As XML is becoming a de facto standard data exchange format for web-based business applications, it is imperatively required to integrate semantically heterogeneous XML data sources. In this paper, we study a semantic integration of heterogeneous XML data sources. First, we consider a common data model that is designed to capture semantics of XML data. Second, we define semantic conflicts in the context of XML data, and resolve them using the rule-based method. Third, we develop a semantic integration technique of XML data using XML view mechanism. We describe how our approach has been used to integrate heterogeneous XML data sources providing various object-oriented abstraction facilities such as generalization, specialization and aggregation.