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Assignment on DBMS submitted by Nirmal Chaulagain to Binaya sir.
1. What do you mean by Database and DBMS? Give the advantages, disadvantages and purpose of
DBMS.
=> Database is the organized collection of the related data, whereas DBMS is the general purpose
software which is used to create and maintain the database.
Advantage of DBMS
*sharing of data
*reduce data redundancy
*Independence of data
*Data security can be improved
Disadvantages of DBMS
*Requires technical and database knowledge.
*Costly, required highly skilled manpower.
*Data will be lost in case of crash of hardware of software.
Purpose of DBMS
*To provide storage area for huge amount of data.
*For easy access of data for end users
*To make latest modification on database.
*To allow multiple user to be active at the same time.
2. What is Data model? Explain the various types of Database model with their advantages and
disadvantages.
=> Data model is a set of conceptual tools for describing data and their relationship.
Types of data model:
a) Hierarchical model
Advantage
-In this model records are very efficient in handling one to many relationships.
-searching of record is very fast and easy if parent is known.
Disadvantage
-But if parent is not known then searching of record may not be fast.
b) Network database model
Advantage
-this model is efficient in handling many relationships.
-this model is able to model complex relationships and represents semantics of add/delete on the
relationship.
c) Relational database model
Advantage
-it can be used to relate the data of one table to the data of another table.
-it reduces data redundancy
-in this model normalization is possible
Disadvantage
-Too many rules are implemented while designing database which makes it less user friendly.
d) Physical data model
Advantage
-this model can be used to know, how data is stored in computer and the physical components required
to access and retrieve data.
e) E-R (Object oriented database) model
- It consist of real time objects where each object contains data and member functions which
can be used to manipulate data
3. What is data abstraction? Explain the different level of data abstraction in brief.
Ans:-The main purpose of DBMS is to provide the user with the abstract view of database i.e. system
does not provide all the details of the data; rather it hides the details how data is stored & maintained.
Such properties of DBMS are called Data Abstraction.
Different levels of data abstraction are explained below in brief:
a) External View / Level / Schema or User View / Global View
- Highest or Top level of data abstraction. This level is concerned with the user. There can be n number
of external views for database where n is the number of users.
b. Conceptual View
- This level is in between the user level and physical storage view. It hides the details of physical storage
structures and concentrates on describing entities, data types, relationships, user operations, and
constraints.
c. Internal View / Physical View
- It is the lowest level of data abstraction. It is close to the physical storage method. The internal view is
the view that tells us what data is stored in the database and how. At least the following aspects are
considered at this level: Storage allocation, Access paths etc.
4. Define the term Instances and Schema. Design Schemes for Library management system.
Ans:-Database Schema is the overall design and description or specification of a database. It includes
descriptions of the database structure and the constraints that should hold on the database.
Schema diagram for library management system is shown below:
5. What is data independence? Compare physical data Independence with Logical data independence.
Ans:- Data independence is an ability to modify schema definition in one level without affecting a
schema definition in next level.
Comparison between physical data independence with logical data independence are
shown below:
(a) Whenever, the changes are made at the internal level without affecting the above layers, it is known
as physical data independence. E.g. The location of the database, if changed from C drive to D drive will
not affect the conceptual view or external view as the commands are independent of the location of the
database
And whenever, there is a change or modification at the conceptual level without
affecting the user level or external level, it is known as logical data independence E.g. the name
field in conceptual view is stored as first name, middle name and last name whereas in external
view, it remains to be as a single name field. Change the conceptual schema without having to
change the external schemas and their associated application programs.
(c) Physical data independence is concerned with storage of the data.
Whereas, logical data independence is concerned with the structure of the data or changing the
data definition.
(d) Physical data independence is concerned with the internal schema.
Logical data independence is concerned with the conceptual schema.
6. Who is Database Administrator? Explain the roles of DBA in brief.
Ans:- DBA is a chief person in an organization who is responsible for maintaining RDBMS in an
organization. As database administrators are the chief person, he has to play various roles for defining
internal or external schema. He also has to insert, update and monitor DBMS server. Another important
role is he/she has to perform backup task and recovery of data.
7. Who are the database users? Write the functions of different database users.
-> Database Users are Naïve users, Application programmers and sophisticated
Users who perform the task related to database.
Functions of different database users are listed below:
(a) Naïve users: - use the application interface for various data entry functions.
