Service Composition in Dynamic Environments: From Theory to Practice

Abstract

In recent years, service-oriented architecture (SOA) has become one of the leading paradigms in software design. Among the key advantages behind SOA is service composition, the ability to create new services by reusing the functionality of pre-existing ones. Despite the availability of standard languages and related design and development tools, ``manual'' service composition remains to be an extremely error-prone and time-consuming task. No surprise, the automation of service composition process has been and still is a hot topic in the area of service computing. In addition to high complexity, modern service-based systems tend to be dynamic. The most common examples of dynamic factors are constantly evolving set of available services, volatile execution context, frequent revision of business policies, regulations and goals, etc. Since dynamic changes of the execution environment can invalidate service compositions predefined within a service-based system, the cost of software maintenance in this case may increase dramatically. Unfortunately, the existing automated service composition approaches are not of much help here. Being design-time by their nature, they intensively involve IT experts, especially for analysing the changes and respecifying formal composition requirements in new conditions, which is still a considerable effort. To make service-based systems more agile, a new composition approach is needed that could automatically perform all composition-related tasks at run time, from deriving composition requirements to generating new compositions to deploying them. In this dissertation, we propose a novel service composition framework that (i) handles stateful and nondeterministic services that interact asynchronously, (ii) allows for rich control- and data-flow composition requirements that are independent from the details of service implementations (iii) exploits advanced planning techniques for automated reasoning and (iv) exploits modeling methodology that is applicable in dynamic environment. The corner stone of the framework is the explicit context model that abstracts composition requirements and constraints away from the details of service implementations. By linking services to the context model on the one side, and by expressing composition requirements and constraints in terms of the context model on the other side, we create a formal setting in which abstract requirements and constraints, though being implementation-independent, can always be grounded to available service implementations. Consequently, we show that in such framework it is possible to move most human activities to design time so that the run-time management of the composition life cycle is completely automated. To the best of our knowledge, it is the first composition approach to achieve this goal. A significant contribution of the dissertation is the investigation of the problem of dynamic adaptation of service-based business processes. Here, our solution is based on the composition approach proposed. Within the thesis, the problem of process adaptation plays the role of the key motivator and evaluation use case for our composition-related research. The most part of the ideas discussed in the thesis are implemented and evaluated to prove their practical applicability.