| The exist OLAP system can not deal with real-time dynamic data although it is very important. It lacks enough efficiency when handles rapid change of unexpected data requirement. Physical integrating is a complex and timeconsuming process and need the multidimensionaset to be rebuilt. Logical integrating is a better way. It can provide enough efficiency and satisfy the demand of speed and function. In this paper, the external data is logically integrated with OLAP multidimensional set by using the widely-used XML format to realize the federal data query.Firstly, this paper discusses the importance of integrating external realtime dynamic data and the virtue of logical integratin than physical integrateing. After that, it introduces the multidimensional data model and the selection algorithm, grouping algorithm based on it. At the same time it introduces the XML data model and XPath query language which are used in the federal system.Secondly, this paper discusses the method of building federal data model from multidimensional data model and XML data model by links and level expressions. This makes it possible to reference external XML data in OLAP query and enables the use of XML data for decoration, selection and grouping by using the decoration algorithm, extended selection algorithm and extended aggregation algorithm on federal data model. And it also realizes the federal data query algorithm on the federal data model by those algorithms.At last, this paper discusses the partition query tree algorithm on the bases of 16 algebraic transformation rules. It partitions the query tree in order to reduce the amount of federal query data and improve the efficiency of federal data query.
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