Now-a-days web services and SOA (Service Oriented Architecture) systems have fundamental significance in computer science, especially in platform integration. The most common consideration is system workload estimation. Interacting composite web services can be modeled as asynchronously interacting BPEL processes. In order to compute key system workload parameters in design time – such as service time of a process, response time or resource cost – the standard BPEL model was extended with new terms and attributes.