information, the value of this work is presented, where the project and framework decision are made through the technique of order preference by similarity to the ideal solution and the analytic hierarchy process, respectively. Then, the analysis and design of the solution are idealized for the respective project, where the necessary architectural changes are highlighted to convert it to a reactive microservices project. Next, the solution implementation is described, starting with the necessary project setup to speed up the development process, followed by the key implementation details employed to ensure reactivity and how the framework streamlines its implementation, finalized by the metrics tools setup in the project to support the testing and evaluation of the solution. Then, the solution validation is traced and executed based on the Goals, Questions, Metrics (GQM) approach to structure its analysis regarding maintainability, scalability, performance, testability, availability, monitorability, and security, finalized by the conclusion of the overall work done, where the contributions, threats to validity and possible future work are listed

Towards A Comprehensive Cloud Decision Framework with Financial Viability Assessment

Most organizations moving their legacy systems to the cloud base their decisions on the naïve assumption that the public cloud provides cost savings. However, this is not always true. Sometimes the migration complexity of certain applications outweighs the benefits to be had from a public cloud. Moreover, the total cost of ownership does not necessarily decrease by moving to a public cloud. Therefore, there is a need for a disciplined approach for choosing the right cloud platform for application migration. In this paper, we propose a comprehensive cloud decision framework that includes an extensible decision criteria set, associated usage guidelines, a decision model for cloud platform recommendation, and a cost calculator to compute the total cost of ownership (TCO). The decision process works as follows. It begins with the ordering of relevant criteria, either according to industry best practice or the enterprise’s specific requirements and preferences. A technical recommendation is made on the basis of the criteria classification, which is then assessed for financial viability. By providing traceability of the cost items in the public/private TCO calculators to the decision criteria, the framework enables users to iterate through the decision process, determining and eliminating (if possible) the main cost drivers until a right balance is found between the desirable criteria and the available budget. We illustrate the need, benefits and value of our proposed framework through three different real-world use case scenarios

Cloud Architecture Evaluation

Cloud computing has introduced numerous ways to build software systems in the cloud environment. The complexity of today’s system architectures require architecture evaluation in the designing phase of the system, in the implementation phase, and in the maintenance phase. There are many different architecture evaluation models. This thesis discusses three different evaluation models: architecture tradeoff analysis method, cost-benefit analysis method, and AWS Well-Architected framework. The AWS Well-Architected framework is deeply evaluated by performing an architectural evaluation for the case study software: Lixani 5. This thesis introduces and compares the opportunities for cloud architecture evaluation by literature review, case study, and interviews with experts. The thesis begins with introduction to cloud computing, cloud architecture models and architecture evaluation methods. An architecture evaluation for a case study software is then carried out. This thesis also contains interviews with experts, producing knowledge on how the system architecture is being evaluated in the field. The research methods used in the thesis are literature review, case study, and expert interviews. This thesis attempts to describe and assess the architecture evaluation models by using the research methods. In addition, this thesis introduces and discusses the case study software – Lixani 5 – and its architectural decisions. Based on research in the thesis it was noted that all three studied software architecture evaluation models are suitable options for reviewing software architecture. All models included positive and negative aspects and none of them was seen as superior compared to the others. Based on the interviews with experts it was noted that there are also multiple other efficient ways to evaluate the system architecture than the models discussed in the thesis. These ways included a technology audit template and a proof-of-concept culture