Database Schema
A database schema is the skeleton structure that represents the logical view of the
entire database. It defines how the data is organized and how the relations among
them are associated. It formulates all the constraints that are to be applied on the
data.
A database schema defines its entities and the relationship among them. It contains
a descriptive detail of the database, which can be depicted by means of schema
diagrams. It’s the database designers who design the schema to help programmers
understand the database and make it useful.
A database schema can be divided broadly into two categories −
Physical Database Schema − This schema pertains to the actual storage of
data and its form of storage like files, indices, etc. It defines how the data will
be stored in a secondary storage.
Logical Database Schema − This schema defines all the logical constraints
that need to be applied on the data stored. It defines tables, views, and
integrity constraints.
Database Instance
It is important that we distinguish these two terms individually. Database schema is
the skeleton of database. It is designed when the database doesn't exist at all. Once
the database is operational, it is very difficult to make any changes to it. A database
schema does not contain any data or information.
A database instance is a state of operational database with data at any given time. It
contains a snapshot of the database. Database instances tend to change with time.
A DBMS ensures that its every instance (state) is in a valid state, by diligently
following all the validations, constraints, and conditions that the database designers
have imposed.
Components –
Hardware
The hardware is the actual computer system used for keeping and accessing the
database. The conventional DBMS hardware consists of secondary storage devices
such as hard disks. Databases run on the range of machines from micro computers
to mainframes.
Software
Software is the actual DBMS between the physical database and the users of the
system. All the requests from the user for accessing the database are handled by
DBMS.
Data
, It is an important component of the database management system. The main task of
DBMS is to process the data. Databases are used to store the data, retrieved, and
updated to and from the databases.
Users
There are a number of users who can access or retrieve the data on demand using
the application and the interfaces provided by the DBMS.
1. Database Administrator (DBA) : Database Administrator (DBA) is a
person/team who defines the schema and also controls the 3 levels of
database. The DBA will then create a new account id and password for
the user if he/she need to access the database. DBA is also responsible
for providing security to the database and he allows only the authorized
users to access/modify the data base. DBA is responsible for the
problems such as security breaches and poor system response time.
DBA also monitors the recovery and backup and provide technical
support.
The DBA has a DBA account in the DBMS which called a system or
superuser account.
DBA repairs damage caused due to hardware and/or software failures.
DBA is the one having privileges to perform DCL (Data Control
Language) operations such as GRANT and REVOKE, to allow/restrict
a particular user from accessing the database.
2. Naive / Parametric End Users : Parametric End Users are the
unsophisticated who don’t have any DBMS knowledge but they frequently
use the database applications in their daily life to get the desired results.
For examples, Railway’s ticket booking users are naive users. Clerks in
any bank is a naive user because they don’t have any DBMS knowledge
but they still use the database and perform their given task.
3. System Analyst :
System Analyst is a user who analyzes the requirements of parametric
end users. They check whether all the requirements of end users are
satisfied.
4. Sophisticated Users : Sophisticated users can be engineers, scientists,
business analyst, who are familiar with the database. They can develop
their own database applications according to their requirement. They
don’t write the program code but they interact the database by writing
SQL queries directly through the query processor.
5. Database Designers : Data Base Designers are the users who design
the structure of database which includes tables, indexes, views, triggers,
stored procedures and constraints which are usually enforced before the
database is created or populated with data. He/she controls what data
must be stored and how the data items to be related. It is responsibility of
Database Designers to understand the requirements of different user
groups and then create a design which satisfies the need of all the user
groups.
A database schema is the skeleton structure that represents the logical view of the
entire database. It defines how the data is organized and how the relations among
them are associated. It formulates all the constraints that are to be applied on the
data.
A database schema defines its entities and the relationship among them. It contains
a descriptive detail of the database, which can be depicted by means of schema
diagrams. It’s the database designers who design the schema to help programmers
understand the database and make it useful.
A database schema can be divided broadly into two categories −
Physical Database Schema − This schema pertains to the actual storage of
data and its form of storage like files, indices, etc. It defines how the data will
be stored in a secondary storage.
Logical Database Schema − This schema defines all the logical constraints
that need to be applied on the data stored. It defines tables, views, and
integrity constraints.
Database Instance
It is important that we distinguish these two terms individually. Database schema is
the skeleton of database. It is designed when the database doesn't exist at all. Once
the database is operational, it is very difficult to make any changes to it. A database
schema does not contain any data or information.
A database instance is a state of operational database with data at any given time. It
contains a snapshot of the database. Database instances tend to change with time.
A DBMS ensures that its every instance (state) is in a valid state, by diligently
following all the validations, constraints, and conditions that the database designers
have imposed.
Components –
Hardware
The hardware is the actual computer system used for keeping and accessing the
database. The conventional DBMS hardware consists of secondary storage devices
such as hard disks. Databases run on the range of machines from micro computers
to mainframes.
Software
Software is the actual DBMS between the physical database and the users of the
system. All the requests from the user for accessing the database are handled by
DBMS.
Data
, It is an important component of the database management system. The main task of
DBMS is to process the data. Databases are used to store the data, retrieved, and
updated to and from the databases.
Users
There are a number of users who can access or retrieve the data on demand using
the application and the interfaces provided by the DBMS.
1. Database Administrator (DBA) : Database Administrator (DBA) is a
person/team who defines the schema and also controls the 3 levels of
database. The DBA will then create a new account id and password for
the user if he/she need to access the database. DBA is also responsible
for providing security to the database and he allows only the authorized
users to access/modify the data base. DBA is responsible for the
problems such as security breaches and poor system response time.
DBA also monitors the recovery and backup and provide technical
support.
The DBA has a DBA account in the DBMS which called a system or
superuser account.
DBA repairs damage caused due to hardware and/or software failures.
DBA is the one having privileges to perform DCL (Data Control
Language) operations such as GRANT and REVOKE, to allow/restrict
a particular user from accessing the database.
2. Naive / Parametric End Users : Parametric End Users are the
unsophisticated who don’t have any DBMS knowledge but they frequently
use the database applications in their daily life to get the desired results.
For examples, Railway’s ticket booking users are naive users. Clerks in
any bank is a naive user because they don’t have any DBMS knowledge
but they still use the database and perform their given task.
3. System Analyst :
System Analyst is a user who analyzes the requirements of parametric
end users. They check whether all the requirements of end users are
satisfied.
4. Sophisticated Users : Sophisticated users can be engineers, scientists,
business analyst, who are familiar with the database. They can develop
their own database applications according to their requirement. They
don’t write the program code but they interact the database by writing
SQL queries directly through the query processor.
5. Database Designers : Data Base Designers are the users who design
the structure of database which includes tables, indexes, views, triggers,
stored procedures and constraints which are usually enforced before the
database is created or populated with data. He/she controls what data
must be stored and how the data items to be related. It is responsibility of
Database Designers to understand the requirements of different user
groups and then create a design which satisfies the need of all the user
groups.
