Unit- I
Overview
of
Database
Management System: Introduction,
file-based system, Drawbacks of file-Based
System ,Data and information, Database, Database management System,
Objectives of DBMS, Evaluation of Database management System,
Classification of
Database Management
System, DBMS Approach, advantages of
DBMS, Anis/spark Data
Model, data models, Components
and Interfaces of Database Management
System. Database Architecture, Situations where DBMS is not Necessary,
DBMS Vendors and Their Products.
Q) Define Data and Information.
A) Data and Information
Data are raw facts that constitute building
block of information. Data are the heart of the DBMS. Data will not convey useful
information. Useful information is obtained from processed data.
Data are a representation of facts, concepts,
or instructions in a formalized manner suitable for communication,
interpretation, or processing by humans or automatic means.
The data in DBMS can be broadly classified
into two types, one is the collection of information needed by the organization
and the other is “metadata” which is the information about the database.
Data are the most stable part of an
organization’s information system. A company needs to save information about
employees, departments, and salaries. These pieces of information are called
data. Generally, we perform operations on data or data items to supply some
information about an entity. For example library keeps a list of members,
books, due dates, and fines.
Q) Explain briefly about Database.
A) Database
A database is a well-organized collection of
data that are related in a meaningfulway, which can be accessed in different
logical orders. Database systems are systems in which the interpretation and
storage of information are of primary importance. The database should contain
all the data needed by the organization as a result, a huge volume of data, the
need for long-term storage of the data, and access of the data by a large
number of users generally characterize database systems. The simplified view of
database system is shown in Fig. 1.1.
From this figure, it is clear that several
users can access the data in an organization still the integrity of the data
should be maintained. A databaseis integrated when same information is not
recorded in two places.
Q) Write a note on Database Management System
A) Database Management System:
A database management system (DBMS) consists
of collection of interrelated data and a set of programs to access that data.
It is software that is helpful in maintaining and utilizing a database.
A DBMS consists of:
– A collection of interrelated and persistent
data. This part of DBMS is referred to as database (DB).
– A set of application programs used to
access, update, and manage data.
This part constitutes data management system
(MS).
– A DBMS is general-purpose software i.e., not
application specific. The same DBMS (e.g., Oracle, Sybase, etc.) can be used in
railway reservation system, library management, university, etc.
– A DBMS takes care of storing and accessing
data, leaving only application specific tasks to application programs.
DBMS is a complex system that allows a user to do many things to data as
shown in Fig. 1.2. From this figure, it is evident that DBMS allows user to input
data, share the data, edit the data, manipulate the data, and display the data
in the database.
Q) Explain Structure of DBMS
A) Structure of DBMS:
An overview of the structure of database
management system is shown in Fig. 1.3.
A DBMS is a software package, which translates
data from its logical representation to its physical representation and back.
The DBMS uses an application specific database
description to define this translation. The database description is generated
by a database designer from his or her conceptual view of the database, which
is called the Conceptual Schema. The translation from the conceptual schema to
the database description is performed using a data definition language (DDL) or
a graphical or textual design interface.
Q) What are the Objectives of DBMS? Explain
it.
A) The main objectives of database management system are data availability,
data integrity, data security, and data independence.
1.
Data Availability
Data availability refers to the fact that the
data are made available to wide variety of users in a meaningful format at
reasonable cost so that the users can easily access the data.
2.
Data Integrity
Data integrity refers to the correctness of
the data in the database. In otherwords, the data available in the database is
a reliable data.
3.
Data Security
Data security refers to the fact that only
authorized users can access the data. Data security can be enforced by passwords.
If two separate users are accessing a particular data at the same time, the
DBMS must not allow them to make conflicting changes.
4.
Data Independence
DBMS allows the user to store, update, and
retrieve data in an efficient manner. DBMS provides an “abstract view” of how
the data is stored in the database.
In order to store the information efficiently,
complex data structures are used to represent the data. The system hides
certain details of how the data are stored and maintained.