(b) Application programmer: - design an application program or interface.
(c) Sophisticated users:-Looks for storing, retrieving, and managing records from database.
8. Write short notes on 1-tier, 2-tier and n-tier application architecture.
Ans:a)Centralized DBMS Architecture (1-tier):
It combines everything into single system including- DBMS software, hardware, application
programs, and user interface processing software. In 1-tier user can still connect through a remote
terminal – however, all processing is done at centralized site.
b) 2-tier client server architecture:
This architecture consists of client and server.
Clients /users can access the specialized servers as needed. Client provides GUI
and local processing and also provide appropriate interfaces through a client software module to access.
Server is of different types like Print server, File server, DBMS server, Web server and Email server
Where DBMS server provides database query and transaction services to the clients
c) Three-tier client server Architecture
This architecture is common for Web applications. Three-tier Architecture:
-Enhances Security:
-Database server only accessible via middle tier
-Clients cannot directly access database server
9. Write the role of the followings:(a) Storage manager
They test for the integrity constraints and check the authority for users to access data. They also ensure
that data remains consistence despite system failures and concurrent transactions proceed without any
conflicting. And they are also responsible for allocating of space on disk storage and are also responsible
for fetching data from disk storage into main memory and deciding what data to cache in memory.
(b) Buffer manager
Buffer manager is responsible for fetching data from disk storage into main memory and deciding what
data to cache in memory.
The buffer manager reads disk pages into a main memory page as needed. Buffer manager is used by
(the code for) access methods, heap files, and relational operators to read / write /allocate / de-allocate
pages. The Buffer Manager makes calls to the underlying DB class object, which actually performs these
functions on disk pages.
(c) Disk manager
Disk manager is responsible for managing the physical structure of database. Disk is generally
use for the storage of data which will be managed by disk manager.
(d) Query manager
It translates DML statements into low level statements that the query evaluation engine
understands. It also converts DML statements in an application program into normal procedure calls to
provide appropriate code. Also interprets DDL statements and records them in a set of table containing
meta-data. And finally generate query for database users and DBA.
10. Explain database system structure and it’s all component in brief.
Ans:- A database system structure is related with the division of database system into modules on the
basis of their function. Different components of database structure are:a) Database users:
It is divided into four types:Application programmers: Application programmers are those who prepares application program. It
works on the data for creating new information, retrieving information, deleting existing information.
Sophisticated users: Those people who interact with the system without writing programs are called
Sophisticated users. They form their requests in a database query language. Each such query is
submitted to a query processor whose function is to take a DML statement and break it down into
instructions which are understood by that the database manager.
Specialized users: They write specialized database applications that do not fit into the traditional data
processing framework. Computer-aided design systems, knowledge- base and expert systems, systems
that store data with complex data types etc are the examples of such application.
End users: Those who interact with the system by invoking one of the permanent application programs
that have been written previously are called end users. For this class of user retrieval is the most
common function. Naive users: They are interact with the system by using permanent application
programs.
b) Query processor:
The query processor provides the facilitites to access data. Some components of query
processor are:
* DDL Interpreters
It interprets DDL statements and records the definition in the data dictionary.
* DML Compiler
It translates the DML statements in a query language into an evaluation plan
consisting of low-level instructions that the query evaluation engine understands.
* Query Evaluation Engine
. It executes low level instructions generated by the DML compiler.
c)
Storage manager :
It is a program module which provides the interface between the low-level data stored in the
database and the application programs and also the queries submitted to the system.It translates DML
statements into low level file system commands. It is also responsible for the interaction with the file
manager. Thus the storage manager is responsible for storing, retrieving, and updating data in the
database. The storage manager components are Authorization and integrity manager, Transaction
manager, File manager and Buffer manager.
Authorization and integrity manager tests for the integrity constraints and checks the authority for
users to access data.
Transaction manager ensures that data remains consistence despite system failures and concurrent
transactions proceed without any conflicting.
File manager manage the allocating of space on disk storage and the data structure used to represent
information stored on disk.
Buffer manager is responsible for fetching data from disk storage into main memory and deciding what
data to cache in memory.
d) Disk manager:
It is the part of operating system of the host computer and all physical input and output operations are
performed by it. It is also responsible for managing the physical structure of database. It transfers the
block and page requested by file manager so that the latter need not be concerned with the physical
characteristics of underlying storage media.
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