RDBMS.ppt What is RDBMS RDBMS stands for Relational Database Management System.

Copyright © 2009, Oracle. All rights reserved.
Introduction

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Requirements of an Application:

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 Information is a critical factor for any business to be successful.
Information is extracted from data stored in databases.
 Database is an integral part of an organization. Aspiring database
developers should be able to efficiently design and implement
databases.
 Knowledge of these will enable the developers to build robust
database solutions.
 This module will help students to understand the concepts related
to relational databases.

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What is a
Database?

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 A database is a collection of logically related data.
 Data means known facts, which are meaningful and can be
recorded.
For example:
Hard Disk
Address
Book

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 Database Management is the task of maintaining databases so that
the information is easily available.
 Database Management Systems (DBMS) is the software required
to perform the task of maintaining databases.
 Management of data involves:
 Defining structures for data storage.
 Providing methods for data manipulation, such as adding, editing,
and deleting data.
 Providing data security against unauthorized access.
 Database management systems are now available on a wide range
of computers, from desktops to mainframes. The size and power of
the computer determines the system facilities, such as security and
storage.

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The main objectives of any DBMS are to:
 Provide an efficient and easy way to store, update, and retrieve data
from a database.
 Manage information about users who interact with the DBMS, and the
tasks that these users can perform on the data.
Today, relational databases are the most popular form of storing
data. Besides storing data and extracting information, a database has
to be managed effectively. The software that is used to manage and
retrieve information in a relational database is called a Relational
Database Management System (RDBMS).
A Relational Database Management System (RDBMS) is an
advanced version of DBMS that also defines the relationship between
various data values.

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 Some typical applications of an RDBMS are:
 Airline and railway reservations
 Banking applications
 Manufacturing industry
 Order processing
 Hospital management systems
 Library management systems
 Hotel industry

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Several RDBMS products are available today. Some popular products are:
 Oracle
 Microsoft SQL Server
 Sybase
 Ingres
 DB2

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Now, let us understand the
working of DBMS.

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Database
DBMS
Request for
data
Retrieved data
returned as a result
User system to extract
information from the
database

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 Relational data structure:
 Each table in a database has a unique table name.
 The row (or record) in the table is called a tuple.
 The column (or field) is called an attribute.
 Every column in a table must have a unique name.
 The number of tuples is called the cardinality of the table.
 The number of attributes is called the degree of the table.
 Rows are unordered in a relation.
 A column or combination of columns that uniquely identifies each row in
the table is called the primary key of the table.
 A table where every row is different from all other rows is called a relation.
 A domain is a collection of values from which one or more attributes
(columns) draw their actual values.

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The following diagram describes the data structure of an RDBMS.
T_CODE NAME AGE SEMESTER
I1001 Nancy Mathews 27 I
I1002 Catherine 38 II
I1003 Mac Thams 50 IV
I1004 Joe Nelson 35 III
Tuple

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Attributes

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Primary Key
Relation

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DOMAIN
T_CODE
DOMAIN
NAME
DOMAIN
AGE
DOMAIN
SEMESTER

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 Representing missing information:
 In RDBMS, missing or unknown information is represented as a NULL
value in a table.
 NULL is not the same as space or zero.
 Representing relationships in an RDBMS:
 A column in one table whose value matches the primary key in some
other table is called a foreign key.
 A primary key and a foreign key create a parent-child relationship
between the tables that connect them.

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 The ER (Entity-Relationship) model:
Views the real world as a collection of objects or entities and the relationship
among them.
It also has a corresponding diagramming technique.
STUDENT COURSE
LEARN
Sno Sname CrsID Crsname
Entities
Relationship
Attributes Attributes

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 An entity:
 Is any object, place, person, or activity about which the data is recorded.
 Can be categorized as entity type and entity instance.
 In the ER model diagramming technique, entities are named and represented
inside a box.
For example:
TEACHER

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 Entity can be of the following types:
Dependent entity:
Depends on another entity for existence.
Is also called as a weak entity.
Independent entity:
Does not depend on any other entity for existence.
Is also called as a regular entity.
Independent
Entity
Dependent
Entity

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 Relationship among entities:
 A relationship is depicted as a diamond with the name of the
relationship type.
Relationship
For example:

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 The following diagram represents the association of an entity with itself.
STUDENT
SEMINAR
An entity associating with
itself can be a student giving
a seminar presentation to
other students.

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 The following statement has been extracted from a case presented by a
manufacturer regarding the maintenance of their data: “A supplier ships
certain parts”. Identify the entities mentioned in this statement, and their
relationship. Draw a diagram depicting the relationship.
Solution:
Entities: SUPPLIER, PARTS
Relationship: SHIP or SUPPLIES

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 There are three types of relationships:
One-to-one
One-to-many (or Many-to-one)
Many-to-many

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 The following diagram represents the one-to-one relationship between
DEPARTMENT and DEPARTMENT HEAD.
For a particular DEPARTMENT there can be only one DEPARTMENT HEAD.

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 The following diagram represents the many-to-one relationship between
STUDENT and MAJOR.
A STUDENT can MAJOR in only one course, but many STUDENTs can register for a
given MAJOR course.

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 The following diagram represents the many-to-many relationship between
STUDENT and COURSE.
A STUDENT can take many COURSEs and many STUDENTs can register for a given COURSE.

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 What do the following ER diagrams represent?
Solution:
Many students can work on many projects.
Many employees belong to only one department.

