Web Services are emerging technologies that enable application to application communication and reuse of autonomous services over Web. Composition of web services is a concept of integrating individual web services to conduct complex business transactions based on functionality and performance constraints. To simplify composite web service development, technologies of quality of service (QoS) based web services composition (QWSC) are widely used to build complex applications by discovering the best-fit web services. In this paper, a web service composition system is proposed based on our previous study, a Relaxable QoS-based service selection algorithm (RQSS), to demonstrate its feasibility and performance as well as to share the experiences of developing a web service composition system. The proposed system is compatible with WS-BPEL standards, which can be used for composite web application development through intuitive graphic user interfaces. The experimental results show that the proposed relaxable web composition system performs well with notably improvement for application availability and reliability.