Abstract. There are two types of behavioural model in the WSMO semantic description of services: an orchestration and a choreography, together called the interface. While an orchestration defines a service's behaviour as a composition of existing parts, a choreography is intended to document the conversation of messages exchanged with a single client. In this paper we present a three-level model for behavioural descriptions, and how the Cashew workflow model fits into this, building on existing work in, and establishing connections with, semantic web services, workflow, and software engineering design.