Summary form only given. As extensible markup language (XML) is emerging as the data format of the Internet era. This is creating a new set of data management requirements involving XML, such as the need to store and query XML documents. One way to satisfy these requirements is using relational database by transforming XML data into relations. In this paper we propose a mapping technique that describes how the various definitions in a given XML DTD, such as elements, attributes, parent-child relationships, ID-IDREF(s) attributes can be mapped to entities and relationships, describes how to handle the Union types that are not present in relational model, and shows that XML's ordered data model can be efficiently supported by the unordered relational data model.