DBMS - QUICK GUIDE
http://www.tutorialspoint.com/dbms/dbms_quick_guide.htm Copyright © tutorialspoint.com
DBMS - OVERVIEW
Database is a collection of related data and data is a collection of facts and figures that can be
processed to produce information.
Mostly data represents recordable facts. Data aids in producing information, which is based on
facts. For example, if we have data about marks obtained by all students, we can then conclude
about toppers and average marks.
A database management system stores data in such a way that it becomes easier to retrieve,
manipulate, and produce information.
Characteristics
Traditionally, data was organized in file formats. DBMS was a new concept then, and all the
research was done to make it overcome the deficiencies in traditional style of data management.
A modern DBMS has the following characteristics −
Real-world entity − A modern DBMS is more realistic and uses real-world entities to design
its architecture. It uses the behavior and attributes too. For example, a school database may
use students as an entity and their age as an attribute.
Relation-based tables − DBMS allows entities and relations among them to form tables. A
user can understand the architecture of a database just by looking at the table names.
Isolation of data and application − A database system is entirely different than its data. A
database is an active entity, whereas data is said to be passive, on which the database works
and organizes. DBMS also stores metadata, which is data about data, to ease its own process.
Less redundancy − DBMS follows the rules of normalization, which splits a relation when
any of its attributes is having redundancy in values. Normalization is a mathematically rich
and scientific process that reduces data redundancy.
Consistency − Consistency is a state where every relation in a database remains consistent.
There exist methods and techniques, which can detect attempt of leaving database in
inconsistent state. A DBMS can provide greater consistency as compared to earlier forms of
data storing applications like file-processing systems.
Query Language − DBMS is equipped with query language, which makes it more efficient to
retrieve and manipulate data. A user can apply as many and as different filtering options as
required to retrieve a set of data. Traditionally it was not possible where file-processing
system was used.
ACID Properties − DBMS follows the concepts of Atomicity, Consistency, Isolation, and
Durability normallyshortenedasACID. These concepts are applied on transactions, which
manipulate data in a database. ACID properties help the database stay healthy in multi-
transactional environments and in case of failure.
Multiuser and Concurrent Access − DBMS supports multi-user environment and allows
them to access and manipulate data in parallel. Though there are restrictions on
transactions when users attempt to handle the same data item, but users are always
unaware of them.
Multiple views − DBMS offers multiple views for different users. A user who is in the Sales
department will have a different view of database than a person working in the Production
department. This feature enables the users to have a concentrate view of the database
according to their requirements.
Security − Features like multiple views offer security to some extent where users are unable
to access data of other users and departments. DBMS offers methods to impose constraints
while entering data into the database and retrieving the same at a later stage. DBMS offers
, many different levels of security features, which enables multiple users to have different
views with different features. For example, a user in the Sales department cannot see the
data that belongs to the Purchase department. Additionally, it can also be managed how
much data of the Sales department should be displayed to the user. Since a DBMS is not
saved on the disk as traditional file systems, it is very hard for miscreants to break the code.
Users
A typical DBMS has users with different rights and permissions who use it for different purposes.
Some users retrieve data and some back it up. The users of a DBMS can be broadly categorized as
follows −
Administrators − Administrators maintain the DBMS and are responsible for administrating
the database. They are responsible to look after its usage and by whom it should be used.
They create access profiles for users and apply limitations to maintain isolation and force
security. Administrators also look after DBMS resources like system license, required tools,
and other software and hardware related maintenance.
Designers − Designers are the group of people who actually work on the designing part of
the database. They keep a close watch on what data should be kept and in what format. They
identify and design the whole set of entities, relations, constraints, and views.
End Users − End users are those who actually reap the benefits of having a DBMS. End
users can range from simple viewers who pay attention to the logs or market rates to
sophisticated users such as business analysts.
DBMS - ARCHITECTURE
The design of a DBMS depends on its architecture. It can be centralized or decentralized or
hierarchical. The architecture of a DBMS can be seen as either single tier or multi-tier. An n-tier
architecture divides the whole system into related but independent n modules, which can be
independently modified, altered, changed, or replaced.
In 1-tier architecture, the DBMS is the only entity where the user directly sits on the DBMS and uses
it. Any changes done here will directly be done on the DBMS itself. It does not provide handy tools
for end-users. Database designers and programmers normally prefer to use single-tier
architecture.
If the architecture of DBMS is 2-tier, then it must have an application through which the DBMS can
be accessed. Programmers use 2-tier architecture where they access the DBMS by means of an
application. Here the application tier is entirely independent of the database in terms of operation,
design, and programming.