Q) Explain the Evolution of Database
Management Systems
File-based system was the predecessor to the
database management system.
The chronological order of the development of
DBMS is as follows:
–
Flat files – 1960s–1980s
–
Hierarchical – 1970s–1990s
–
Network – 1970s–1990s
–
Relational – 1980s–present
–
Object-oriented – 1990s–present
–
Object-relational – 1990s–present
–
Data warehousing – 1980s–present
–
Web-enabled – 1990s–present
Early 1960s. Charles Bachman at
GE created the first general purpose DBMS Integrated Data Store. It created the
basis for the network model which was standardized by CODASYL (Conference on
Data System Language).
Late 1960s. IBM developed the
Information Management System (IMS). IMS used an alternate model, called the
Hierarchical Data Model.
1970. Edgar Codd, from IBM created the Relational
Data Model. In 1981 Codd received the Turing Award for his contributions to
database theory. Codd Passed away in April 2003.
1976. Peter Chen presented Entity-Relationship
model, which is widely used in database design.
1980. SQL developed by IBM, became the standard
query language for databases.
SQL was standardized by ISO.
1980s and 1990s. IBM, Oracle,
Informix and others developed powerful DBMS
Q) Briefly explain the Classification of
Database Management System
A) The database management system can be
broadly classified into (1) Passive
Database Management System and (2) Active Database Management System:
- Passive Database Management System. Passive Database Management Systems are program-driven. In passive database management system the users query the current state of database and retrieve the information currently available in the database. Traditional DBMS are passive in the sense that they are explicitly and synchronously invoked by user or application program initiated operations. Applications send requests for operations to be performed by the DBMS and wait for the DBMS to confirm and return any possible answers. The operations can be definitions and updates of the schema, as well as queries and updates of the data.
- Active Database Management System. Active Database Management Systems are data-driven or event-driven systems. In active database management system, the users specify to the DBMS the information they need.
If the information of interest is currently available,
the DBMS actively monitors the arrival of the desired information and provides
it to the relevant users. The scope of a query in a passive DBMS is limited to
the past and present data, whereas the scope of a query in an active DBMS
additionally includes future data. An active DBMS reverses the control flow
between applications and the DBMS instead of only applications calling the
DBMS, the DBMS may also call applications in an active DBMS.
Active databases contain a set of active rules
that consider events that represent database state changes, look for TRUE or
FALSE conditions as the result of a database predicate or query, and take an
action via a data manipulation program embedded in the system. Alert is
extension architecture at the IBM Almaden Research, for experimentation with
active databases.
Q) Write a note on File-Based System.
Prior to DBMS, file system provided by OS was
used to store information.
In a file-based system, we have collection of
application programs that perform services for the end users. Each program
defines and manages its own data.
Consider University database, the University
database contains details about student, faculty, lists of courses offered, and
duration of course, etc. In File-based processing for each database there is
separate application program which is shown in Fig. 1.4.
One group of users may be interested in
knowing the courses offered by the university. One group of users may be
interested in knowing the faculty information. The information is stored in
separate files and separate applications programs are written.
Q) What are the Drawbacks of File-Based System?
Explain it.
The limitations of file-based approach are
duplication of data, data dependence, incompatible file formats, separation,
and isolation of data.
1.
Duplication of Data:
Duplication of data means same data being
stored more than once. This can also be termed as data redundancy. Data
redundancy is a problem in file based approach due to the decentralized
approach. The main drawbacks of duplication of data are:
– Duplication of data leads to wastage of
storage space. If the storage space is wasted it will have a direct impact on
cost. The cost will increase.
– Duplication of data can lead to loss of data
integrity; the data are no longer consistent. Assume that the employee detail
is stored both in the department and in the main office. Now the employee
changes his contact address. The changed address is stored in the department
alone and not in the main office. If some important information has to be sent
to his contact address from the main office then that information will be lost.
This is due to the lack of decentralized
approach.
2.
