Network and database concepts UNIT I CHAPTER 2 MRS.SOWMYA JYOTHI

1. CHAPTER 2
NETWORKS AND
DATABASES
MRS. SOWMYA JYOTHI,
ASSISTANT PROFESSOR,
MANGALORE

2. Computer network is defined as an interconnected collection of
autonomous computers. Two computers are said to be interconnected if they
are capable of exchanging information.
Thus the computer network provides a communication path between the
different computers to share the resources and data with other computers.
A network is a way to connect computers so that they can
communicate, exchange information, and share resources in real
time. Networks enable multiple users to access shared data and
programs instantly. This capability frees individual users from keeping
separate copies of data and programs on their own computers.

3. Each of the devices on the network can be thought of as a node;
each
node has a unique address called IP address.
-Addresses are numeric quantities that are easy for computers to work
with, but not for humans to remember.
Example: 204.160.241.98
-Some networks also provide names that humans can more easily
remember than numbers.
Example: www.google.com, www.javasoft.com, corresponding to the
above numeric address.

4.  Computer networks provide several important advantages.
They are:
1. A computer network provides the means to exchange data among
different parts of the organization. They make the program and data
available to different people within the enterprise.
2. Network permits sharing of resource. This helps in better
utilization of resources.
3. Network supports the critical function of backup.
4. Networking allows a very flexible working environment, wherein
the employees can access the office network from remote places
such from their home or from a different city.

5. Common network services are:
1.File services: Networks provide a very effective method to share files with
different users .The file services include file transfer, file sharing.
2. Shared resources: Network allows us to share expensive peripherals or
devices such as printer, fax etc. Print services provide increased access to
printers and handles simultaneous access.
3. Message Services: Network enables different computers to communicate
with each other with speed and accuracy. The message services include
electronic mail, directory services.
4. Application services: Network allows sharing of applications software.
5. Database Services: Database applications allow users to access
information stored in databases.

6. Network Topology
The way in which devices are interconnected to form a
network is called network topology. Layout of the
network.
Network topologies are categorized into the following basic
types:
1. Bus Topology
2. Ring
3. Star
4. Mesh

7. BUS Topology
 Bus topology is a network topology in which every computer
and network device is connected to single cable. When it has
exactly two endpoints, then it is called Linear Bus topology.
Features of Bus Topology
 It transmits data only in one direction.
 Every device is connected to a single cable

8. Advantages of Bus Topology
1. It is cost effective.
2. Cable required is least
compared to other network
topology.
3. Used in small networks.
4. It is easy to understand.
5. Easy to expand joining two
cables together.
Disadvantages of Bus
Topology
1. Cables fails then whole
network fails.
2. If network traffic is heavy
or nodes are more the
performance of the network
decreases.
3. Cable has a limited length.
4. It is slower than the ring
topology.

9.  In star topology, server is connected to each node
individually.
 Server is also called the central node. Any exchange of
data between two nodes must take place through the
server.
 It is the most popular topology for information and voice
networks as central node can process data received from
source node before sending it to the destination node.
 Can be used with twisted pair, Optical Fibre or coaxial
cable.

10.  Star Topology

11. Disadvantages of Star
Topology
These are the
disadvantages of using
star topology −
1. Long cables may be
required to connect
each node to the server
2. Failure of central node
brings down the whole
network
Advantages of Star
Topology
These are the advantages
of using star topology −
1. Failure of one node
does not affect the
network
2. Troubleshooting is
easy as faulty node can
be detected from central

12. RING Topology
 It is called ring topology because it forms a ring as each
computer is connected to another computer, with the last one
connected to the first. Exactly two neighbors for each device.

13. Features of Ring Topology
 The transmission is unidirectional, but it can be made
bidirectional by having 2 connections between each Network
Node, it is called Dual Ring Topology.
 In Dual Ring Topology, two ring networks are formed, and
data flow is in opposite direction in them. Also, if one ring
fails, the second ring can act as a backup, to keep the network
up.
 Data is transferred in a sequential manner that is bit by bit. Data
transmitted, has to pass through each node of the network, till the
destination node.

