关键词: Datalog语言，逻辑程序，程序调用，数字版权保护

Abstract: The paper firstly gave the call semantic and call predicates of datalog logic programs, and discussed the operational and fixpoint semantics of U-datalog programs with call predicates. Then the algorithms that evaluate U-Datalog programs with call predicates under definite stratified calls were presented. Finally, applications of the call semantic of datalog programs in digital rights management were explained and demonstrated.

Key words: Datalog language, Logic program, Program call, Digital rights management(DRM)