Motivated by the need for more flexible OLAP systems, this paper presents work on logical integration of external data in OLAP databases, carried out in cooperation between the Danish OLAP client vendor TARGIT and Aalborg University. Flexibility is ensured by supporting XML as the external data format, since almost all data sources can be efficiently wrapped in XML. Earlier work has resulted in an extension of the TARGIT system, allowing external XML data to be used as dimensions and measures in OLAP databases. This work has led to a number of new ideas for improving the system’s ability to adapt to changes in its surroundings. This paper describes the potential problems that may interrupt the operation of the integration system, in particular those caused by the often autonomous and unreliable nature of external XML data sources, and methods for handling these problems. Specifically, we describe techniques for handling changes in external XML data sources. We also describe techn...