14. Advantages of Ring Topology
 Transmitting network is not
affected by high traffic or by
adding more nodes, as only the
nodes having tokens can transmit
data.
 Cheap to install and expand
Disadvantages of Ring Topology
 Troubleshooting is difficult in
ring topology.
 Adding or deleting the
computers disturbs the network
activity.
 Failure of one computer
disturbs the whole network.

15. MESH Topology
 It is a point-to-point connection to other nodes or devices. All the
network nodes are connected to each other.
 There are two techniques to transmit data over the Mesh topology, they
are :
1. Routing
2. Flooding
Features of Mesh Topology
 Fully connected.
 Robust.
 Not flexible.

16. MESH TOPOLOGY

17. Types of Mesh Topology
 Partial Mesh Topology : In this topology some of the
systems are connected in the same fashion as mesh
topology but some devices are only connected to two or
three devices.
 Full Mesh Topology : Each and every nodes or devices
are connected to each other.

18. Advantages of Mesh
Topology
 Each connection can carry its
own data load.
 It is robust.
 Fault is diagnosed easily.
 Provides security and privacy.
Disadvantages of Mesh
Topology
 Installation and configuration
is difficult.
 Cabling cost is more.
 Bulk wiring is required.
Robust- if it performs well against attacks

19.  Network Operating System is a collection of
software and associated protocols that allows a
set of autonomous computers which are
interconnected by a computer network to be used
together in a convenient and cost effective
manner.
 It is a software necessary to control the overall
operations of the network.
 Microsoft Windows Server 2003, Microsoft Windows
Server 2008, UNIX, Linux, Mac OS X, Novell

20. Components of Network Operating System
1. Control Kernel coordinates the various functions and
processes of the network.
2. Network Interfaces provide the low-level subnet protocols the
bridging hardware devices with the NOS.
3. File Systems module controls the methods of storing and
retrieving data from various types of storage systems used in
the network.
4. System Extensions allows the network user to customize the
network.
5. System Services module contains the functions to check such
as system security, system reliability, error conditions and
access violations.

21. Types of network operating systems
The two major types of network operating systems are:
 Peer-to-Peer
 Client/Server

22.  In Peer-to-Peer networking all
computers are considered as
equal. They all have the same
abilities to use the resources
available on the network.
 They do not make use of
centralized server for managing
file or network resources.

23. Advantages of a peer-to-peer
network:
 Less initial expense - No
need for a dedicated server.
 Setup - An operating system
(such as Windows XP)
already in place may only
need to be reconfigured for
peer-to-peer operations.
Disadvantages of a peer-
to-peer network:
 Decentralized - No
central repository for
files and applications.
 Security - Does not
provide the security
available on a
client/server network.

24.  A Client-server network has one or more computers acting
as a server while other computers on the network act as
clients that request the services of server.

26. Advantages of a client/server
network:
 Centralized - Resources and data
security are controlled through the
server.
 Scalability - Any or all elements can
be replaced individually as needs
increase.
 Flexibility - New technology can be
easily integrated into system.
 Interoperability - All components
(client/network/server) work together.
 Accessibility - Server can be
accessed remotely and across
multiple platforms.
Disadvantages of a
client/server network:
 Expense - Requires initial
investment in dedicated
server.
 Maintenance - Large
networks will require a staff to
ensure efficient operation.
 Dependence - When server
goes down, operations will
cease across the network.

27.  Internet: It is the global collection of interconnected
networks. It is an information highway that allows
computer users to share computer equipment, programs,
messages and information available at one site with
others. The Internet is also defined as the network of
networks that connects many LANs and WANs.

