应用合适的形式系统对语义Web服务建模是实现语义Web服务自动组合的前提;形式系统的表达能力和计算性能决定了语义Web服务组合的准确度和求解效率.动态描述逻辑DDL(X)将动态逻辑、描述逻辑以及构建在描述逻辑之上的动作理论有机地结合,为语义Web服务的建模提供了新的工具.提出了一种基于DDL(X)的语义Web服务自动组合方法.首先,在将OWL-S表示的语义Web服务建模为动作的基础上,将语义Web服务组合问题建模为基于DDL(X)的规划问题,其中规划问题的规划解可以由DDL(X)中的任一动作构成,从而可以支持OWL-S中不含有Split和Split+Join的各种Web服务组合方案.针对建模后得到的任一规划问题,给出了用来判断是否存在规划解的判定算法,证明了算法的可终止性、可靠性和完备性.最后,当规划解存在时,可以根据判定过程将其解析出来.文中的方法充分发挥了DDL(X)在表达能力和计算性能等方面的优势,为语义Web服务自动组合提供了一套有效的理论工具.
In order to realize automatic composition of semantic Web services, a basic step is to model these services with suitable formal systems; both the accuracy and the efficiency of the composition are determined by the expressive power and the computing property of the formal system adopted. The dynamic description logic DDL(X) is a combination of dynamic logics, description logics and action formalisms constructed over description logics~ it provides a new tool for modeling and reasoning about semantic Web services. Based on DDL(X), this paper intro- duces a method for automatic composition of semantic Web services. Firstly, by translating semantic Web services described by OWL-S into actions, the composition problem is modeled as a planning problem based on DDL(X). Since each solution of the planning problem is formed by actions of DDL(X), any compositions specified by OWL-S, except those with the Split and Split- Join control structures, can be taken into account. Secondly, for any planning problem constructed above, an algorithm for deciding the existence of solutions is developed. The termination,soundness and completeness of this algorithm are proved. Finally, in the case that there exist solutions for the planning problem, it is demonstrated that one of the solutions can be generated from the deciding procedure. This method takes advantages of both the expressive power and the computing property of DDL(X). It provides a suit of effective theoretical tools for automatic composition of semantic Web services.