Data Dependence
Data dependence means the application program
depends on the data. If some modifications have to be made in the data, then
the application program has to be rewritten. If the application program is
independent of the storage structure of the data, then it is termed as data
independence. Data independence is generally preferred as it is more flexible.
But in file-based system there is program-data dependence.
3.
Incompatible File Formats
As file-based system lacks program data
independence, the structure of the file depends on the application programming
language. For example, the structure of the file generated by FORTRAN program
may be different from the structure of a file generated by “C” program. The
incompatibility of such files makes them difficult to process jointly.
4.
Separation and Isolation of Data
In file-based approach, data are isolated in
separate files. Hence it is difficult to access data. The application
programmer must synchronize the processing of two files to ensure that the
correct data are extracted. This difficulty is more if data has to be retrieved
from more than two files.
The draw backs of conventional file-based approach are summarized as:
1. We have to store the information in a
secondary memory such as a disk. If the volume of information is large; it will
occupy more memory space.
2. We have to depend on the addressing facilities
of the system. If the database is very large, then it is difficult to address
the whole set of records.
3. For each query, for example the address of
the student and the list of electives that the student has chosen, we have to
write separate programs.
4. While writing several programs, lot of
variables will be declared and it will occupy some space.
5. It is difficult to ensure the integrity and
consistency of the data when more than one program accesses some file and
changes the data.
6. In case of a system crash, it becomes hard
to bring back the data to a consistent state.
7. “Data redundancy” occurs when identical
data are distributed over various files.
8. Data distributed in various files may be in
different formats hence it is difficult to share data among different
application (Data Isolation).
Advantages of DBMS
There are many advantages of database
management system. Some of the advantages are listed later:
1. Centralized data management.
2. Data Independence.
3. System Integration.
1.
Centralized Data Management
In DBMS all files are integrated into one
system thus reducing redundancies and making data management more efficient.
2.
Data Independence
Data independence means that programs are
isolated from changes in the way the data are structured and stored. In a
database system, the database management system provides the interface between
the application programs and the data. Physical data independence means the
applications need not worry about how the data are physically structured and
stored. Applications should work with a logical data model and declarative
query language.
If major changes were to be made to the data,
the application programs may need to be rewritten. When changes are made to the
data representation, the data maintained by the DBMS is changed but the DBMS
continues to provide data to application programs in the previously used way.
Data independence is the immunity of
application programs to changes in storage structures and access techniques.
For example if we add a new attribute, change index structure then in
traditional file processing system, the applications are affected. But in a
DBMS environment these changes are reflected in the catalog, as a result the
applications are not affected. Data independence can be physical data
independence or logical data independence.
Physical data independence is the ability to
modify physical schema without causing the conceptual schema or application
programs to be rewritten.
Logical data independence is the ability to
modify the conceptual schema without having to change the external schemas or
application programs.
3.
Data Inconsistency
Data inconsistency means different copies of
the same data will have different values. For example, consider a person
working in a branch of an organization.
The details of the person will be stored both
in the branch office as well as in the main office. If that particular person
changes his address, then the “change of address” has to be maintained in the
main as well as the branch office.
For example the “change of address” is
maintained in the branch office but not in the main office, then the data about
that person is inconsistent.
DBMS is designed to have data consistency.
Some of the qualities achieved in DBMS are:
1. Data redundancy −→ Reduced in DBMS.
2. Data independence −→ Activated in DBMS.
3. Data inconsistency −→ Avoided in DBMS.
4. Centralizing the data −→ Achieved in DBMS.
5. Data integrity −→ Necessary for
efficient Transaction.
6. Support for multiple views −→ Necessary for
security reasons.
– Data
redundancy means duplication of data. Data redundancy will occupy more
space hence it is not desirable.
– Data
independence means independence between application program and the data.
The advantage is that when the data representation changes, it is not necessary
to change the application program.
– Data
inconsistency means different copies of the same data will have different
values.
– Centralizing the data means data can be
easily shared between the users but the main concern is data security.
– The main threat to data integrity comes from
several different users attempting to update the same data at the same time.
