Page 173 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Database Management Systems/Managing Database Mithilesh Kumar Dubey, Lovely Professional University

Notes Unit 10: Datalog and Recursion

CONTENTS
Objectives
Introduction

10.1 Datalog and Recursion
10.2 Evaluation of Datalog Program
10.3 Recursive Queries and Negation

10.4 Modeling Complex Data Semantics
10.5 Specialization
10.6 Generalization
10.7 Summary
10.8 Keywords

10.9 Self Assessment
10.10 Review Questions
10.11 Further Readings

Objectives

After studying this unit, you will be able to:
 Know datalog and recursion
 Describe datalog program evaluation
 Explain specialization and generalization

Introduction

While relational algebra can express many useful operations on relations, there are some
computations that cannot be written as an expression of relational algebra. A common kind of
operation on data that we cannot express in relational algebra involves an infinite, recursively
defined sequence of similar expressions.

10.1 Datalog and Recursion

We now define a relation called Components that identifies the components of every part.
Consider the following program, or collection of rules:
Components (Part, Subpart): Assembly (Part, Subpart, Qty).
Components (Part, Subpart): Assembly (Part, Part2, Qty),

Components (Part2, Subpart):

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