Tuesday, 2 June 2020

2075-Solution of Computational Course (Computer Science) : Long Answer Question

Long Answer Question


Attempt any TWO questions.

1) How authentication and authorization ensure some level of security in computers? Explain about the various authentication systems used in computer security? (4+6)

Ans:
Authentication and authorization ensure security in computer. It is because it helps to,
  1. Validates user’s credential such as username and password to identify user.
  2. Determines who can access to the data and materials.
  3. Enables organizations to keep their networks secure by permitting only authenticated users (or processes) to access its protected resources
  4. Prevent a user from accessing an account that isn’t theirs
  5. Restrict free accounts from getting premium features
  6. Ensure internal accounts only have access to what they need
  7. To prevent loopholes from where hackers get their access to server
  8. Notify users of any suspected malicious or unusual activity

The various authentication systems used in computer security are:
1) Password based authentication:
Passwords are an example of an authentication mechanism based on what people know. The user supplies a password and the computer validates it.
A password is an information associated with an entity that confirms the entity’s identity. It can be sequence of characters and digits or sequence of words such as phrases. Password can be used in storage in many ways such as in plain text form, in encrypted form or in the form of hash value of password.

2) Smart card based authentication:
A smart card is a small plastic cards, about the size of a credit card containing an embedded microchip that can be programmed to store specific user authentication information.
Smart cards help to eliminate the threats of hackers stealing stored or transmitted information from a computer. The information is processed on the smart card, so the authentication information is never transmitted to another machine.

3) Biometric based authentication:
It is a type of a system that relies on the unique physiological or behavioral characteristic of individuals to verify for secure access t electronic systems.
Some of the widely used physiological or behavioral characteristics are faces, fingerprints, voices, DNA structure, etc. Among all, biometric is the most secure and convenient authentication tool. It can’t be borrowed, stolen or forgotten but demerits are they are slow, intrusives and expensive.


2) How do you mean by database schema and database instance? Differentiate between the centralized, client/server and distributed database architectures. (3+7)

Ans:
Database Instances and Schema:
Overall structure of the database is is called database schema. For example, employee information in a company database may be stored in a relation with the following schema. Employee ( Eid:string, Ename:string, Address:string, Salary:integer ). Once created, database schema is not expected to change frequently. Database administrator is responsible for creating, deleting and modifying database schema.
The collection of information stored in the database at a particular moment is called an instance of database.It is the actual content of the database at a particular point. Database instance changes frequently with every insertion, deletion and update operations performed in data stored in a database.

The differences between the centralized, client/server and distributed database architecture are:
Centralized
Client/Server
Distributed
Data is stored only on one site.

Data is stored in different sites.
Data stored in single computer can be used by multiple users.
Client/server architecture shares the data processing chores between a server (high-end workstation) and clients (personal computers).
Data is stored over different sites which are connected with each other.
If centralized system fails, then the entire system is halted.

If one of the system fails, then user can access the data from other sites.
Centralized DBMS is less reliable and reactive.

Distributed DBMS is more reliable and reactive.
Centralized DBMS is less sophisticated.

Distributed DBMS is more sophisticated.

3) How spatial data is represented in GIS? Discuss about the data source and data input techniques in GIS. (3+7)

Ans:
Spatial data is represented in GIS as vector data and raster data model. Spatial data comprise the relative geographic information about the earth and its features. A pair of latitude and longitude coordinates defines a specific location on earth. Spatial data are of two types according to the storing technique, namely, raster data and vector data.
Raster data are composed of grid cells identified by row and column. The whole geographic area is divided into groups of individual cells, which represent an image. Satellite images, photographs, scanned images, etc., are examples of raster data.
Vector data are composed of points, poly lines, and polygons. Wells, houses, etc., are represented by points. Roads, rivers, streams, etc., are represented by poly lines. Villages and towns are represented by polygons.

Raster 
Vector
1) Simple data structure.
  1. More complex structure.
2) Overlay operations are easily and effectively implemented.
2) Are more difficult to implement.
3) High spatial variability is efficiently represented in a raster format.
3) Representation of high spatial variability is inefficient.
4) Raster data structure is less compact.
4) Vector provides more compact data structure.
5) Topological relationships are more difficult to represent.
5) Provides efficient encoding of topology.
6) Manipulation and enhancement of digital images can be effectively done.
6) Cannot be effectively done in the vector domain.

Data Source
Two types of data are input into a GIS, spatial and attribute data. The data input process is the operation for encoding both types of data into the GIS database formats. A wide variety of the data source exists for both spatial and attribute data. 
The most common general source for spatial data are:
  1. Analogue maps
  2. Imageries
  3. Global positioning system
  4. Statistical data
  5. Existing digital data files
Existing hardcopy maps provide the most popular source for GIS project.

Data Input Techniques
The input of attribute data is usually quiet simple. The discussion of data input techniques will be limited to spatial only. There are at least 4 basic procedures for inputing spatial data in GIS.
  1. Manual Digitizing - While considerable work has been done with newer technologies, the overwhelming majority of GIS spatial data entry is done by manual digitizing.
  2. Automatic Scanning - A variety of scanning device exists for the automatic scanning or capture of spatial data. We can capture spatial features from a map at a rapid rate. Large data capture work are done using scanning technology.
  3. Coordinate Geometry - The input of spatial data involves the calculation and entry of coordinate geometry (CoGo) procedures. This input technique is very costly and labor intensive and is rarely used for natural application in GIS.
  4. Conversion of Existing Digital Data - Conversion of existing digital data is  being increasingly popular. A variety of spatial data including digital maps are openly available from a wide range of government and private sources.  
Posted by at

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)