1. RDBMS Concepts

RDBMS Concepts

Need for Relational Database Systems

It will be nice if I could use my computer to write

information about all my patients once and retrieve it

anytime I need. I also would like to lock the information

in a secured place.

Why dont you try writing it in a word or a spread sheet document.

Yeah I did try that. But at times I

end up entering the same

information twice!Oh! Then you should use relational

database system- like MS Access!

2

Data important to us must be stored so that we can retrieve it when we need it.

Limitation of file

No mechanism to ensure non-redundant data.

No mechanism to ensure data consistency.

Maintenance of relationship is not possible.

There is no mechanism for a recovery after system crash.

To make the above features work with files, application has to be

written and many may need complex code.

3

As an application programmer my focus should be more on business

aspects of my customer. If I use files to store data, I find that common

tasks like writing programs to store and retrieve related data and maintain

consistency for every application takes most of my time and attention!

We need a mechanism to save, retrieve

and maintain data with minimal effort. In

other words, a prewritten system which

takes care of all of these and gives a

simple interface for the application to

interact with.

4

Activity

How do you think data is arranged in the above picture?

Can you identify the kind data? Is it easy to search and retrieve

data?

Is there anyway you could make lookup more easier?

What have you done to make the data more approachable?

5

It is not just about storing information. It is about how to retrieve information effectively and efficiently. So the way we store the information is directly related to way we retrieve it. The key to this is the way we choose to organize the information.

Relational Database

Relational databases store information in tabular form- in rows and

columns.

Each column has data of same type and the row has data pertaining to

one cause.

A table has many rows of similar type.

The table is also referred to as a relation.

Database is a collection of meaningful and related data.

The software that manages this data is database management system

(DBMS) or database system.

RDBMS (Relational database management system) is a type of DBMS.

Go through the different database

models and differences between them.6

Relational database model was introduced by E. F. Codd, of IBM's San Jose Research Laboratory. For a given DBMS, depending on the structural description of the type of data the database stores (which is called Schema) the model is defined. There are 4 models: Hierarchical Model Data is organized into tree-like structure. Used by the older mainframe database systems like IMS by IBM. Parent-child relationship between the data. 1:N mapping. 2. Network Model Network model is very much like hierarchical model with the exception that it allows a record to have more than one parent N:M mapping (many to many relationship) 3. Relational Model Most database system use this model. The schema for relational model is a table (relation) which has a name, attributes or column or field and a type for each field. Relationship is maintained by the common attributes in the tables. Can be one-one or one to many or many to many. This is what we will be learning in this session.

4. Object Model The new wave of database technologies use Object-oriented data model (OODM).

Relationships

With RDBMS, all types of relationships between entities can be be

realized.

Types of relationship

One to one: Relationship between Employee and Permanent

Address

One to many: Relationship between Customer and Order

Many to Many: Relationship between Customer and Bank

Account

Could you give another example for each of the above

relationship?

7

RDBMS Table Example

Attributes or fieldsStudent

Stud Id Name

1 Raghu R

2 Mary Molle

3 Henry F.Korth

4 Jennifer Wisdom

5 Uma R

Tuples, records or rows

Tables

8

RDBMS Products

Oracle

IBM DB2

MySQL

Ingres

Sybase

MS-SQL Server

MS Access

PostgreSQL

9

Types of database system

Type of user:

Desktop Database

Multi-user Database

Type of location

Centralized database

Distributed database

Distributed database

Transactional or Production DBMS

Data warehousing and decision support system

10

Oracle Database Edition

Oracle Database Standard Edition One

Oracle Database Standard Edition

Oracle Database Enterprise Edition

Oracle Database Express Edition

Oracle Database Personal Edition

Edition that we will be working with

Version 10g Release 2 (10.2)

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Oracle Database Editions (Oracle Database 10g Release 2)

