As Web services are increasingly accepted and used, the next step for them is the development of hierarchical and distributed
services that can perform more complex tasks. In this paper, we focus on how to develop guarantees for the performance of
an aggregate service based on the guarantees provided by the lower-level services. In particular, we demonstrate the problem
with an example of an e-commerce Web site implemented using Web services. The example is based on the Trans action Processing
Performance Council (TPC) TPC-W Benchmark [8], which specifies an online store complete with a description of all the func- tionality of the site as well as a description
of how customers use the site. We develop models of the site’s performance based on the performance of two sub-services. The
model’s results are compared to experimental data and are used to predict the performance of the system under varying conditions.
This material is based upon work supported in part by the National Science Foun- dation under Grant No. 9975019 and IBM. Any
opinions, findings, and conclusions or recommendations expressed in this material are those of the author (s) and do not necessarily
reflect the views of the National Science Foundation or IBM. This work was done in part while Mr. Daly was an intern at IBM
T.J. Watson Research Center.