在服务规则库的基础上,介绍了回溯树与完备回溯树的概念,并证明了其重要性质.提出了基于回溯树的Web服务自动组合方法.该方法采用分步分治的思想进行服务的自动组合:1)针对用户请求的输出对象生成完备回溯树;2)在完备回溯树中选取最佳生成源(生成路径);3)将生成路径合成为可执行的流程服务.与已有的基于图搜索的自动Web服务组合方法相比,该方法极大地减小了搜索空间,避免了循环搜索,能够满足单目标和多目标的用户请求.仿真实验结果表明,该方法能够在大规模的服务规则库中进行快速的服务组合,从而满足用户请求.
An approach based on backward tree to compose services automatically is proposed. It composes services for a user through three steps: 1) Builds a complete backward trees on-line; 2) Searches for optimal valid generation sources (generation-paths); 3) Composes generation paths. Compared to traditional graph-based methods it has a smaller search space and avoids the repetition search. Experimental results show that this method has a good performance even the repository has a large number of services.