3-tier Architecture
A 3-tier architecture separates its tiers from each other based on the complexity of the users and
how they use the data present in the database. It is the most widely used architecture to design a
DBMS.
, Database Data Tier − At this tier, the database resides along with its query processing
languages. We also have the relations that define the data and their constraints at this level.
Application Middle Tier − At this tier reside the application server and the programs that
access the database. For a user, this application tier presents an abstracted view of the
database. End-users are unaware of any existence of the database beyond the application.
At the other end, the database tier is not aware of any other user beyond the application tier.
Hence, the application layer sits in the middle and acts as a mediator between the end-user
and the database.
User Presentation Tier − End-users operate on this tier and they know nothing about any
existence of the database beyond this layer. At this layer, multiple views of the database can
be provided by the application. All views are generated by applications that reside in the
application tier.
Multiple-tier database architecture is highly modifiable, as almost all its components are
independent and can be changed independently.
DBMS - DATA MODELS
Data models define how the logical structure of a database is modeled. Data Models are
fundamental entities to introduce abstraction in a DBMS. Data models define how data is
connected to each other and how they are processed and stored inside the system.
The very first data model could be flat data-models, where all the data used are to be kept in the
same plane. Earlier data models were not so scientific, hence they were prone to introduce lots of
duplication and update anomalies.
Entity-Relationship Model
Entity-Relationship ER Model is based on the notion of real-world entities and relationships among
them. While formulating real-world scenario into the database model, the ER Model creates entity
set, relationship set, general attributes and constraints.
ER Model is best used for the conceptual design of a database.
ER Model is based on −
Entities and their attributes.
, Relationships among entities.
These concepts are explained below.
Entity − An entity in an ER Model is a real-world entity having properties called attributes.
Every attribute is defined by its set of values called domain. For example, in a school
database, a student is considered as an entity. Student has various attributes like name, age,
class, etc.
Relationship − The logical association among entities is called relationship. Relationships
are mapped with entities in various ways. Mapping cardinalities define the number of
association between two entities.
Mapping cardinalities −
one to one
one to many
many to one
many to many
Relational Model
The most popular data model in DBMS is the Relational Model. It is more scientific a model than
others. This model is based on first-order predicate logic and defines a table as an n-ary relation.
The main highlights of this model are −
Data is stored in tables called relations.
Relations can be normalized.
http://www.tutorialspoint.com/dbms/dbms_quick_guide.htm Copyright © tutorialspoint.com
DBMS - OVERVIEW
Database is a collection of related data and data is a collection of facts and figures that can be
processed to produce information.
Mostly data represents recordable facts. Data aids in producing information, which is based on
facts. For example, if we have data about marks obtained by all students, we can then conclude
about toppers and average marks.
A database management system stores data in such a way that it becomes easier to retrieve,
manipulate, and produce information.
Characteristics
Traditionally, data was organized in file formats. DBMS was a new concept then, and all the
research was done to make it overcome the deficiencies in traditional style of data management.
A modern DBMS has the following characteristics −
Real-world entity − A modern DBMS is more realistic and uses real-world entities to design
its architecture. It uses the behavior and attributes too. For example, a school database may
use students as an entity and their age as an attribute.
Relation-based tables − DBMS allows entities and relations among them to form tables. A
user can understand the architecture of a database just by looking at the table names.
Isolation of data and application − A database system is entirely different than its data. A
database is an active entity, whereas data is said to be passive, on which the database works
and organizes. DBMS also stores metadata, which is data about data, to ease its own process.
Less redundancy − DBMS follows the rules of normalization, which splits a relation when
any of its attributes is having redundancy in values. Normalization is a mathematically rich
and scientific process that reduces data redundancy.
Consistency − Consistency is a state where every relation in a database remains consistent.
There exist methods and techniques, which can detect attempt of leaving database in
inconsistent state. A DBMS can provide greater consistency as compared to earlier forms of
data storing applications like file-processing systems.
Query Language − DBMS is equipped with query language, which makes it more efficient to
retrieve and manipulate data. A user can apply as many and as different filtering options as
required to retrieve a set of data. Traditionally it was not possible where file-processing
system was used.
ACID Properties − DBMS follows the concepts of Atomicity, Consistency, Isolation, and
Durability normallyshortenedasACID. These concepts are applied on transactions, which
manipulate data in a database. ACID properties help the database stay healthy in multi-
transactional environments and in case of failure.
Multiuser and Concurrent Access − DBMS supports multi-user environment and allows
them to access and manipulate data in parallel. Though there are restrictions on
transactions when users attempt to handle the same data item, but users are always
unaware of them.
