On Querying Data and Metadata in Multiversion Data Warehouse
Wojciech Leja, Robert Wrembel, Robert Ziembicki · IGI Global eBooks · 2010
Methods of designing a data warehouse (DW) usually assume that its structure is static. In practice, however, a DW structure changes among others as the result of the evolution of external data sources, the changes of the real world represented in a DW, and new user requirements. The most advanced research approaches to managing the evolution of DWs are based on temporal extensions and versioning techniques. An important feature of a DW system supporting evolution is its ability to query different DW states. Such querying is challenging since different DW states may differ with respect to their schemas. As a consequence, a system may not be able to execute a query for some DW states. Our approach to managing the evolution of DWs is based on the so-called Multiversion Data Warehouse (MVDW) that is composed of the sequence of DW versions. In this chapter, we contribute a query language called MVDWQL for querying the MVDW. The MVDWQL supports two types of queries, namely content queries and metadata queries. A content query is used for analyzing the content (i.e., data) of multiple DW versions. A metadata query is used for analyzing the history of evolution of the MVDW. The results of both types of queries are graphically visualized in a user interface.