Oracle Database Standard Edition One: Oracle Database Standard Edition One delivers unprecedented ease of use, power, and performance for workgroup, department-level, and Web applications. From single-server environments for small business to highly distributed branch environments, Oracle Database Standard Edition One includes all the facilities necessary to build business-critical applications. Oracle Database Standard Edition : Oracle Database Standard Edition delivers the unprecedented ease of use, power, and performance of Standard Edition One, with support for larger machines and clustering of services with Oracle Real Application Clusters (Oracle RAC). Oracle RAC is not included in the Standard Edition of releases prior to Oracle Database 10g, nor is it an available option with those earlier releases. Oracle Database Enterprise Edition: Oracle Database Enterprise Edition provides the performance, availability, scalability, and security required for mission-critical applications such as high-volume online transaction processing (OLTP) applications, query-intensive data warehouses, and demanding Internet applications. Oracle Database Enterprise Edition contains all of the components of Oracle Database, and can be further enhanced with the purchase of the options and packs described in Chapter 2, "Options and Packs". Oracle Database Express Edition: Oracle Database Express Edition (Oracle Database XE) is an entry-level edition of Oracle Database that is quick to download, simple to

install and manage, and is free to develop, deploy, and distribute. Oracle Database XE makes it easy to upgrade to the other editions of Oracle without costly and complex migrations. Oracle Database XE can be installed on any size machine with any number of CPUs, stores up to 4GB of user data, using up to 1GB of memory, and using only one CPU on the host machine. Support is provided by an online forum. Oracle Database Personal Edition : Oracle Database Personal Edition supports single-user development and deployment environments that require full compatibility with Oracle Database Standard Edition One, Oracle Database Standard Edition, and Oracle Database Enterprise Edition.

Oracle Application Architecture

Client-Server Architecture

Client is the front-end that interacts with the user

Server is the backend interacts with the Oracle

Database software and handles concurrent requests

Network

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Client takes the request from the end user, sends the request to the server, gets the data from the server and presents in the form that end user wants to see.

Database design- steps

Requirement Analysis

Conceptual Database Design : ER Diagram

Logical Database Design : Converting ER Diagram into RDBMS tables

etc.

Additional design components like views, stored procedures, triggers

etc.

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ER Model

ER data model allows us to conceptually understand the data of the real

world that we intent to store them.

This model is realized by diagrammatically representing the collection

of entity and their relationship.

There are two notations for entity relationship diagram (ERD):

Chens notation

Crows foot notation.

As stated earlier, this is done in conceptual database design phase.

A data dictionary is built to explain the details of the entities and

attributes that is used in the ER diagram.

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Defining Entity

Entity: It is an object that is distinct and unique. Examples: a

student, a an employee , a college etc.

Entity set: A collection of similar entities is entity set. Examples :

Students, Colleges

Attributes: Properties that describe an entity is attribute. All

entities in the entity set have same attributes (but the values of

the attribute may be different). For example, a student will have

registration number, name and address as attributes.

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Primary Key

A minimal set of attributes that uniquely identifies an entity is called a

candidate key.

An entity can have many candidate keys. For example, for a student

entity, if we assume that students have unique names. In that case both

registration number and name are candidate keys.

One among the candidate keys is chosen to be a primary key. A primary

key should not be null.

A composite key is a primary key with more than one attribute.

A super key is a set of attributes which contains the primary key.

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Activity

List out the entities for a hospital database.

List out the attributes for each entity

Identify the primary key.

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Notations in ER diagram

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Entity Set

Attribute

Relationship

Representing an entity in Chens notation

Students

regNo

name

address

Courses

streamId

title

noOfSems

Entity Set

Attributes

Primary key

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Activity

Represent the hospital database entities in the form of ER diagram.

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Relationship

Relationship is the association between entities or entity sets. For

example between two entities student and course, the relationship is

a course enrolls for many students.

Relationships may or may not also have attributes. For example, if

we were to maintain enrollment date, then the relation enrolls will

have an attribute enrollment-date.

Relationship set is a collection of similar relationships.