For example, “The number of booking made is larger than the capacity of the
aircraft/train.”
– Support for multiple views means DBMS allows
different users to see different “views” of the database, according to the
perspective each one requires. This concept is used to enhance the security of
the database.
Q) Explain ANSI/SPARK Data Model (American
National Standard Institute/ Standards Planning and Requirements Committee)
The distinction between the logical and
physical representation of data were recognized in 1978 when ANSI/SPARK
committee proposed a generalized framework for database systems. This framework
provided a three-level architecture, three levels of abstraction at which the
database could be viewed.
1.
Need for Abstraction
The main objective of DBMS is to store and
retrieve information efficiently; all the users should be able to access same
data. The designers use complex data structure to represent the data, so that
data can be efficiently stored and retrieved, but it is not necessary for the
users to know physical database storage details. The developers hide the
complexity from users through several levels of abstraction.
2.
Data Independence
Data independence means the internal structure
of database should be unaffected by changes to physical aspects of storage.
Because of data independence, the Database administrator can change the
database storage structures without affecting the users view.
The different levels of data abstraction are:
1. Physical level
or internal level
3. View level or external level
1.
Physical Level
2.
Logical Level
Logical level describes what data are stored
in the database and what relationships exist among those data. Logical level
describes the entire database in terms of a small number of simple structures.
The implementation of simple structure of the logical level may involve complex
physical level structures; the user of the logical level does not need to be
aware of this complexity. Database administrator use the logical level of
abstraction.
3.
View Level
View level is the highest level of
abstraction. It is the view that the individual user of the database has. There
can be many view level abstractions of the same data. The different levels of
data abstraction are shown in Fig. 1.6.
Q) Explain Database Instances and Schema.
Database Schema:
A schema is also an object in the database. It is explicitly created using the CREATE SCHEMA statement with the current user recorded as the schema owner. It can also be implicitly created when another object is created, provided the user has IMPLICIT SCHEMA authority.
Q) Explain briefly about Data Models.
A) Data model is collection of conceptual
tools for describing data, relationship between data, and consistency
constraints. Data models help in describing the structure of data at the
logical level. Data model describe the structure of the database. A data model
is the set of conceptual constructs available for defining a schema. The data
model is a language for describing the data and database, it may consist of
abstract concepts, which must be translated by the designer into the constructs
of the data definition interface, or it may consist of constructs, which are
directly supported by the data definition interface. The constructs of the data
model may be defined at many levels of abstraction.
The entire structure of a database can be described using a data
model. It is a collection of conceptual tools for describing data, data
relationships, data semantics, and consistency constraints.
Data models can be classified into following types.
1.
Object Based Logical Models.
2.
Record Based Logical Models.
3.
Physical Models.
1.Object Based Logical Models: These
models can be used in describing the data at the logical and view levels. These
models are classified into following types.
a.
The entity-relationship model.
b.
The object-oriented model.
c.
The semantic data model.
d.
The functional data model.
THE ENTITY-RELATIONSHIP MODEL:
·
The
entity-relationship (E-R) data model is a collection of basic objects, called
entities, and of relationships among these objects.
·
An entity
is a “thing” or “object” in the real world that is distinguishable from other
objects. For example, each person is an entity, and bank accounts can be
considered as entities.
·
A
relationship is an association among several entities. For example, a depositor
relationship associates a customer with each account that she has.
The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram, which is built up from the following components:
• Rectangles, which represent entity sets
• Ellipses, which represent attributes
• Diamonds, which represent relationships
among entity sets
• Lines, which link attributes to entity
sets and entity sets to relationships
2.Record
Based Logical Models: These
models can also be used in describing the data at the logical and view levels.
These models can be classified into,
a. Relational model.
b. Network model.
c. Hierarchal model.
a. Relational Model:
·
The
relational model uses a collection of tables to represent both data and the
relationships among those data.
