Abstract. Representational State Transfer (REST) services are gaining momentum as a lightweight approach for the provision of services on the Web. Unlike WSDL-based services, in REST the set of operations is reduced, standardized, with well known semantics, and changes the resource's state. Few attempts have been proposed to support composition models for REST, they are mainly operation-centric and fail to acknowledge the hypermedia nature of REST, that is, clients must inspect the served resource state and choose the link to follow from there. We explore RESTful service composition as it is driven by the hypermedia net that is dynamically created while a client interacts with a server resulting in a light-weight approach. We based our proposal on a hypermedia-centric REST service description, the Resource Linking Language (ReLL) and Petri Nets as a mechanism for describing the machine-client navigation.
The REST architectural style has attracted a lot of interest from industry due to the nonfunctional properties it contributes to Web-based solutions. SOAP/WSDL-based services, on the other hand, provide tools and methodologies that allow the design and development of software supporting complex service arrangements, enabling complex business processes which make use of well-known control-flow patterns. It is not clear if and how such patterns should be modeled, considering RESTful Web services that comply with the statelessness, uniform interface and hypermedia constraints. In this article, we analyze a set of fundamental control-flow patterns in the context of stateless compositions of RESTful services. We propose a means of enabling their implementation using the HTTP protocol and discuss the impact of our design choices according to key REST architectural principles. We hope to shed new light on the design of basic building blocks for RESTful business processes.
The Representational State Transfer (REST) style has become a popular approach for lightweight implementation of Web services, mainly because of relevant benefits such as massive scalability, high evolvability, and low coupling. It was designed considering the humanuser as the one who drives service invocation and discovery. Attempts to provide machine-clients a similar autonomy have been proposed and recently, interesting discussion evaluate explicit semantics in the form of well-defined media types but introducing higher levels of coupling. We explore Web linking as a lightweight mechanism for representing link semantics and guiding machine-clients in the execution of well-defined choreographies and illustrate our approach with the OAuth and OpenId protocols exploring asynchrony and machine expectations as the interaction moves forward.
Service composition is one of the principles of service-oriented architecture; it enables reuse and allows developers to combine existing services in order to create new services that in turn can be part of another composition. Dynamic composition requires that service components are chosen from a set of services with equal or similar functionality at runtime and possibly automatically. The adoption of the REST services in the industry has led to a growing number of services of this type, many with similar functionality. The existing dynamic composition techniques are method-oriented whereas REST is resource-oriented and consider only traditional (WSDL/SOAP) services. We propose SAW-Q, an extension of simple additive weighting (SAW), as a novel dynamic composition technique that follows the principles of the REST style. Additionally, SAW-Q models quality attributes as a function of the actual service demand instead of the traditional constant values. Our model is much more accurate when compared to real implementation, positively improving the quality of dynamic service compositions.
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