28. Advantages
 Internet covers almost every aspect of life, one can think of.
Here, we will discuss some of the advantages of Internet:

29.  Internet allows us to communicate with the people sitting at
remote locations. There are various apps available on the wed that
uses Internet as a medium for communication. One can find
various social networking sites such as:
 Facebook
 Twitter
 Yahoo
 Google+
 Flickr
 Orkut

30.  One can surf for any kind of information over the internet.
 Information regarding various topics such as Technology, Health & Science,
Social Studies, Geographical Information, Information Technology,
Products etc can be surfed with help of a search engine.
 Apart from communication and source of information, internet also serves a
medium for entertainment. Following are the various modes for entertainment
over internet.
 Online Television
 Online Games
 Songs
 Videos
 Social Networking Apps

31. Internet allows us to use many services like:
 Internet Banking
 Matrimonial Services
 Online Shopping
 Online Ticket Booking
 Online Bill Payment
 Data Sharing
 E-mail
 Internet provides concept of electronic commerce, that allows the
business deals to be conducted on electronic systems

32. DATA AND INFORMATION

33. DATABASE
 In a database, even the smallest portion of information
becomes the data.
 A database is an organized collection of data of an
organization.
 Repository of data.
 A database management system (DBMS) stores data in
such a way that it becomes easier to retrieve,
manipulate, and produce information.

34. Characteristics of data in a Database are:
1. Shared:- Data in database are shared among different users and
applications.
2. Persistence:-Data in a database exist permanently .
3. Correctness:-Data should be correct
4. Security:- Data should be protected from Un-Authorized
access.
5. Consistency:- Whenever more than one data element in a
database represents real-world values, the values should be
accurate and consistent.
6. Non-redundancy:- No two data items in a database should
represent the same real world entity.

35. Database Types
Depending on the purpose of use, databases can be classified into following
types:
1. Operational Databases
2. Distributed Databases
3. External Databases

36. 1. Operational Database:
 These databases store detailed data needed to support the business
processes and operations of the e-business enterprises.
 In its day to day operation, an organisation generates a huge amount of data such
as inventory management, purchases, transactions and financials. All this
data is collected in a database which is often known by several names such as
operational/ production database, subject-area database (SADB) or
transaction databases.
 An operational database is important to Organisations as they include the
customer database, personal database and inventory database ie the details of
how much of a product the company has as well as information on the customers
who buy them. The data stored in operational databases can be changed
and manipulated depending on what the company
requires.

37. 2. Distributed Databases:
 Many organisations have several office locations,
manufacturing plants, regional offices, branch offices and
a head office at different geographic locations.
 Each of these work groups may have their own
database which together will form the main database
of the company. This is known as a distributed database.

38. 3. External Database
 An External Database contains information gathered for
use across different individuals or organizations,
either via subscription or freely.
 External databases are accessed online by users to
read privately owned data. The Internet Movie Database is
one of the examples of an external database

39. Database Management System (DBMS)
 A database management system (DBMS) refers to the technology for
creating and managing databases.
 Basically, DBMS is a software tool to organize (create, retrieve,
update and manage) data in a database.
 DBMS = Database + Management System. Database is a collection
of data and Management System is a set of programs to store and
retrieve those data.
 Based on this we can define DBMS like this:
DBMS is a collection of inter-related data and set of programs to
store & access those data in an easy and effective manner

40. Advantage of DBMS
1. Improved data sharing:
 DBMS allows the sharing of database under its control by any number of
application programs or users.
2. Improved data security:
 A DBMS provides a framework for better enforcement of data privacy and security
policies.
3. Better data integration:
Data integrity refers to validity and consistency of data. Data integrity
means that the data should be accurate and consistent.