Types:

Binary

Ternary

Unary

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Binary Relationship One to One

Subject Is Taught Teacher

teacherId

nameaddresssubId

title

1 1

Relationship Set

Mapping/Connectivity

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Binary Relationship One to Many

Courses Have Students

regNo

nameaddress

streamId title

noOfSems

1 N

Relationship Set


23

Binary Relationship Many to Many

Customer Bank Account

acctNo

acctTypebalance

custId name

address

M N


owns

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Relationship with attributes

Courses Have Students

regNo

nameaddressstreamId

title

noOfSems

1 N

Relationship Set

enrollment-date

Attribute of relationship

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Activity

Identify binary relationships between the entities of hospital

database and represent them in the ER diagram.

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Cardinality

Courses Has Students

regNo

nameaddressstreamId

title

noOfSems

enrollment-date

(1,35)(1,6)

Cardinality

Cardinality is used to specify number of entity occurrences with one

occurrence of related entity.

A course can have a minimum of 1 and a maximum of 35 students. A

student can take a maximum of 6 and a minimum of 1 course.

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Example of a Ternary relationship

Employees DepartmentsWorks-In

Location

dateOfJoining

name

deptId

name

empId

address capacity

locId

N M

P

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Example of a Unary relationship

CustomercustId

name

address

referred

byN

1

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Key Constraints on relationship

Consider a restriction where a student can join only one course. This is an

example of a key constraint.

In the below diagram the directional arrow ensures that there is only one

instance of student in the relationship set Has. In other words, given a

student, has relationship can be uniquely determined.

Courses Has Students

regNo

name

address

streamId

title

noOfSems

1 N

enrollment-date

Directional arrow

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Activity

What is the relationship between customer and the plot he/she

buys?

Draw an ER diagram to represent the relationship.

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Participation constraints

Total participation: If all entities in an entity-set need to be in the

relationship set then the entity is in total participation with respect to

relationship.

Example: Every employee works in at least one department. Each

department has at least one employee. Therefore both Employee and

Department entities in Works-In relationship is total.

Partial participation: A participation that is not total is partial .

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Example of a total participation

Employees DepartmentsWorks-In

location

dateOfJoining

name

deptId

name

empId

address capacity

locIdIndicates total

participation

or

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Modeling Attributes

Single valued attributes the examples that we have seen so far

consisted of single value attributes.

Composite Attribute

Multi-Valued Attribute

Derived Attribute

34

Composite Attribute

A composite attribute is an attributes that is made up of more than

one attribute.

For example address can be thought of as having more than one

attribute.

address

house number street number

area

districtstate

country

Employees

composite attribute

35

pin

Multi-Valued Attribute

A multi-value attribute is an attribute which can have multiple

values.

phone_numbers Employees

multi-valued attribute

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Derived Attribute

A derived attribute is an attribute whose value is determined or computed

using existing values of the other attributes (or otherwise also called

stored attribute).

While the value of the composite attribute for a row is computed as

concatenation of the values of a set of attributes of the same row, the

derived attribute can be calculated based on values of attributes in

multiple rows also (example sum of gross salary of all entities in

Employee entity set).

37

Employee

deductionsgross_salary net_salary

derived stored

attribute

Weak Entities

A weak entity is an entity that cant be uniquely identified by its own

attributes alone, and therefore must use as its primary key both its

own attributes and the primary key of an entity it is related to.

In other words, a weak entity cannot exist without the entity it is

related to (owner entity).

The relationship between owner entity and weak entity is one-to-

many.

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Orders Order-Itemscontains

A weak entity set diagram

itemNocustId

orderDateorderNo

noOfPieces

partial key

1 n

contains

Order-Items

or

or

Identifying

relationship

The entity will be in total participation

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Assume a shopping application. A customer orders for many items. We have 2 entities to maintain customer order. Orders entity: records the order details like order number, order date and customer id Order-Items: records the items pertaining to the order. Order-Items entity is a weak entity.

Hierarchy

The entities can be classified as general type and specific type.

IS-A relationship.

For example, an Employee can be a programmer or a manager.

Employee

nameempId

IS-A

Programmer Marketing Manager

Current-Project

Main-Role

area

num-of-contracts

specia

lizatio

ngenera

lization

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Redundant relationship problem

Consider a relationship where employee works on an assignment and

may use machinery.

