Database Reference
In-Depth Information
Chapter 12
On Querying Data and
Metadata in Multiversion
Data Warehouse *
Wojciech Leja
Poznań University of Technology, Poland
Robert Wrembel
Poznań University of Technology, Poland
Robert Ziembicki
Poznań University of Technology, Poland
ABSTRACT
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 re-
search 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 que-
ries 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.
INTRODUCTION
gained from the advanced analysis of various types
of data processed and collected during the lifetime
of an enterprise. In practice, within the same en-
terprise data are stored in multiple heterogeneous
Contemporary manner of managing enterprises
is based on knowledge. Typically, knowledge is
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