Web Service Interfaces: Design, Trends and Model Driven Engineering

Abstract

A luxury of the recent past, the ubiquitous Internet, has now become a necessity. The necessity of being connected to internet, especially with the advent of smart devices and internet-of-things solutions, implies that modern software applications are no more the isolated systems of the past. Software systems are now built to communicate, and web services have simplified this communication by limiting outside application access to a particular set of features. The interface of a web service, also known as the API (Application Programming Interface), precisely defines how an application would talk to the rest of the digital world, while hiding the intricate implementation details of the backend. The fact that a service interface is the only available gateway to a web service, makes it an important constituent of any service oriented activity. This thesis addresses challenges for using service interface descriptions in end-to-end model-driven service oriented applications. The first challenge is related to service interface design. Interface description of the classic web services, WSDL, has extensively been used in research and development activities for over a decade. However, the requirements of modern service applications, and the recent proliferation of XaaS (Everything as a Service) architectures, have introduced several new types of services and many formats to describe their interfaces. Unlike WSDL, the newer breeds of service interfaces are not based on specific standards, which has resulted in a huge heterogeneity among their design practices and patterns. Therefore, it is crucial to understand the evolution and challenges of the emerging, heterogeneously designed service interfaces before using them in any service oriented activity. As a contribution, we performed a thorough analysis of more than eleven thousand publicly available API descriptions, across eight formats, taken from multiple repositories on the Internet, and provided conclusions by examining different elements used to design and describe the services. The study not only helps in understanding the common interface design patterns and evolving trends in modern service oriented architecture, but also evaluates the community-proposed design practices for APIs. The second challenge we address is to automatically model a service behavior using its interface description. Behavioral modeling is a common, intermediate step of several service oriented operations, so automatically deriving service behavior from an API can provide an automatic, end-to-end solution for a variety of service oriented activities including service discovery, service validation, and execution monitoring. In contrast to existing approaches, our proposed technique emphasizes on using certain elements of a standard interface description, without making alterations to its structure. Automatic modeling also eliminates the need for informal documentation, which characterizes current practices, and which would otherwise be required to design formal behavioral models. Finally, using our auto-generated behavioral models, we propose a framework for automatic service composition, addressing the functional requirements and data mediation among the participating services, in a unified manner. Our formal approach is based on model checking, where web service behaviors are modeled as Synchronous Kripke Structure, while the desired functional behavior or control flow is specified with the help of Computation Tree Logic properties. To conclude, the three-fold contributions of this thesis are driven by service inter-faces, and provide the essential ingredients for design-first approaches for service-oriented research and development activities. The proposed design recommendations, automatic behavioral modeling algorithm, and data mismatch solution for a practical service composition application, can fill in the missing pieces of puzzle at many places, and in any desired combination.