Conceptual Data Warehouse Design - Data Warehouse Systems: Design and Implementation - page 86

Chapter 4
Conceptual Data Warehouse Design
The advantages of using conceptual models for designing databases are
well known. Conceptual models facilitate communication between users
and designers since they do not require knowledge about specific features
of the underlying implementation platform. Further, schemas developed
using conceptual models can be mapped to various logical models, such
as relational, object-relational, or object-oriented models, thus simplifying
responses to changes in the technology used. Moreover, conceptual models
facilitate the database maintenance and evolution, since they focus on users'
requirements; as a consequence, they provide better support for subsequent
changes in the logical and physical schemas.
In this chapter, we focus our study on conceptual modeling for data
warehouses. In particular, we base our presentation in the MultiDim model,
which can be used to represent the data requirements of data warehouse and
OLAP applications. The definition of the model is given in Sect. 4.1 .Since
hierarchies are essential for exploiting data warehouse and OLAP systems
to their full capabilities, in Sect. 4.2 , we consider various kinds of hierarchies
that exist in real-world situations. We classify these hierarchies, giving a
graphical representation of them and emphasizing the differences between
them. We also present advanced aspects of conceptual modeling in Sect. 4.3 .
Finally, in Sect. 4.4 ,werevisittheOLAPoperationsthatwepresentedin
Chap. 2 by addressing a set of queries to the Northwind data warehouse.
4.1 Conceptual Modeling of Data Warehouses
As studied in Chap. 2 , the conventional database design process includes the
creation of database schemas at three different levels: conceptual, logical,
and physical. A conceptual schema is a concise description of the users'
data requirements without taking into account implementation details.