Second Normal Form :

Data is in Second Normal Form if it is in 1NF and every non-key is functionally dependent on the primary key. (An attribute is a non-key if it is not part of the primary key). The purpose of 2NF is to eliminate repeating groups and to ensure that the remaining attributes belong to this entity.

An attribute is functionally dependent on a key if the attribute contains only one value which depends on that key. For example, the attribute SALARY contains only one value which depends on the key NAME. One way to eliminate repeating groups is to create a new attribute (field) for each value expected as shown in following figure. However, this has two disadvantages :

1. It limits number of groups that may be stored.

2. It uses too much space.

If an arbitrary limit of five dependents is made in this example, we can not handle an employee who has six or more dependents. On other hand, if an employee does not have any dependents, the space allocated is wasted.

Third Normal Form (3NF) :

Name Salary Dependent Rama 10,000 Seetha Lava

Kusha Unnormailsed data representing group

Name Salary Dependent 1

Dependent 2

Dependent 3

Rama 10,000 Seetha Lava Kusha

1 NF – Separate entities

Name Salary (Rs.)

Rama 10,000

2 N F -Multiple fields

Seetha Lava Kusha

Srinivas MBA : MIS : CH 4   2009 

116

Data is in Third Normal Form (3NF) if and only if it is in 2NF and every non-key attribute is non-transitively dependent on the primary key. The purpose of 3NF is to ensure that attributes directly belong to the entity.

Transitivity is a mathematical principle that states that if a relation is true between the first value and the second and the third, then the relationship must also be true between the first and the third.

The following are the examples of transitivity : If A < B and B < C, then A < C

If A > B and B > C, then A > C If A = B and B = C, then A = C Or

If A is functionally dependent on B and If B is functionally dependent on C, then A is functionally dependent on C.

For example, an employee record may have the name and salary of the supervisor as attributes. The supervisor’s salary is functionally dependent on the supervisor’s name and the supervisor’s name is functionally dependent on the employee’s name. Therefore, the supervisor’s salary is transitively dependent on the employee’s name. To correct this problem, the attributes directly dependent on the supervisor should kept as a separate entity.

Name Salary Supervisor Sup. Salary

Rama 15,000 NARAYANA 30,000

Krishna 18,000 NARAYANA 30,000

Hari 22,000 NARAYANA 30,000

2 N F but not in 3 N F transitively dependent NAME SALARY

NARAYANA 30,000 Supervisor

NAME SALARY RAMA 15,000 KRISHNA 18,000 HARI 22,000 Separate entities3 N F

Srinivas MBA : MIS : CH 4   2009 

117

Comparison between File Management and Database Management :

File management means traditional approach to managing data stored in files. It involves application programs using input / output routines to open, read, write and close data files. The difference between file management and database management are listed in following table. Neither approach is better than the other. Thus trade offs are involved in selecting an approach.

TOPIC File Management Database Management

Data redundancy High Low

Data independence Low High

Application maintenance Higher maintenance cost Low maintenance cost Integrity control Provided by programmer Provided by DBMS Unanticipated queries A custom program has to

be written

A query language can be used.

Data relationship Handled by application An integral part of DBMS

Overhead Little CPU and storage

overhead

More processing power and storage is needed Database ownership Applications may have

their own private data

All data belongs to the DBMS

Database design More files may be designed as needed

More time and effort is spent to develop database

Database administrator Not needed Needed to coordinate user community.

A computer network is a collection of computers and terminal devices connected together by communication system. The set of computers may include large-scale computers, medium large-scale computers, mini computers and micro-computers.

Types of Networks :-

Based on the structure, the computer networks are divided into four types as : (1) Local Area Networks (LAN)

(2) Wide Area Networks (WAN)

(3) Metropolitan Area Networks (MAN) (4) Storage Area Networks (SAN)

Srinivas MBA : MIS : CH 4   2009 

118

(1) Wide Area Networks (WAN) :-

A WAN covers a large geographical area with various communication facilities such as long distance telephone service, satellite transmission, and under-sea cables. The WAN typically involves best computers and many different types of communication hardware and software. Examples of WAN are interstate banking networks and airline reservation systems. Wide area networks typically operate at lower link speeds (about 1 Mbps).

Following are the salient features of WAN : (i) Multiple user computers connected together.

(ii) Machines are spread over a wide geographic region.

(iii) Communications channels between the machines are usually furnished by third party (a Telephone company, a public data network).

(iv) Channels are of relatively of low capacity.

(v) Channels are relatively error-prone (error rate of 1 in 10⁵ bits transmitted).

(2) Local Area Networks (LAN) :-

LAN covers limited area. A typical LAN connects as many as hundred or so computers that are located in a relatively small area, such as a building or several adjacent buildings. Organizations have been attracted to LAN because they enable multiple users to share software, data, and devices. Unlike WAN which use point – to - point links between systems, LANs use a shared physical media which is routed in the whole campus to connect various systems. LANs use high speed media (1 Mbps to 30 Mbps or more) and are mostly privately owned and operated.

Following are some salient features of LAN : (i) Multiple user computers connected together

(ii) Computers are spread over a small geographic region

(iii) Communication Channels between the machines are usually privately owned.

Channels are relatively high capacity.

(iv) Channels are relatively error free (bit error rate of 1 in 10⁶ bits transmitted) The critical reasons that LAN has emerged as popular are :

1. Security

2. Expanded PC usage through inexpensive workstations 3. Distributed processing

4. Electronic Mail and Message Broadcasting

5. Organizational benefits like cost, maintenance etc.

6. Data management benefits

(3) Metropolitan Area Networks (MAN) :

A MAN is somewhere between LAN and WAN. The term MAN is sometimes used to refer networks which connect systems or local area networks within a

Srinivas MBA : MIS : CH 4   2009 

119

metropolitan area. MANs are based on fiber optical transmission technology and provide high speed (10 Mbps or so) between sites.

A MAN can support both data and voice, cable television networks are examples of MANs that distribute television signals. A MAN just has one or two cables and does not contain any switching elements like WAN.

(4) A Storage Area Network (SAN) : SAN is a dedicated, centrally managed, secure information infrastructure, which enables any-to-any interconnection of servers and storage systems. A SAN :

(a) Facilitates universal access and sharing of resources.

(b) Supports unpredictable, explorative information technology growth.

(c) Provides affordable 24 hours x 365 days availability.

(d) Simplifies and centralizes resource management.

(e) Improves information protection and disaster tolerance.

(f) Enhances security and data integrity of new computing architectures.