Database Reference
In-Depth Information
5.11 Summary
In this chapter, we have studied the problem of logical design of data
warehouses, specifically relational data warehouse design. Several alternatives
were discussed: the star, snowflake, starflake, and constellation schemas. Like
in the case of operational databases, we provided rules for translating concep-
tual multidimensional schemas to logical schemas. Particular importance was
given to the representation of the various kinds of hierarchies that can occur
in practice. The problem of slowly changing dimensions was also addressed in
detail. We then explained how the OLAP operations can be implemented on
the relational model using the SQL language and also reviewed the advanced
features SQL provides through the SQL/OLAP extension. We concluded
the chapter showing how we can implement the Northwind data cube over
Microsoft Analysis Services and Mondrian, starting from the Northwind data
warehouse.
5.12 Bibliographic Notes
A comprehensive reference to data warehouse modeling can be found in the
topic by Kimball and Ross [
103
]. A work by Jagadish et al. [
95
] discusses
the uses of hierarchies in data warehousing. Complex hierarchies like the
ones discussed in this chapter were studied, among other works, in [
84
,
87
,
159
,
160
]. The problem of summarizability is studied in the classic paper of
Lenz and Shoshani [
115
] and in [
85
,
86
]. Following the ideas of Codd for
the relational model, there have been attempts to define normal forms for
multidimensional databases [
114
]. Regarding SQL, analytics and OLAP are
covered in the topics [
27
,
132
]. There is a wide array of topics on Analysis
Services that describe in detail the functionalities and capabilities of this
tool [
71
,
79
,
163
,
182
,
183
]. Finally, a description of Mondrian can be found in
the topics [
10
,
18
].
5.13 Review Questions
5.1
Describe the differences between the following concepts:
(a) Relational OLAP (ROLAP), multidimensional OLAP (MOLAP),
and hybrid OLAP (HOLAP).
(b) Star schema, snowflake schema, starflake schema, and constellation
schema.
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