The Application Service Provider (ASP) has started to use Web services to expose data sources and adopted Service Oriented Architecture (SOA) to build data integration infrastructure. XML data integration and mediation in SOA is a complex task. The existing mediation technologies and commercial tools take XSLT as the standard to transform and merge XML documents from various Web services with the intension to deliver a unified view of data. As the number of involved data Web services increases, the XSLT transformation programs lead to poor modifiability and are difficult to reuse. After a systematic evaluation on the existing XML query and transformation languages based on the defined selection criteria, we propose a services oriented architecture in which a declarative rule-based technique is introduced for XML data transformation. At design time, we reuse and adapt Xcerpt as our integration language that represents integration rules in a declarative and reusable manner. At runtime, the mediated software architecture provides the support of automatically generating the definition and the construction of the service connectors that mediate data from various Web services involved in integration flows. We found through working examples that the software architecture improves the modifiability of the data integration architecture.