Advantages and Disadvantages of Database Management System (DBMS):
Advantages of Database Management System:
The DBMS has a number of advantages as compared to traditional computer file
processing approach. The DBA must keep in mind these benefits or capabilities
during designing databases, coordinating and monitoring the DBMS.
The major advantages of DBMS are described below.
1. Controlling Data Redundancy:
In non-database systems (traditional computer file processing), each application
program has its own files. In this case, the duplicated copies of the same data
are created at many places. In DBMS, all the data of an organization is
integrated into a single database. The data is recorded at only one place in the
database and it is not duplicated. For example, the dean's faculty file and the
faculty payroll file contain several items that are identical. When they are
converted into database, the data is integrated into a single database so that
multiple copies of the same data are reduced to-single copy.
In DBMS, the data redundancy can be controlled or reduced but is not removed
completely. Sometimes, it is necessary to create duplicate copies of the same
data items in order to relate tables with each other.
By controlling the data redundancy, you can save
storage space. Similarly, it is useful for retrieving data from database using
queries.
2. Data Consistency:
By controlling the data redundancy, the data consistency is obtained. If a data
item appears only once, any update to its value has to be performed only once
and the updated value (new value of item) is immediately available to all users.
If the DBMS has reduced redundancy to a minimum level, the database system
enforces consistency. It means that when a data item appears more than once in
the database and is updated, the DBMS automatically updates each occurrence of a
data item in the database.
3. Data Sharing:
In DBMS, data can be shared by authorized users of the organization. The DBA
manages the data and gives rights to users to access the data. Many users can be
authorized to access the same set of information simultaneously. The remote
users can also share same data. Similarly, the data of same database can be
shared between different application programs.
4. Data Integration:
In DBMS, data in database is stored in tables. A single database contains
multiple tables and relationships can be created between tables (or associated
data entities). This makes easy to retrieve and update data.
5. Integrity Constraints:
Integrity constraints or consistency rules can be applied to database so that
the correct data can be entered into database. The constraints may be applied to
data item within a single record or they may be applied to relationships between
records.
Examples:
The examples of integrity constraints are:
(i) 'Issue Date' in a library system cannot be later than the corresponding
'Return Date' of a book.
(ii) Maximum obtained marks in a subject cannot exceed 100.
(iii) Registration number of BCS and MCS students must start with 'BCS' and
'MCS' respectively etc.
There are also some standard constraints that are
intrinsic in most of the DBMSs. These are;
| Constraint Name |
Description |
| PRIMARY KEY |
Designates a column or combination of columns as Primary Key and therefore,
values of columns cannot be repeated or left blank. |
| FOREIGN KEY |
Relates one table with another table.
|
| UNIQUE |
Specifies that values of a column or combination of columns cannot be repeated. |
| NOT NULL |
Specifies that a column cannot contain empty values. |
| CHECK |
Specifies a condition which each row of a table must satisfy. |
Most of the DBMSs provide the facility for applying the integrity constraints.
The database designer (or DBA) identifies integrity constraints during database
design. The application programmer can also identify integrity constraints in
the program code during developing the application program. The integrity
constraints are automatically checked at the time of data entry or when the
record is updated. If the data entry operator (end-user) violates an integrity
constraint, the data is not inserted or updated into the database and a message
is displayed by the system. For example, when you draw amount from the bank
through ATM card, then your account balance is compared with the amount you are
drawing. If the amount in your account balance is less than the amount you want
to draw, then a message is displayed on the screen to inform you about your
account balance.
6. Data Security:
Data security is the protection of the database from unauthorized users. Only
the authorized persons are allowed to access the database. Some of the users may
be allowed to access only a part of database i.e., the data that is related to
them or related to their department. Mostly, the DBA or head of a department can
access all the data in the database. Some users may be permitted only to retrieve data, whereas others are allowed to retrieve as well as to update data. The
database access is controlled by the DBA. He creates the accounts of users and
gives rights to access the database. Typically, users or group of users are
given usernames protected by passwords.
Most of the DBMSs provide the security sub-system, which the DBA uses to create accounts of users and to specify account restrictions. The user enters his/her account number (or username) and password to
access the data from database. For example, if you have an account of e-mail in
the "hotmail.com" (a popular website), then you have to give your correct
username and password to access your account of e-mail. Similarly, when you
insert your ATM card into the Auto Teller Machine (ATM) in a bank, the machine
reads your ID number printed on the card and then asks you to enter your pin
code (or password). In this way, you can access your account.