·
Each
table has multiple columns, and each column has a unique name. Figure presents
a sample relational database comprising three tables:
·
It shows
how tables are linked, what type of links are between
tables, what keys are used, what information is referenced between tables. It's
an essential part of developing a normalised database
structure to prevent repeat and redundant data storage
 |
 |
 |
One shows details of bank customers, the second
shows accounts, and the third shows which accounts belong to which customers.
b.
Network Model: It is a
modified version of hierarchical database. In network database structure each
node may have several parents.
» It is very difficult to develop this type of database structures.
» It is useful for one-to-one and one-to-many record relationships.
» The relationships should be pre-determined. The records in the
database are organized as a collection of arbitrary graph.
c. Hierarchical Model: - In this database structure,
records are logically organised into a hierarchy of relationships and involve
an inverted tree like structure. The
tree consists of hierarchy of nodes and the uppermost tree is called parent. Every element can have any number of
lower level elements, called children, but every node will have only one
parent..
3. Physical Models: These models can be used in
describing the data at the lowest level, i.e. physical level. These models can
be classified into
a. Unifying model
b. Frame
memory model
Q) Explain the Components and
Interfaces of Database Management System.
A database management system involves five major components: data, hardware, software, procedure, and
users. These components and the interface between the components are shown
in Fig. 1.7.
1.
Hardware
The hardware can range from a single personal
computer, to a single mainframe, to a network of computers. The particular
hardware depends on the requirements of the organization and the DBMS used.
Some DBMSs run only on particular operating systems, while others run on a wide
variety of operating systems. A DBMS requires a minimum amount of main memory
and disk space to run, but this minimum configuration may not necessarily give acceptable
performance.
2.
Software
The software includes the DBMS software,
application programs together with the operating systems including the network
software if the DBMS is being used over a network. The application programs are
written in third-generation programming languages like “C,” COBOL, FORTRAN,
Ada, Pascal, etc. or using fourth-generation language such as SQL, embedded in
a third-generation language. The target DBMS may have its own fourth-generation
tools which allow development of applications through the provision of
nonprocedural query languages, report generators, graphics generators, and
application generators.
The use of fourth-generation tools can improve
productivity significantly and produce programs that are easier to maintain.
3.
Data
A database is a repository for data which, in
general, is both integrated and shared. Integration means that the database may
be thought of as a unification of several otherwise distinct files, with any
redundancy among those files partially or wholly eliminated. The sharing of a
database refers to the sharing of data by different users, in the sense that
each of those users may have access to the same piece of data and may use it
for different purposes.
Any given user will normally be concerned with
only a subset of the whole database. The main features of the data in the
database are listed later:
1. The data in the database is well organized
(structured)
2. The data in the database is related
3. The data are accessible in different orders
without great difficulty
4.
Procedure
Procedures are the rules that govern the
design and the use of database. The procedure may contain information on how to
log on to the DBMS, start and stop the DBMS, procedure on how to identify the
failed component, how to recover the database, change the structure of the
table, and improve the performance.
5.
People Interacting with Database
Here people refers to the people who manages
the database, database administrator, people who design the application
program, database designer and the people who interacts with the database,
database users.
A DBMS is typically run as a back-end server
in a local or global network, offering services to clients directly or to
Application Servers
Q) Who is DBA. What are the responsibilities
of DBA?
DBA-Database Administrator:
Database Administrator is a person having
central control over data and programs accessing that data. The database
administrator is a manager whose responsibilities are focused on management of
technical aspects of the database system. The objectives of database
administrator are given as follows:
1. To control the database environment
2. To standardize
the use of database and associated software
3. To support the development and maintenance
of database application projects
4. To ensure all documentation related to
standards and implementation is up-to-date
The summarized objectives of database
administrator are shown in Fig. 1.8.
Responsibilities of Database Administrator
(DBA)
The responsibility of the database
administrator is to maintain the integrity, security, and availability of data.
A database must be protected from database and from hardware or software
failures that corrupt data. Protection from accidents that cause data
inaccuracy is a part of maintaining data integrity.
