The last decade has witnessed a tremendous growth of Web services as a major technology for sharing data, computing resources, and programs on the Web. With increasing adoption and presence of Web services, designing novel approaches for efficient and effective Web service recommendation has become of paramount importance. Most existing Web service discovery and recommendation approaches focus on either perishing UDDI registries, or keyword-dominant Web service search engines, which possess many limitations such as poor recommendation performance and heavy dependence on correct and complex queries from users. It would be desirable for a system to recommend Web services that align with users' interests without requiring the users to explicitly specify queries. Recent research efforts on Web service recommendation center on two prominent approaches: collaborative filtering and content-based recommendation. Unfortunately, both approaches have some drawbacks, which restrict their applicability in Web service recommendation. In this paper, we propose a novel approach that unifies collaborative filtering and content-based recommendations. In particular, our approach considers simultaneously both rating data (e.g., QoS) and semantic content data (e.g., functionalities) of Web services using a probabilistic generative model. In our model, unobservable user preferences are represented by introducing a set of latent variables, which can be statistically estimated. To verify the proposed approach, we conduct experiments using 3,693 real-world Web services. The experimental results show that our approach outperforms the state-of-the-art methods on recommendation performance.

Service composition is becoming the dominant paradigm for developing Web service applications. It is important to ensure that a service composition complies with the requirements for the application. A rigorous compliance checking approach usually needs the requirements being specified in property specification formalisms such as temporal logics, which are difficult for ordinary software practitioners to comprehend. In this paper, we propose a property pattern based specification language, named PROPOLS, and use it to verify BPEL service composition schemas. PROPOLS is easy to understand and use, yet is formally based. It builds on Dwyer et al.'s property pattern system and extends it with the logical composition of patterns to accommodate the specification of complex requirements. PROPOLS is encoded in an ontology language, OWL, to facilitate the sharing and reuse of domain knowledge. A Finite State Automata based framework for verifying BPEL schemas against PROPOLS properties is also discussed.

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