The
basic concepts of the model include facts, measures, dimensions, and hierarchies.
The DFM suits the variety of modeling situations that may be encountered in real
projects of small to large complexity. The chapter provides a comprehensive set of
xv
solutions for conceptual modeling according to the DFM and serves a DW designer
as a practical guide for applying different modeling solutions. The chapter provides
also a foundation for the rest of the book as it discusses fundamental concepts used
in the DW technology, among others: multidimensional modeling; dimensions and
their attributes; and shared, incomplete, recursive, and dynamic hierarchies.
Chapter II, Handling Structural Heterogeneity in OLAP, by Carlos A. Hurtado
and Claudio Gutierrez, goes beyond the DFM model and it focuses on modeling
dimensions that may have different structures; that is, they are heterogeneous. Such
dimensions are created as the result of mixing multiple dimensions with different
structures into a single dimension. In the chapter, the authors show how to incorporate
structural heterogeneity in the design of OLAP models, explain why structural
heterogeneity weakens aggregate navigation, survey different techniques to deal with
heterogeneity, present a class of dimension integrity constraints to model structural
heterogeneity, and demonstrate the practical application of dimension constraints
to support aggregate navigation.
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