7. Data Atomicity:
A transaction in commercial databases is referred to as atomic unit of work. For example, when you purchase something from a point of sale (POS) terminal, a number of tasks are performed such as;
- Company stock is updated.
- Amount is added in company's account.
- Sales person's commission increases etc.
All these tasks collectively are called an atomic unit of work or transaction.
These tasks must be completed in all; otherwise partially completed tasks are
rolled back. Thus through DBMS, it is ensured that only consistent data exists
within the database.
8. Database Access Language:
Most of the DBMSs provide SQL as standard database access language. It is used
to access data from multiple tables of a database.
9. Development of Application:
The cost and time for developing new applications is also reduced. The DBMS
provides tools that can be used to develop application programs. For example,
some wizards are available to generate Forms and Reports. Stored procedures
(stored on server side) also reduce the size of application programs.
10. Creating Forms:
Form is very important object of DBMS. You can create Forms very easily and
quickly in DBMS, Once a Form is created, it can be used many times and it can be
modified very easily. The created Forms are also saved along with database and
behave like a software component.
A Form provides very easy way (user-friendly interface) to enter data into
database, edit data, and display data from database. The non-technical users can
also perform various operations on databases through Forms without going into
the technical details of a database.
11. Report Writers:
Most of the DBMSs provide the report writer tools used to create reports. The users can create reports very easily and quickly. Once a report is created, it can be used many times and it can be modified very easily. The created reports are also saved along with database and behave like a software component.
12. Control Over Concurrency:
In a computer file-based system, if two users are allowed to access data simultaneously, it is possible that they will interfere with each other. For example, if both users attempt to perform update operation on the same record, then one may overwrite the values recorded by the other. Most DBMSs have sub-systems to control the concurrency so that transactions are always recorded" with accuracy.
13. Backup and Recovery Procedures:
In a computer file-based system, the user creates the backup of data regularly to protect the valuable data from damaging due to failures to the computer system or application program. It is a time consuming method, if volume of data is large. Most of the DBMSs provide the 'backup and recovery' sub-systems that automatically create the backup of data and restore data if required. For example, if the computer system fails in the middle (or end) of an update operation of the program, the recovery sub-system is responsible for making sure that the database is restored to the state it was in before the program started executing.
14. Data Independence:
The separation of data structure of database from the application program that is used to access data from database is called data independence. In DBMS, database and application programs are separated from each other. The DBMS sits in between them. You can easily change the structure of database without modifying the application program. For example you can modify the size or data type of a data items (fields of a database table).
On the other hand, in computer file-based system, the structure of data items are built into the individual application programs. Thus the data is dependent on the data file and vice versa.
15. Advanced Capabilities:
DBMS also provides advance capabilities for online access and reporting of data
through Internet. Today, most of the database systems are online. The database
technology is used in conjunction with Internet technology to access data on the
web servers.
Disadvantages of Database Management System (DBMS):
Although there are many advantages but the DBMS may also have some minor
disadvantages. These are:
1. Cost of Hardware & Software:
A processor with high speed of data processing and memory of large size is
required to run the DBMS software. It means that you have to upgrade the
hardware used for file-based system. Similarly, DBMS software is also Very
costly.
2. Cost of Data Conversion:
When a computer file-based system is replaced with a database system, the data
stored into data file must be converted to database files. It is difficult and
time consuming method to convert data of data files into database. You have to
hire DBA (or database designer) and system designer along with application
programmers; Alternatively, you have to take the services of some software
houses. So a lot of money has to be paid for developing database and related
software.
3. Cost of Staff Training:
Most DBMSs are often complex systems so the training for users to use the DBMS
is required. Training is required at all levels, including programming,
application development, and database administration. The organization has to
pay a lot of amount on the training of staff to run the DBMS.
4. Appointing Technical Staff:
The trained technical persons such as database administrator and application
programmers etc are required to handle the DBMS. You have to pay handsome
salaries to these persons. Therefore, the system cost increases.
5. Database Failures:
In most of the organizations, all data is integrated into a single database. If
database is corrupted due to power failure or it is corrupted on the storage
media, then our valuable data may be lost or whole system stops.
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