Research On Answer Set Programming And Its Application

M. Gelfond and V. Lifschitz collaboratively established an important kind of model semantics-Stable model semantics for nonmonotonic logic programming in 1988, and expanded this model semantics and renamed it as Answer Set semantics in 1991. Based on this semantics, an important kind of nonmonotonic logic programming technology-Answer Set programming technology was developed. Constrasted with other semantics theories of nonmonotonic logic programming, Answer Set semantics, the kernel of Answer Set programming technology, is concise and simple, and fully utilizes the fruits acquired by the logic programming community, and effectively realizes nonmonotonic reasoning of the logic program. Nowadays, Answer Set programming is not only widely accepted as an important tool of knowledge representation but also a research focus of the logic programming and the nonmonotonic reasoning communities.Based on the investigation of Answer Set programming theory, the innovative contributions included in the thesis are summarized as follows:1. A new method which utilizes weight constraint programming based on Answer Set semantics to automatically resolve the policy conflict is proposed. As policy being widely applied, more and more attention is paid to the policy conflict resolution. Among currently existing approaches, the conflict resolution methods based on logic programming have merits of logical preciseness, high automatization, etc. Whereas, the methods mentioned above have shortcomings, such as limited kinds of resolved conflicts and monotonic optimization mechanism. To overcome these shortcomings above, based on accomplishments of the formal definition of syntax and semantics of policy, the definition of conflict capture mechanism, the conflict classification and the analysis of conflict resolution characters, this thesis fully utilizes the compact representation capability of set selection and flexible optimization sentences of weight constraint programming, to accomplish the creation of weight constraint programs which are used to resolve conflict, etc. This method not only expands the kinds of resolved conflicts but also supplies flexible and multiple optimization mechanisms, thus it effectively overcomes the shortcomings of the previous methods.2. A new Web services composition method based on events is proposed. As the prevalence of electronic business, more and more attention is paid to the Web services automatic composition research. Nowadays, there are two main approaches about Web services composition. One is based on AI (Artificial Intelligence) planning and the other is based on the technologies, such as UML (Unified Modeling Language). Whereas, the former is hardly realized for the difficulty of representation of services composition domain, and the influence of incomplete information. The latter can not satisfy the multiple requirements of users for the insufficient description capability. To obtain an effective approach that is able to satisfy the multiple requirements of the users and can be easily realized, based on accomplishments of a service language based on events, the mechanism to create the composite schema which is used to describe composite services and the analysis of the exclusive services' properties, this thesis utilizes Answer Set programming to represent the composite schema to obtain the composite trajectory which realizes the object of composite services. This method fully utilizes the dynamically executing capability of the policy and the expressive representation capability of Answer Set programming, thus it should have a good application prospect and can satisfy multiple requirements of the users.3. The logic representation of ER Model (Entity-Relationship Model) is accomplished by Answer Set programming. ER Model is a well-known semantic data model and yet widely applied to the database design. Currently there are two main approaches about the improvements for ER model. One is based on the graphical representation and the other is based on the description logic representation. Whereas, the former has not automatic reasoning capability, the latter has shortcomings, such as the weak representation capability and insufficient compatibility with database. To overcome these shortcomings, based on accomplishments of research on the ER model classification, the formal definition of syntax and semantics of ER schema, this thesis utilizes Answer Set programming to represent ER Schema. This method not only supplies a new logic representation approach for ER model, but also effectively overcomes the shortcomings of the approach based on the description logic representation. More importantly, this works above supply the theoretic base for applying ER schema to realize the semantic interoperability among heterogeneous databases.