chapter2 - intro to rdbms

7/28/2019 Chapter2 - Intro to Rdbms

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INTRODUCTION TO RDBMS


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Objectives

After completing this chapter, you will be able to:

Define a Relational Database Management System

(RDBMS)

Define a relation

List the features of an RDBMS

List Important terms related to RDBMS

Describe the different types ofkeys and their use

Explain referential integrity


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Basic Definitions

RELATIONAL DATABASE

A relational database is a database system in which

the database is organized and accessed according

to the relationships between data items without

the need for any consideration of physical

orientation and relationship.

Relationships between data items are expressed by

means oftables.

It is a tool which can help you store, manage and disseminateinformation of various kinds. It is a collection of objects, tables,


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RELATIONAL DATABASE MANAGEMENT SYSTEM

It is a system which allows us to perceive data as tables

(and nothing but tables) and operatorsnecessary to

manipulate that data are at the users disposal.

The operators used are:

SELECT

PROJECT

JOIN

Definitions continued...


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Features of RDBMS

The ability to create multiple relations (tables) and

enter data into them.

An interactive query language.Retrieval of information stored in more than one

table.

Provides aCatalogor Dictionary, which itselfconsists of tables ( called system tables )


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Important Terms

Relation : a tableTuple : a row in a table

Attribute : a column in a table

Degree : number of attributesCardinality : number of tuples

Primary Key : a unique identifier for the

tableDomain : a pool of values from which

specific attributes of specific relations draw

their values


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Properties of a Relation (Table)

There are no duplicate rows (tuples).

Tuples are unordered, top to bottom.

Attributes are unordered, left to right.

All attribute values are atomic (or scalar).

Relational databases do not allow repeating

groups.

A database relation is a predefined row/column

format for storing information in a relational


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Keys

Key

An attribute or set of attributes whose values uniquely

identify each entity in an entity set is called a key for

that entity set.

Super Key

If we add additional attributes to a key, the resulting

combination would still uniquely identify an instance

of the entity set. Such augmented keys are called super


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Referential Integrity

It is an integrity constraint which specifies that the value(or existence) of an attribute in one relation depends on

the value (or existence) of an attribute in the same or

another relation.

Referential integrity in a relational database is consistency

between coupled tables.

It is usually enforced by the combination of a primary key

and a foreign key.For referential integrity to hold, any field in a table that is

declared a foreign key can contain only values from a

parent table's primary key field.


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sid cid grade53666 carnatic101 C

53688 reggae203 B

53650 topology112 A

53666 history105 B

sid name age

53666 Jones 18

53688 Smith 18

53650 Smith 19

gpa

3.4

3.2

3.8

login

Jones@cs

Smith@eecs

Smith@math

Enrolled Student

Primary keyForeign key referring tosid of STUDENT relation

Keys and Referential Integrity


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Summary

You now should be able to:

1.Define a Relational Database Management System

(RDBMS)

2.Define a relation

3.List the features of an RDBMS

4.List Important terms related to RDBMS

5.Describe the different types ofkeys and their use

6.Explain referential integrity

chapter2 - intro to rdbms

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