Protecting the database from unauthorized or
malicious use is termed as database security. The responsibilities of the
database administrator are summarized as follows:
1. Authorizing access to the database.
2. Coordinating and monitoring its use.
3. Acquiring hardware and software resources
as needed.
4. Backup and recovery. DBA has to ensure
regular backup of database, incase of damage, suitable recovery procedure are
used to bring the database up with little downtime as possible
Q) Explain briefly about different types of Database Users
Database users are the people who need
information from the database to carry out their business responsibility. The
database users can be broadly classified into two categories like application
programmers and end users.
1.
Sophisticated End Users
Sophisticated end users interact with the
system without writing programs. They form requests by writing queries in a
database query language. These are submitted to query processor. Analysts who
submit queries to explore data in the database fall in this category.
2.
Specialized End Users
Specialized end users write specialized
database application that does not fit into data-processing frame work.
Application involves knowledge base and expert system, environment modeling
system, etc.
3.
Naive End Users
Naıve end user interact with the system by
using permanent application program Example: Query made by the student, namely
number of books borrowed in library database.
4.
System Analysts
System analysts determine the requirements of
end user, and develop specification for canned transaction that meets this
requirement
Q) Explain Database Architecture
Database architecture essentially describes
the location of all the pieces of information that make up the database
application. The database architecture can be broadly classified into two-,
three-, and multitier architecture.
1.
Two-Tier
Architecture
Two-Tier
Architecture
The two-tier architecture is a client–server
architecture in which the client contains the presentation code and the SQL
statements for data access. The database server processes the SQL statements
and sends query results back to the client. The two-tier architecture is shown
in Fig. 1.9. Two-tier client/server provides a basic separation of tasks. The
client, or first tier, is primarily responsible for the presentation of data to the user
and the “server,” or second tier, is primarily responsible for supplying data services to the client
Presentation Services: “Presentation
services” refers to the portion of the application which presents data to the
user. In addition, it also provides for the mechanisms in which the user will
interact with the data. More simply put, presentation logic defines and
interacts with the user interface. The presentation of the data should generally
not contain any validation rules.
Business Services/objects
“Business services” are a category of
application services. Business services encapsulate an organizations business
processes and requirements. These rules are derived from the steps necessary to
carry out day-today business in an organization. These rules can be validation
rules, used to be sure that the incoming information is of a valid type and
format, or they can be process
rules, which ensure that the proper business
process is followed in order to complete an operation.
Application Services
“Application services” provide other functions
necessary for the application.
Data Services
“Data services” provide access to data
independent of their location. The data can come from legacy mainframe, SQL
RDBMS, or proprietary data access systems. Once again, the data services
provide a standard interface for accessing data
Three-tier Architecture
A “Multitier,”
often referred to as “three-tier” or “N-tier,” architecture provides greater
application scalability, lower maintenance, and increased reuse of components.
Three-tier architecture offers a technology neutral method of building
client/server applications with vendors who employ standard interfaces which
provide services for each logical “tier.” The three-tier architecture is shown
in Fig. 1.10.
From this figure, it is clear that in order to improve the performance a
second-tier is included between the client and the server. Through standard
tiered interfaces, services are made available to the application.
A single application can employ many different
services which may reside on dissimilar platforms or are developed and
maintained with different tools. This approach allows a developer to leverage investments
in existing systems while creating new application which can utilize existing
resources. Although the three-tier architecture addresses performance
degradations of the two-tier architecture, it does not address
division-of-processing concerns. The PC clients and the database server still
contain the same division of code although the tasks of the database server are
reduced. Multiple-tier architectures provide more flexibility on division of
processing.
Q) Explain the Situations where DBMS is not
Necessary
It is also necessary to specify situations
where it is not necessary to use a DBMS. If traditional file processing system
is working well, and if it takes more money and time to design a database, it
is better not to go for the DBMS. Moreover if only one person maintains the
data and that person is not skilled in designing a database as well as not
comfortable in using the DBMS then it is not advisable to go for DBMS.
