Web services are emerging technologies which satisfy users' requests on the web. Selecting appropriate services to suit the needs is a huge task. There are a huge number of service providers who offer same type of service, with differences in functional and non functional qualities. A few users may need multiple services at the same moment. So composition of services also becomes important. Moreover the consumers get confused in selecting apt services, which leads to the necessity of an automated service selection mechanism based on QoS metrics.