Employee

namejoiningDate

works Project

uses Computer

machineID

purchaseDateredundant relationships

empId

hours

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Aggregation

Solution is to use aggregation. Aggregation is a relationship between

collection of entities and relationships.

Aggregation allows us to indicate that a relationship set participates

in another relationship set.

Use aggregation when we need to have a relationship among

relationship.

42

Employee

namejoiningDate

works Project

uses MachinerymachineID

purchaseDate

aggregation

empId

hours

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Exercises

1. Draw an E-R diagram for the following application.

a. A training institute conducts up to 6 courses.

b. A course can have up to 30 students.

c. A student can enroll for a particular course only once. However a

student can enroll for any number of courses. The date of enrollment of

the course is also maintained.

d. A course is described by its course-id, title and duration, course-id

being the primary key.

e. A student is described by stud-id, name and address (house number,

street or area, town, dist , city state). The stud-id is the primary key.

f. There is no student who has not taken any course. There are however

courses for which there are no students. (30 mins)44

2. Draw an E-R diagram for the following application.

a. A company maintains details of its Employees like empId, name, date

of birth)

b. Each Employee works for a single department.

c. There are two types of employee- Contract and Permanent. Contract

employees work for a period of time and are given temporary id. They

are paid in per day basis. Permanent employees are paid every month

and they have permanent id.

d. Department is identified by deptId, name.

e. Each department has one of the employees as manager.

f. Company also needs the details of all the Employees Bank accounts.

g. Bank Account details are acctNumber, Type of account, Name of the

Bank and Branch.

(30 mins)45

3. Draw an ER diagram for a bus company with following specifications:

a. A Country Bus Company owns a number of busses.

b. Each bus is allocated to a particular route, although some routes may

have several busses.

c. Each route passes through a number of towns.

d. One or more drivers are allocated to each stage of a route.

e. A stage corresponds to a journey through some or all of the towns on a

route.

f. Some of the towns have a garage where busses are kept and each of the

busses are identified by the registration number and can carry different

numbers of passengers, since the vehicles vary in size and can be single or

double-decked.

g. Each route is identified by a route number and information is available on

the average number of passengers carried per day for each route. 46

4. Draw an ER diagram for application recording information about

magazines, writers, and subscribers, including:

a. For each magazine, its name, its writers, its editor, and the cities to

which it is delivered are to be maintained.

b. For each writer, their id, name is to be maintained. (Note: a writer

can write for more than one magazine, but can only edit, at most, one

magazine.)

c. For each subscriber, their name, favorite writers, city or residence,

and what magazines they receive are to be maintained.

d. For all entities and relationships, select and specify keys.

47

Activity

What are the problems if the data is repeated?

Roll Number Name Degree

20103001 V. Ravichandra M.C.A

20103002 Usha Kritilal M.C.A

20103003 Samkit Verma M.C.A

20103001 V. Ravichandra M.C.A

20103004 Guru Murthy M.C.A

20103007 Jaya R M.C.A

20105009 Vivek Sahoo B. Tech

20105007 Booby Sharma B.Tech

20103004 Guru Murthy M.C.A

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Problems with a bad database design

Redundant Storage

Update Anomalies

Insertion Anomalies

Deletion Anomalies

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Definition

First proposed by Dr. Codd.

Normalization is the process of breaking down a relation schema

into smaller relations in order to achieve good database design.

To achieve good design, several step by step decomposition rules

are laid out in the form of NORMAL FORMS.

There are 6 Normal forms.

For most relational schema, good design is attained at 3 NF itself.

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Take care : While normalizing we also pay attention to two important aspects: Lossless Join: There should be no loss of information when tables are split. Dependency Preservation: The dependency between the attributes must be preserved.

1 NF

First Normal Form

There are no duplicated rows in the table.

Each cell is single-valued (i.e., there are no repeating groups or arrays).

