We analyze the semantics of composition and QoS among services, and study the discovery and selection processes of composite services, and show a recommend principle of services. In the description of composite service, we present the composite semantics with sequence, selection and concurrent etc. Two services are similar on semantics only if they match well. In the process of service selection, we select the service based on the performance-price ratio, and recommend the service to users with high performance-price ratio principle, which can satisfy the users' needs. The principle is useful to the users in the market environment.
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