41. 4. Minimized data inconsistency:
 Data inconsistency exists when different versions of the same data appear in
different places. The probability of data inconsistency is greatly reduced in a
properly designed database.
5. Improved data access:
 The DBMS makes it possible to produce quick answers to ad hoc queries.
6. Improved decision making:
 Better-managed data and improved data access make it possible to generate
better-quality information, on which better decisions are based.
7. Improved Backup and Recovery

42. Disadvantage of DBMS
1. Increased costs:
 Database systems require sophisticated hardware and software
and highly skilled personnel.
 The cost of maintaining the hardware, software, and personnel
required to operate and manage a database system can be
substantial.
2. Management complexity:
 Given the fact that database systems hold crucial company data
that are accessed from multiple sources, security issues must be
assessed constantly.
3. Lower efficiency
4. Qualified Personnel

43. DBMS Architecture
The Architecture of most of commercial DBMS are
available has main three levels:
1. Internal Level
2. Conceptual Level
3. External Level
 These three levels provide data abstraction ;means hide the low level
complexities from end users .
A database system should be efficient in performance and convenient in use.
Using these three levels, it is possible to use complex structures at internal level
for efficient operations and to provide simpler convenient interface at external
level.

45. 1. Internal level:
 This is the lowest level of data abstraction.
 It describes how the data are actually stored on
storage devices.
 It is also known as physical level.
 It provides internal view of physical storage of data.
 It deals with complex low level data structures, file
structures and access methods in detail.
 It also deals with Data Compression and Encryption
techniques, if used.

46. 2. Conceptual level:
 This is the next higher level than internal level of data
abstraction.
 It describes What data are stored in the database and What
relationships exist among those data.
 It is also known as Logical level.
 It hides low level complexities of physical storage.
 Database administrator and designers work at this level to
determine What data to keep in database.
 Application developers also work on this level.

47. 3. External Level:
 This is the highest level of data abstraction.
 It describes only part of the entire database that a end
user concern.
 It is also known as an view level.
 End users need to access only part of the database rather
than entire database.
 Different user need different views of database. And so
there can be many view level abstractions of the same
database.

48. Data Models
A Database model defines the logical design and structure of
a database and defines how data will be stored, accessed
and updated in a database management system.
Data models define how data is connected to each other
and how they are processed and stored inside the system.
The various database models are the following:
 Relational Model
 Entity-Relationship Model
 Hierarchical Model
 Network Model

49. Relational Model
 In this model, data is organised in two-dimesional tables
called relations. The tables or relation are related to each other. All the
information related to a particular type is stored in rows of that table.
Hence, tables are also known as relations in relational model.

50. The highlights of this model are −
 Data is stored in tables called relations.
 Relations can be normalized.
 In normalized relations, values saved are atomic
values.
 Each row in a relation contains a unique value.
 Each column in a relation contains values from a
same domain.

51. Entity-Relationship Model
 Entity-Relationship (ER) Model is based on the notion of real-
world entities and relationships among them. While formulating
real-world scenario into the database model, the ER Model creates
entity set, relationship set, general attributes and constraints.
ER Model is best used for the conceptual design of a database.
ER Model is based on −
 Entities and their attributes.
 Relationships among entities.

53.  Entity − An entity in an ER Model is a real-world entity having
properties called attributes. Every attribute is defined by its
set of values called domain. For example, in a school
database, a student is considered as an entity. Student has
various attributes like name, age, class, etc.
 Relationship − The logical association among entities is
called relationship. Relationships are mapped with entities in
various ways. Mapping cardinalities define the number of
association between two entities.
Mapping cardinalities - one to one, one to many, many to one, many to many

54. Hierarchical Model
 In this model each entity has only one parent but can
have several children . At the top of hierarchy there is
only one entity which is called Root.

56. Network Model
 In the network model, entities are organised in a
graph, in which some entities can be accessed
through several path. In this model data is organised
more like a graph, and are allowed to have more
than one parent node.
 Also, as the data is more related, hence accessing
the data is also easier and fast. This database
model was used to map many-to-many data
relationships.

58. Tasks of Network Operating System
1. Managing the network resources
2. Administration of system users
3. System maintenance tasks such as backup
4. File Management tasks
5. Prioritizing print jobs on the network
6. Monitoring security on network resources
7. Data protection and communications with other networks

59. The Structure of DBMS