Entries in a column (attribute, field) are of the same kind

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Un-normalized data

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Stud

Id

Stud

Name

Course

No

Course

Name

Staff

ID

Staff

Name

PaperNo Subject

Name

Grade

1 Sita 1 JEE 2 Preeti 1 Java A

2 JEE 2 Web A

2 Jay 2 .NET 1 Guru 1 C# B

3 Mani 3 A

ASP.NET A

4 Kim 4 SAP 3 Ravi 3 ABAP B

5 Ram 5 A

Into 1NF

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Stud Id

Stud

Name

Course

No

Course

Name

Staff ID Staff

Name

PaperNo Subject Name

Grade

1 Sita 1 JEE 2 Preeti 1 Java A

1 Sita 1 JEE 2 Preeti 2 Web A

2 Jay 2 .NET 1 Guru 1 C# B

3 Mani 3 .NET 1 Guru 1 C# A

3 Mani 3 .NET 1 Guru 2 ASP.NET A

4 Kim 4 SAP 3 Ravi 3 ABAP B

5 Ram 4 SAP 3 Ravi 3 ABAP A

Here primary key is a composite key

2 NF

Second Normal Form:

A table is in 2NF if it is in 1NF and if all non-key attributes are fully

functionally dependent on all of the key attributes ( or prime

Attribute).

Key attribute or Prime attribute is an attribute that is a part of any

candidate key.

Functional Dependency: Let A and B be two attributes or set of

attributes. B is functionally dependent on A if Bs value is determined

by As value.

A is the determinant.

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Full Functional Dependency

Full Functional Dependency (AB) : B is fully functionally dependent

on A, if on removing any one of the attribute x from A, B cannot be

determined.

If B can still be determined on removal of x from A, the B is partially

dependent A.

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Into 2 NF

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Stud Id

Stud

Name

Course

No

Course

Name

Paper

No

Subject Name

Grade

1 Sita 1 JEE 1 Java A

1 Sita 1 JEE 2 Web A

2 Jay 2 .NET 1 C# B

3 Mani 3 .NET 1 C# A

3 Mani 3 .NET 2 ASP.NET A

4 Kim 4 SAP 3 ABAP B

5 Ram 4 SAP 3 ABAP A

Student

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Course

No

Course

Name

Staff

ID

Staff

Name

PaperNo Subject

Name

1 JEE 2 Preeti 1 Java

1 JEE 2 Preeti 2 Web

3 .NET 1 Guru 1 C#

3 .NET 1 Guru 2 ASP.NET

4 SAP 3 Ravi 3 ABAP

Course

3 NF

Third Normal Form

A table is in 3NF if it is in 2NF and if it has no transitive

dependencies of a non-key attribute on the primary key.

Transitive dependencies (AB, BC):

Let A, B and C be three attributes or set of attributes. If B is

functionally dependent on A and C functionally dependent on B

(in other words C is indirectly dependent on A) then C is

transitively dependent on A.

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Into 3NF

Transitive dependency:

Student table

StudID Course No

Course No Course Name

Course table

CourseID StaffID

StaffIDStaffName

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Do we have transitive dependency between courseID , PaperNo and Subject Name

No

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Stud Id

Stud

Name

Course

No

Paper

No

Grade

1 Sita 1 1 A

1 Sita 2 2 A

2 Jay 2 1 B

3 Mani 3 1 A

4 Kim 4 3 B

5 Ram 4 3 A

Course

No

Paper

No

Subject Name

1 1 Java

2 2 Web

2 1 C#

3 2 ASP.NET

4 3 ABAP

Course

No

Course

Name

1 JEE

2 .NET

3 .NET

4 SAP

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Course

No

Course

Name

Staff

ID

PaperNo Subject

Name

1 JEE 2 1 Java

1 JEE 2 2 Web

3 .NET 1 1 C#

3 .NET 1 2 ASP.NET

4 SAP 3 3 ABAP

Staff

ID

Staff

Name

2 Preeti

1 Guru

3 Ravi

Boyce-Codd Normal Form

A table is in BCNF if every determinant in the table is a candidate

key.

