Abstract. With the ever increasing connection between XML information systems over the Web, users are able to obtain integrated sources of XML information in a cooperative manner, such as developing an XML mediator schema or using eXtensible Stylesheet Language Transformation (XSLT). However, it is not trivial to evaluate the quality of such merged XML data, even when we have the knowledge of the involved XML data sources. Herein, we present a unifying framework for merging XML data and study the quality issues of merged XML information. We capture the coverage of the object sources as well as the structural diversity of XML data objects, respectively, by the two metrics of Information Completeness (IC) and Data Complexity (DC) of the merged data.