Formal mapping of WSLA contracts on stochastic models

Abstract

Service level agreement (SLA) specification languages are designed to express monitorable contracts between service providers and consumers. It is of interest to determine if predictive models can be derived for SLAs expressed in such languages, if possible in automated fashion. For this purpose, we study in this paper the mapping of the Web Service Level Agreement (WSLA) into reward metrics defined in the Stochastic Discrete Event Systems (SDES) formalism. We associate a formal semantics with WSLA elements and map these on SDES through a five step mapping process, which includes expressions for the metrics and functions on these metrics, the time at which to predict, and the ultimate service level compliance probability. We illustrate our approach through a stock quote web service example. © 2011 Springer-Verlag.