This happens when non-key attribute is a determinant of a key

attribute.

If the table has only one candidate key, then BCNF and 3 NF are

same. Hence BCNF is sometimes referred to as a special case of 3

NF.

However a table that is in 3NF may be in BCNF.

BCNF comes into picture only where there are two candidate keys.

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Activity

Tom has to compute the result based on the Grade. (A and B are

Pass, C is fail)

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Stud Id

Stud

Name

Course

No

Paper

No

Grade Result

1 Sita 1 1 A

1 Sita 2 2 A

2 Jay 2 1 B

3 Mani 3 1 A

4 Kim 4 3 B

5 Ram 4 3 A

TOM: Read Grade A

JACK: Read Result

Result is null,

So update Grade to C

TOM: Update the Result to Pass

Can you identify the problem here? How do you propose to make sure that problem

does not occur again?

Problems with simultaneous access to same data

Activity

Alice and Akshay have a joint account in ABC Bank. The account

has Rs.5000. Alice is in London visiting her parents and Akshay is at

work. Both are in need for some money and they withdraw 3000

rupees simultaneously.

Do you foresee any problems that could happen if bank has not

dealt with this situation?

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Problems with concurrency

Lost update

Transaction A reads the data with the intention of updating it.

Meanwhile another transaction B has already changed the data in

between the read and update of transaction A.

Dirty read

transaction A reading data that has not yet been committed by

transaction B

Non repeatable read

Transaction A tries to read the data it has already read and now finds

that the data in the row(s) is/are changed or deleted by another

transaction B.

Phantom records

Transaction A executes the same query twice to find that the both the

queries return different result set. 65

Transaction Processing

Logical unit of program execution that takes a database from one

consistent state to another consistent state.

A transaction is a collection of SQL statements that are either

committed completely or rolled back completely even if one statement

in the transaction fails to execute.

Oracle database engine creates unique transaction ID for all

transactions.

A transaction must comply to ACID properties

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Concurrency techniques: Locking Time stamping

ACID properties

Atomicity

Either all the sql statements that is part of the transaction, are

committed or none

Consistency

The state of the database before and after the execution of

transaction must be consistent

Isolation

Even though the transitions are executing simultaneously, the result

of the simultaneous execution must be as if they are run in isolation

or one after another.

The result of the transaction must be visible only after the transaction

has been committed.67

Atomicity Example: if a transaction starts updating salaries for all the 1000 employees and database crashes after 999th record, then the database rolls back the all the changes to 1000 records. Consistency Example, transfer of money from one account to another account must not stop with debiting the amount in one account and not crediting in another. Isolation In the 1st example, imagine what would happen if the an employee sees his salary has increased and his colleague does not see it being reflected.

Durability

Changes made by the committed transactions which are

temporarily held in the current in-memory database image are

made permanent by recording them in the hard disk. Even while

changes are being made, system crashes occur, the recovery

mechanism ensure that the result of the transaction is not lost.

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Exercises

1. Normalize the given table to 2NF and 3NF.

Happy Home Super market deals with groceries, household items,

stationary products and gift items. They have announced a summer

mela where, for every customer who holds a membership with

Happy Home, any three items can be taken for free. The total price

of the three items should be equal to or below Rs.1000. They record

details of these free products given to their member customers in a

table as below.

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15 mins

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2. Normalize the given table ensuring no data loss and data redundancy.

15 mins

3. Good Work Cooperation is the Computer Programming Services industry

in DALLAS, TX. It has offices throughout North and South India.

Employee fills in the following details at the time of joining : Name, Phone

number, Hiredate, Salary, Commission and Address. He/She is given a

unique ID.

Employee is then allocated a project under a LOB. He/She reports to a

Reporting Manager who is also an employee.

Projects have a unique id, name, duration (in months), Project Manager

who is an employee. Every project is under a LOB.

Every LOB has a unique ID, Name and multiple locations(address) from

where they operate.

Design an appropriate set of Normalized Relations to represent this

information

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1. RDBMS Concepts

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