Multiple views − DBMS offers multiple views for different users. A user who is in the Sales
department will have a different view of database than a person working in the Production
department. This feature enables the users to have a concentrate view of the database
according to their requirements.
Security − Features like multiple views offer security to some extent where users are unable
to access data of other users and departments. DBMS offers methods to impose constraints
while entering data into the database and retrieving the same at a later stage. DBMS offers
, many different levels of security features, which enables multiple users to have different
views with different features. For example, a user in the Sales department cannot see the
data that belongs to the Purchase department. Additionally, it can also be managed how
much data of the Sales department should be displayed to the user. Since a DBMS is not
saved on the disk as traditional file systems, it is very hard for miscreants to break the code.
Users
A typical DBMS has users with different rights and permissions who use it for different purposes.
Some users retrieve data and some back it up. The users of a DBMS can be broadly categorized as
follows −
Administrators − Administrators maintain the DBMS and are responsible for administrating
the database. They are responsible to look after its usage and by whom it should be used.
They create access profiles for users and apply limitations to maintain isolation and force
security. Administrators also look after DBMS resources like system license, required tools,
and other software and hardware related maintenance.
Designers − Designers are the group of people who actually work on the designing part of
the database. They keep a close watch on what data should be kept and in what format. They
identify and design the whole set of entities, relations, constraints, and views.
End Users − End users are those who actually reap the benefits of having a DBMS. End
users can range from simple viewers who pay attention to the logs or market rates to
sophisticated users such as business analysts.
DBMS - ARCHITECTURE
The design of a DBMS depends on its architecture. It can be centralized or decentralized or
hierarchical. The architecture of a DBMS can be seen as either single tier or multi-tier. An n-tier
architecture divides the whole system into related but independent n modules, which can be
independently modified, altered, changed, or replaced.
In 1-tier architecture, the DBMS is the only entity where the user directly sits on the DBMS and uses
it. Any changes done here will directly be done on the DBMS itself. It does not provide handy tools
for end-users. Database designers and programmers normally prefer to use single-tier
architecture.
If the architecture of DBMS is 2-tier, then it must have an application through which the DBMS can
be accessed. Programmers use 2-tier architecture where they access the DBMS by means of an
application. Here the application tier is entirely independent of the database in terms of operation,
design, and programming.
3-tier Architecture
A 3-tier architecture separates its tiers from each other based on the complexity of the users and
how they use the data present in the database. It is the most widely used architecture to design a
DBMS.
, Database Data Tier − At this tier, the database resides along with its query processing
languages. We also have the relations that define the data and their constraints at this level.
Application Middle Tier − At this tier reside the application server and the programs that
access the database. For a user, this application tier presents an abstracted view of the
database. End-users are unaware of any existence of the database beyond the application.
At the other end, the database tier is not aware of any other user beyond the application tier.
Hence, the application layer sits in the middle and acts as a mediator between the end-user
and the database.
User Presentation Tier − End-users operate on this tier and they know nothing about any
existence of the database beyond this layer. At this layer, multiple views of the database can
be provided by the application. All views are generated by applications that reside in the
application tier.
Multiple-tier database architecture is highly modifiable, as almost all its components are
independent and can be changed independently.
DBMS - DATA MODELS
Data models define how the logical structure of a database is modeled. Data Models are
fundamental entities to introduce abstraction in a DBMS. Data models define how data is
connected to each other and how they are processed and stored inside the system.
The very first data model could be flat data-models, where all the data used are to be kept in the
same plane. Earlier data models were not so scientific, hence they were prone to introduce lots of
duplication and update anomalies.
Entity-Relationship Model
Entity-Relationship ER Model is based on the notion of real-world entities and relationships among
them. While formulating real-world scenario into the database model, the ER Model creates entity
set, relationship set, general attributes and constraints.
ER Model is best used for the conceptual design of a database.
ER Model is based on −
Entities and their attributes.
, Relationships among entities.
These concepts are explained below.
Entity − An entity in an ER Model is a real-world entity having properties called attributes.
Every attribute is defined by its set of values called domain. For example, in a school
database, a student is considered as an entity. Student has various attributes like name, age,
class, etc.
Relationship − The logical association among entities is called relationship. Relationships
are mapped with entities in various ways. Mapping cardinalities define the number of
association between two entities.
Mapping cardinalities −
one to one
one to many
many to one
many to many
Relational Model
The most popular data model in DBMS is the Relational Model. It is more scientific a model than
others. This model is based on first-order predicate logic and defines a table as an n-ary relation.
The main highlights of this model are −
Data is stored in tables called relations.
Relations can be normalized.
