Database Reference
In-Depth Information
Chapter 2
Improving Expressive Power
in Modeling Data Warehouse
and OLAP Applications
Elzbieta Malinowski
University of Costa Rica, Costa Rica
ABStrAct
Data warehouse and OLAP systems are widely required during the decision-support process, since they
provide integrated data in a form that facilitates the expression of complex queries. In order to exploit both
systems to their full capabilities, dimensions with hierarchies must be clearly defined. Dimensions can
be of different types and they allow users to see quantified data from different perspectives. Hierarchies
are important in analytical applications, since they give users the possibility of representing data at
different abstraction levels. However, even though there are different kinds of hierarchies in real-world
applications and some of them are already implemented in commercial tools, there is still a lack of a
well-accepted conceptual model that allows decision-making users to express their analysis needs. In this
chapter, we show how the conceptual multidimensional model can be used to facilitate the representation
of complex hierarchies and different kinds of dimensions in comparison to their representation in the
relational model and commercial OLAP tools, using as an example Microsoft Analysis Services.
IntroductIon
to access and analyze the data contained in DWs.
These systems allow users to interactively query
and automatically aggregate data using roll-up
and drill-down operations. The former operation
transforms detailed data into a summarized one,
e.g., daily sales into monthly sales, while the latter
operation does the contrary.
The data for DW and OLAP systems is usu-
ally organized into fact tables related to several
dimension tables. A fact table ( Sales in Figure
A Data Warehouse (DW) provides users with high
quality data organized in a way that facilitates
expression of complex queries, ensuring at the
same time efficient and accurate responses to such
queries. Different systems and tools, such as online
analytical processing ( OLAP) systems, can be used
Search WWH ::




Custom Search