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 Consider the following statement of a manufacturing company:
“A supplier supplies certain parts. A particular part is not necessarily supplied
by only one supplier. No supplier supplies only a single part.” What type of
relationship is this? Draw a diagram to depict the relationship.
Solution:
Many-to-many relationship

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 An attribute:
Is a property of a given entity.
Is depicted as ellipses, labeled with the name of the property.
The following diagram shows the various attributes of the entity, STUDENT.

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 A manufacturer needs to maintain the following details about the supplier:
Name
Address
Credit status
Assigned code number
Draw a diagram to depict this information.
Solution:

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 A subtype:
Is a subset of another entity.
Is always dependent on the supertype for its existence.
 The attributes of a supertype apply to all of its subtypes.

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 The following diagram shows the relationship between supertype
(PATIENT) and subtypes (INPATIENT and OUTPATIENT).
PATIENT
ID
Name
Addr
OUTPATIENT
INPATIENT
VstDate
RoomNo BedNo

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Map an ER diagram to a table
 The following components play an important part while mapping an
ER diagram to table:
o Regular entities
o Attributes
o Relationships
o Weak entities
o Subtypes and supertypes

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 Regular entities:
 They can exist alone, independent of any other entity.
 They are the “building blocks” of the database.
 Each regular entity maps to a table.
 For example, STUDENT and BOOKS are two separate entities in the
following ER diagram.
STUDENT BOOKS
ISSUES

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 Attributes:
 Each property or attribute shown in the ER diagram maps to an attribute
in the appropriate table.
 In the following ER diagram, STUDENT and BOOKS individually has
different attributes.
Entity becomes the table and the
attributes of the entity become
columns of the table.

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 Relationships:
There are the following types of relationships:
 One-to-One
 One-to-Many
 Many-to-Many

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 One-to-one relationship:
 One instance of an entity can relate to only one instance of the related entity.
If frequent queries require data from
the two tables, then it is better to
merge the two tables to improve
query performance.
For example:

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 One-to-many relationship:
 One instance of an entity can relate to more than one instance of the related entity.
Mapped to the
DEPARTMENT
table
Mapped to the
EMPLOYEE
table
For example:

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 Many-to-many relationship:
 Many instances of an entity can relate to more than one instance of the related
entity.
The primary keys, ROLL_NO and CODE of
the STUDENT and BOOKS table will act as
the foreign keys in the ISSUE table.
Mapped to the
STUDENT
table
Mapped to
the BOOKS
table
Mapped to
the ISSUES
table
For example:

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 For example, a user wants to know which book was issued to a particular
student and on which date. You can use the foreign keys in the ISSUE table to
make a join between all the three tables.
ROLL_NO NAME CODE DESC ISSUE_DATE RETURN_DATE
 What is the primary key of the ISSUE table? There are two possibilities. One
possibility is to take a combination of the two foreign keys (ROLL_NO and CODE)
The resulting key is known as Composite Key.
 Another possibility is to create a new attribute for the primary key, for example
ISSUENUM.
ISSUENUM ROLL_NO CODE ISSUE_DATE RETURN_DATE

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 Weak entity:
 It is an entity whose existence depends on some other entity.
The EMPLOYEEADDRESS
entity can be mapped to a
separate table.
ADDRESSID EMPNO CITY
For example:

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 Subtypes and Supertypes:
 A subtype is a subset of another entity.
 A subtype is always dependent on supertype for its existence.
 The primary key of the supertype creates a link between the
supertype and subtypes.

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For example:
Each subtype and
supertype maps to a
separate table.
Supertype
Subtypes

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 An RDBMS identifies and locates rows by value.
 Relational systems require keys that can uniquely identify the rows of a table.
 The various types of keys used in an RDBMS are:
o Primary
o Foreign
o Candidate
o Alternate
o Composite
 Keys

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 Any attribute (or set of attributes) that uniquely identifies a row in a
table is a candidate for the primary key. Such an attribute is called a
candidate key.
 One of the candidate keys is chosen to be the primary key, based on
the familiarity and greater usage.
 Any attribute that is a candidate for the primary key but is not the
primary key is called the alternate key.
 When the key that uniquely identifies the rows of the table is made up
of more than one attribute, it is called a composite key.
 Keys (Contd)

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 Consider the STUDENT table, as shown in the following diagram.
STUDENT# and REGN# are
both individually unique in every
row.
If STUDENT# is chosen as the
primary key, then REGN# is the
alternate key.
Candidate keys
Primary key Alternate key

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 Keys can be simple or composite. A Simple key is composed of a
singe attribute.
 A composite key, on the other hand, comprises two or more attributes.
ACCNUM TRANSDATE TRANSTIME AMOUNT DESCRIPTION
A1101 01/02/2001 12:30 P.M 1000.00 Deposit
A1102 01/02/2001 12:30 P.M 2000.00 Deposit
A1101 02/02/2001 10:30 P.M 3000.00 Deposit
 In the preceding table, assume that only one transaction can take
place for a given account number at a time.
 We can select ACCNUM, TRANSDATE, and TRANSTIME as the
composite key.

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 Consider the table, WORKING HOURS of an employee, as shown in the
following diagram.
EMPLID PROJECTID HOURS
E309 P675 18
E453 P908 5
E334 P876 20
Composite key
Each row can be uniquely identified by a
composite key composed of EMPLID and
PROJECTID.

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