Federated database systems for managing distributed, heterogeneous, and autonomous databases
ACM Computing Surveys (CSUR) - Special issue on heterogeneous databases
Microsoft OLAP solutions
Eddies: continuously adaptive query processing
SIGMOD '00 Proceedings of the 2000 ACM SIGMOD international conference on Management of data
Monitoring XML data on the Web
SIGMOD '01 Proceedings of the 2001 ACM SIGMOD international conference on Management of data
Graph Structured Views and Their Incremental Maintenance
ICDE '98 Proceedings of the Fourteenth International Conference on Data Engineering
Change-Centric Management of Versions in an XML Warehouse
Proceedings of the 27th International Conference on Very Large Data Bases
Xyleme: A Dynamic Warehouse for XML Data of the Web
IDEAS '01 Proceedings of the International Database Engineering & Applications Symposium
SSDBM '02 Proceedings of the 14th International Conference on Scientific and Statistical Database Management
Detecting Data and Schema Changes in Scientific Documents
ADL '00 Proceedings of the IEEE Advances in Digital Libraries 2000
Detecting Changes in XML Documents
ICDE '02 Proceedings of the 18th International Conference on Data Engineering
Views as first-class citizens in object-oriented databases
The VLDB Journal — The International Journal on Very Large Data Bases
Finding an application-appropriate model for XML data warehouses
Information Systems
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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 idea 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 techniques for improving the reliability of external XML sources, e.g., when these are found on the Internet, by dynamically trying to locate alternative sources during the evaluation of a query. Finally, we discuss solutions to a number of other possible problems, and show how the techniques can be integrated in the targit architecture. Experiments performed with a prototype implementation of central functionality shows the viability of the proposed solutions.