Conceptual Data Warehouse Design - Data Warehouse Systems: Design and Implementation - page 113

4.7 Review Questions
4.1 Discuss the following concepts: dimension, level, attribute, identifier,
fact, role, measure, hierarchy, parent-child relationship, cardinalities,
root level, and leaf level.
4.2 Explain the difference, at the schema and at the instance level, between
balanced and unbalanced hierarchies.
4.3 Give an example of a recursive hierarchy. Explain how to represent an
unbalanced hierarchy with a recursive one.
4.4 Explain the usefulness of generalized hierarchies. To which concept of
the entity-relationship model are these hierarchies related?
4.5 What is a splitting level? What is a joining level? Does a generalized
hierarchy always have a joining level?
4.6 Explain why ragged hierarchies are a particular case of generalized
hierarchies.
4.7 Explain in what situations alternative hierarchies are used.
4.8 Describe the difference between parallel dependent and parallel inde-
pendent hierarchies.
4.9 Illustrate with examples the difference between generalized, alternative,
and parallel hierarchies.
4.10 What is the difference between strict and nonstrict hierarchies?
4.11 Illustrate with an example the problem of double counting of measures
for nonstrict hierarchies. Describe different solutions to this problem.
4.12 What is a distributing attribute? Explain the importance of choosing
an appropriate distributing attribute.
4.13 What does it mean to have a fact with multiple granularities?
4.14 Relate the problem of double counting to the functional and multival-
ued dependencies that hold in a fact.
4.15 Why must a fact be decomposed in the presence of dependencies? Show
an example of a fact that can be decomposed differently according to
the dependencies that hold on it.
4.8 Exercises
4.1 Design a MultiDim schema for an application domain that you are
familiar with. Make sure that the schema has a fact with associated
levels and measures, at least two hierarchies, one of them with an exclu-
sive relationship, and a parent-child relationship with a distributing
attribute.
4.2 Design a MultiDim schema for the telephone provider application in
Ex. 3.1 .
4.3 Design a MultiDim schema for the train application in Ex. 3.2 .