Data model is a key research field in the community of XML data management. However, the existed works fall short in their ability to model complex data structure of XML database or to support complete operations. This paper proposes a new mapping-based data model. This model aims to give the precisely defined notations for complex data structure and semantics of XML database. Along with the model, this paper also presents an associated algebra formally which includes a set of path expression operations and data modification operations. This model has already adopted in an XML-based information integration system. It shows that this model can give the precise semantics of XML database, and support the XML database applications effectively.