This paper presents a formal notation for modelling asynchronous web services composition, using context and coordination mechanisms. Our notation specifies the messages that can be handled by different web services, and describes a system of inter-related web services as the flow of documents between them. The notation allows the typical web services composition pattern, asynchronous messaging, and has the capability to deal with long-running service-to-service interactions and dynamic configuration behaviors. 1 Motivation A service-oriented application is a composition of web services aimed to achieve certain business goals [1,2]. The goals are fulfilled by service-to-service interactions. Our work intends to capture the behavior of service level interactions in a formal notation for specifying web services composition. The language is general and can be applied to various business environments, in order to support web services composition, automation and validation. First of all, a ...