Microservices expose their functionality via remote Application Programming Interfaces (APIs), e.g., based on HTTP or asynchronous messaging technology. To solve recurring problems in this design space, Microservice API Patterns (MAPs) have emerged to capture the collective experience of the API design community. At present, there is a lack of empirical evidence for the effectiveness of these patterns, e.g., how they impact understandability and API usability. We therefore conducted a controlled experiment with 6 microservice patterns to evaluate their impact on understandability with 65 diverse participants. Additionally, we wanted to study how demographics like years of professional experience or experience with MAPs influence the effects of the patterns. Per pattern, we constructed two API examples, each in a pattern version P and a functionally equivalent non-pattern version N (24 in total). Based on a crossover design, participants had to answer comprehension Questions, while we measured the time. For five of the six patterns, we identified a significant positive impact on understandability, i.e., participants answered faster and / or more correctly for P. However, effect sizes were mostly small, with one pattern showing a medium effect. The correlations between performance and demographics seem to suggest that certain patterns may introduce additional complexity; people experienced with MAPs will profit more from their effects. This has important implications for training and education around MAPs and other patterns.

In contemporary software engineering, business value and end user requirements are the primary drivers for design decisions. Ethical values such as fairness and sustainability, a key concern in green software engineering, are complementary, non-technical drivers addressed by value-based systems engineering as, for instance, specified in IEEE Standard 7000. Such process-centric initiatives explain what should be done but not how to get there. Practitioners are assumed to be able and willing to locate documents such as codes of conduct; document study is required ("pull"). A proactive, lightweight integration into existing agile practices, providing tangible on-the-job advice for developers and other stakeholders, is missing ("push"). Our research agenda addresses this problem area. Following a proactive approach, we propose to combine existing work to ease access to and consumption of ethical and green design knowledge for a world in which software systems are increasingly no longer passive tools for users but make autonomous decisions affecting human lives and the planet. In this short paper, we report on a completed and two emerging projects in this topic area in terms of their goals, preliminary results, and envisioned future work.

Microservice API design is a critical aspect in crafting a microservice architecture. While API design in general has been studied, the specific relation of API design to design practices and models commonly used in microservice architectures is yet understudied. In particular, practitioners frequently use Domain-Driven Design (DDD) in their microservice architecture and API designs. We thus decided to study existing Architectural Design Decisions (ADDs), their solutions options, their relations, and the decision drivers in these decisions. Using the Grounded Theory research method we studied grey literature sources. In this study, we identified six ADDs with 27 decision options, numerous relations between them, and 27 decision drivers. The decisions cover mapping domain models to APIs, defining API contracts in relation to domain models, designing API resources based on domain model elements, segregation of API resources, mapping domain model links to the API, and designing the operations of an API resource.

To make good architecture design decisions, developers need to know suitable architecture solution alternatives. However, with the rapid and continuous increase of solution alternatives (e.g. technologies, patterns, tactics), it is challenging to acquire architecture knowledge and to ensure that this knowledge is up to date. Our goal is to improve how architects search for architecturally relevant information in online developer communities. We developed a new search approach for architecturally relevant information using Stack Overflow as an example of an online developer community. Our search approach differs from a conventional keyword-based search in that it considers semantic information of architecturally relevant concepts in Stack Overflow. We also implemented the search approach as a web-based search engine. To show the effectiveness of the search approach compared to a conventional keyword-based search, we conducted an experiment with 16 practitioners. To ensure realism of the experiment, tasks given to practitioners are based on real scenarios identified in interviews with a different set of practitioners. The experiment showed that the new search approach outperforms a conventional keyword based search.

A cloud is a distributed Internet-based software system providing resources as tiered services. Through service-orientation and virtualization for resource provisioning, cloud applications can be deployed and managed dynamically. We discuss the building blocks of an architectural style for cloud-based software systems. We capture style-defining architectural principles and patterns for control-theoretic, model-based architectures for cloud software. While service orientation is agreed on in the form of service-oriented architecture and microservices, challenges resulting from multi-tiered, distributed and heterogeneous cloud architectures cause uncertainty that has not been sufficiently addressed. We define principles and patterns needed for effective development and operation of adaptive cloud-native systems.

Architectural Knowledge Management (AKM) has been a major topic in software architecture research since 2004. Open AKM problems include an effective, seamless transition from reusable knowledge found in patterns books and technology blogs to project-specific decision guidance and an efficient, practical approach to knowledge application and maintenance. We extended our previous work with concepts for problem space modeling, focusing on reusable knowledge, as well as solution space management, focusing on project-level decisions. We implemented these concepts in ADMentor, an extension of Sparx Enterprise Architect. AD Mentor features rapid problem space modeling, UML model linkage, question-option-criteria diagram support, meta-information for model tailoring, as well as decision backlog management. We validated ADMentor by modeling and applying 85 cloud application design decisions and 75 workflow management decisions, creating one problem and three sample solution spaces covering control system architectures, and obtaining user feedback on tool and model content.

Capturing and sharing design knowledge such as architectural decisions is becoming increasingly important in professional Information Technology (IT) services firms. Methods, models, and tools supporting explicit knowledge management strategies have been proposed in recent years. In this paper, we extend previous work in the architectural knowledge management community to satisfy the requirements of an additional user group: the designers of IT infrastructure solutions that are outsourced from one company to another. Such strategic outsourcing solutions require complex, contractually relevant design decisions concerning many different resources such as IT infrastructures, people, and real estate. In this paper, we present a reference architecture and a decision process-oriented knowledge metamodel that we synthesized from the domain-specific functional requirements and quality attributes. We also present a tool implementation of these decision modeling concepts and discuss user feedback.

When constructing software systems, software architects must identify and evaluate many competing design options and document the rationale behind any selections made. Two supporting concepts are pattern languages and architectural decision models. Unfortunately, both concepts only provide partial support: Extensive upfront education is needed for practitioners to be in command of' the full pattern literature relevant in their field; retrospective architectural decision modeling is viewed as a painful extra responsibility without immediate gains. In this paper, we combine pattern languages and reusable architectural decision models into a design method that is both comprehensive and comprehensible. Our design method identifies the required decisions in requirements models systematically, gives domain-specific pattern selection advice, and provides traceability from platform-independent patterns to platform-specific decisions. We validate our approach by applying it to enterprise applications as an exemplary application genre and a SOA case study from the finance industry.

Recent technology trends in the Web Services (WS) domain indicate that a solution eliminating the presumed complexity of the WS-* standards may be in sight: advocates of REpresentational State Transfer (REST) have come to believe that their ideas explaining why the World Wide Web works are just as applicable to solve enterprise application integration problems and to simplify the plumbing required to build service-oriented architectures. In this paper we objectify the WS-* vs. REST debate by giving a quantitative technical comparison based on architectural principles and decisions. We show that the two approaches differ in the number of architectural decisions that must be made and in the number of available alternatives. This discrepancy between freedom-from-choice and freedom-of-choice explains the complexity difference perceived. However, we also show that there are significant differences in the consequences of certain decisions in terms of resulting development and maintenance costs. Our comparison helps technical decision makers to assess the two integration styles and technologies more objectively and select the one that best fits their needs: REST is well suited for basic, ad hoc integration scenarios, WS-* is more flexible and addresses advanced quality of service requirements commonly occurring in enterprise computing.

Perspectives on Web Services—Applying SOAP, WSDL and UDDIto Real-World Projects O. Zimmermann, M. Tomlinson and S. Peuser . Springer Verlag (2003 ). ISBN 3-540-00914-0. £34.50 /€48.10 . 650 Hardbound