Database Reference
In-Depth Information
Relational Calculus
This chapter discusses relational calculus as an alternate way of manipulating relations in
a database. The partial college database, introduced in the previous chapter (Figures 7-1
and 7-2) will be used as a frame or reference. It must be constantly borne in mind that
relational algebra and relational calculus are mutual equivalents; most DBMS suites will
implement one or the other, or aspects of both, depending on what is convenient to the
developers. The chapter proceeds under the following subtopics:
•
Introduction
•
Calculus Notations and Illustrations
•
Quantifiers, Free and Bound Variables
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Substitution Rule and Standardization Rules
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Query Optimization
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Domain Related Calculus
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Summary and Concluding Remarks
8.1 Introduction
In relational calculus, we simply specify what is required, not how to obtain the required
relation(s). Relational algebra, on the other hand, provides a collection of explicit
operations in SELECT, JOIN, PROJECT etc., which can be used to tell the system how to
derive desired relation(s).
Example 1:
Suppose that we are interested in obtaining a list of program names and
associated course names for the Bachelor of Science in MIS.