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Time in Multidimensional Databases

In spite of the obvious importance of time in data warehousing and OLAP, current commercial systems do not support tracking the history of a data warehouse, either at the schema or instance level. In this chapter we address this issue, introducing the Temporal Multidimensional Model and a query language, denoted TOLAP, allowing expressing temporal OLAP queries at a high level of abstraction. Further, we show that previous work in temporal databases needs to be extended in order to handle evolution and versioning in OLAP. Finally, we present an implementation, along with preliminary experimental results.