DBMS is undesirable under following
situations:
– DBMS is undesirable if the application is
simple, well-defined, and not expected to change.
– Runtime overheads are not feasible because
of real-time requirements.
– Multiple accesses to data are not required.
Compared with file systems, databases have
some disadvantages:
1. High cost of DBMS this includes:
– Higher hardware costs
– Higher programming costs
– High conversion costs
2. Slower processing of some applications
3. Increased vulnerability
4. More difficult recovery
Q) List out the DBMS Vendors and their
Products
Some of the popular DBMS vendors and their
corresponding products are given Table 1.1.
Review Questions
1.1. What are the drawbacks of file processing
system?
The drawbacks of file processing system are:
– Duplication of data, which leads to wastage
of storage space and data inconsistency.
– Separation and isolation of data, because of
which data cannot be used together.
– No program data independence.
1.2. What is meant by Metadata?
Metadata are data about data but not the
actual data
1.3. Define the term data dictionary?
Data dictionary is a file that contains
Metadata.
1.4. What are the responsibilities of database
administrator?
1.5. Mention three situations where it is not
desirable to use DBMS?
The situations where it is not desirable to
use DBMS are:
– The database and applications are not
expected to change.
– Data are not accessed by multiple users.
1.6. What is meant by data independence?
Data independence renders application programs
(e.g., SQL scripts) immune to changes in the logical and physical organization
of data in the system.
Logical organization refers to changes
in the Schema. Example adding a column or tuples does not stop queries from
working.
Physical organization refers to changes
in indices, file organizations, etc.
1.7. What is meant by Physical and Logical data
independence?
In logical data independence, the conceptual
schema can be changed without changing the external schema. In physical data
independence, the internal schema can be changed without changing the
conceptual schema.
1.8. What are some disadvantages of using a DBMS
over flat file system?
– DBMS initially costs more than flat file
system
– DBMS requires skilled staff
1.9. What are the steps to design a good database?
– First find out the requirements of the user
– Design a view for each important application
– Integrate the views giving the conceptual
schema, which is the union of all views
– Map to the data model provided by the DBMS
(usually relational)
– Design external views
– Choose physical structures (indexes, etc.)
1.10. What is Database? Give an example.
A Database is a collection of related data.
Here, the term “data” means that known facts that can be record. Examples of
database are library information system, bus, railway, and airline reservation
system, etc.
1.11. Define – DBMS.
DBMS is a collection of programs that enables
users to create and maintain a database.
1.12. Mention various types of databases?
The different types of databases are:
– Multimedia database
– Spatial database (Geographical Information System
Database)
– Real-time or Active Database
– Data Warehouse or On-line Analytical
Processing Database
1.13. Mention the advantages of using DBMS?
The advantages of using DBMS are:
– Controlling Redundancy
– Enforcing Integrity Constraints so as to
maintain the consistency of the database
– Providing Backup and recovery facilities
– Restricting unauthorized access
– Providing multiple user interfaces
– Providing persistent storage of program
objects and datastructures
1.14. What is “Snapshot” or “Database State”?
The data in the database at a particular
moment is known as “Database
State” or “Snapshot” of the Database
1.15. Define Data Model.
It is a collection of concepts that can be
used to describe the structure of a database.
The datamodel provides necessary means to
achieve the abstraction i.e., hiding the details of data storage.
1.16. Mention the various categories of Data Model.
The various categories of datamodel are:
– High Level or Conceptual Data Model
(Example: ER model)
– Low Level or Physical Data Model
– Representational or Implementational Data
Model
– Relational Data Model
– Network and Hierarchal Data Model
– Record-based Data Model
– Object-based Data Model
Define the concept of “database schema.”
Describe the types of schemas that exist in a database complying with the three
levels ANSI/SPARC architecture.
Database schema is nothing but description of
the database. The types of schemas that exist in a database complying with
three levels of ANSI/SPARC architecture are:
– External schema
– Conceptual schema
– Internal schema
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