Ans: 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).
Q) Explain DBMS Approach and its advantages.
DBMS is software that
provides a set of primitives for defining, accessing, and manipulating data. In
DBMS approach, the same data are being shared by different application
programs; as a result data redundancy is minimized. The DBMS approach of data
access is shown in Fig. 1.5.
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
2. Logical level or conceptual level
3. View level or external level
1. Physical Level
It is concerned with the physical storage of the information. It
provides the internal view of the actual physical storage of data. The physical
level describes complex low-level data structures in detail.
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 Instances:
Database change over time as information is inserted and deleted. The
collection of information stored in the database at a particular moment is
called an instance of the database.
Database Schema:
The overall design of the database is called the database schema. A
schema is a collection of named objects. Schemas provide a logical
classification of objects in the database. A schema can contain tables, views,
triggers, functions, packages, and other objects.
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
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
