This paper introduces a cooperative service composition language called CCML which aims to facilitate the description of services, their interfaces and their behavior, further to reduce the complexity required to compose services. Interaction rules among services rely on a cooperative computation model, i.e. KPN (Kahn Process Network), which adopts dataflow and channel based asynchronous communication pattern among process nodes. Formal model for behavioral semantics of CCML is based on CCS process algebra which presents a high expressive power, capable of capturing CCML behavioral semantics. We give an operational semantics to CCML in the form of a labeled transition system (LTS) and describe the events of a LTS associated to the main CCML constructs, which are sequence, condition, loop and parallel. Finally, we present an application case to show how to describe service composition using CCML.