Extending Business Process Execution Language for Web Services with Service Level Agreements Expressed in Computational Quality Attributes

Quality of Service (QoS) management is critical for service-oriented enterprise architectures because services have different QoS characteristics, requesters have different requirements, and service interactions are decoupled. This paper proposes a QoS Management Architecture for dynamic processing of service- and flow-level quality attributes to support QoS requests and analyses in Web-service-oriented architectures. The architecture is implemented using Business Process Execution Language for Web Services (BPEL4WS), an interoperable integration model that facilitates automated process integration). The proposed approach extends BPEL4WS by integrating it with Web service-level agreements (WSLA) to support QoS and extending the BPEL4WS language to provide a new "<agreement>" assertion that describes the location of a document\´s WSLA document. Under the proposed approach, quality attributes are defined, computed, and acted upon as dynamic characteristics of systems, with values constantly changing in operation The feasibility of the proposed approach is demonstrated using an illustrative travel reservation service flow example.