Based on the framework of service-oriented architecture (SOA), complex distributed systems can be dynamically and automatically composed by integrating distributed Web services provided by different organizations, making dependability of the distributed SOA systems a big challenge. In this paper, we propose a QoS-aware fault tolerant middleware to attack this critical problem. Our middleware includes a user-collaborated QoS model, various fault tolerance strategies, and a context-aware

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... in determining optimal fault tolerance strategy for both stateless and stateful Web services. The benefits of the proposed middleware are demonstrated by experiments, and the performance of the optimal fault tolerance strategy selection algorithm is investigated extensively. As illustrated by the experimental results, fault tolerance for the distributed SOA systems can be efficient, effective and optimized by the proposed middleware. 978-1-4244-4421-2/09/$25.00 c 2009 IEEE 978-1-4244-4421-2/09/$25.00 c 2009 IEEE