A First Approach to Model SLAs for Composite Services, using WS-Agreement

Abstract. When organizations began to use intensively services ori-ented applications (SOA) they arose the need of service level agreements (SLAs) to provide the confidence needed on quality of service (QoS). Nowadays, we have a consensus on what an SLA for a service is and as consequence, languages to specify SLAs as WS-Agreement have been proposed and they are becoming popular. One of the key topics in SOA research at present are composite services (CS). CS have been tackled by many authors and there is a consensus on their definition. However, not many works deal with SLAs for CS. The reason could be the lack of an intensive use of CS applications in business context. But in future CS applications comprised by heterogeneous services-defined in diverse specification languages or supported by different platforms- may gain the attention of companies and they will need a QoS support. Then, we con-sider interesting to obtain a general definition of SLAs for CS starting from current proposals. In this paper we analyze different meanings given in the literature for the expression SLAs for CS, we find the shared as-pects, we study the unshared ones and we propose to include important additional elements into our abstract model for defining SLAs for CS, such as temporal information and QoS properties about the whole CS. Finally, we promote the use of WS-Agreement with some non-intrusive extensions proposed by us for the establishment of SLAs for CS according to our abstract model, including several use cases.