Database Reference
In-Depth Information
Relational Algebra
One of the reasons for the success and longevity of the relational model is that it is firmly
grounded on mathematical principles (of linear algebra and set theory), which are well
known and well documented. The (normalized) relational tables are by design, organized
in such a way as to promote and facilitate manipulation of data to yield meaningful
information. As mentioned earlier in the course (chapter 2), data manipulation relates to
the addition, update, deletion, retrieval, reorganization, and aggregation of data. It turns
out that the first three aspects are far more straightforward than the latter three.
In this and the next chapter, the focus is on the latter three aspects of data
manipulation — retrieval, reorganization and aggregation. The intent is to expose you to
the underlying database theory that had to be developed in order to have DBMS suites
that support these data manipulation requirements. As you will soon come to appreciate,
mastery of SQL (which is mandatory, if you intend to do well in this field) or any database
language is greatly enhanced by an understanding of the fundamental underlying theory.
The ecture proceeds under the following sub-topics:
Introduction
Basic Operations of Relational Algebra
Syntax of Relational Algebra
Aliases, Renaming and the Relational Assignment
Other Operations
Summary and Concluding Remarks
7.1 Introduction
Relational algebra consists of a collection of operations on relations. Each operation
produces new relation(s) from one or more already existing relation(s).
Through relational algebra, we can achieve the following objectives:
Defining a scope for retrieval
Defining a scope for update
Defining virtual information
 
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