Web services are a key technology for automating inter-organizational interactions. Enterprises can externalise parts of their business processes using them. Then they can dynamically combine existing services to offer value added composite services (CS). One remaining problem is how to ensure a correct composition and a reliable execution of a CS with regards to partners transactional requirements. In this paper, we present a transactional approach to ensure the failure atomicity of CS required by partners. Partners specify their CS and the requested failure atomicity. Then, we use a set of rules to validate the composite service with regards to designers transactional requirements.