DBMS Summary:
Chapter 1
1.) File Base System
A
collection of application programs that perform services for the end-users such
as production of reports. Each program defines and mange its own data.
2.) Limitation of the File-Based Approach
- Separation and
isolation of data
- More difficult to access the data
when data is isolated in separate files.
- Difficult processing when data
are in difference files.
- Duplication of Data
- is wasteful. It cost time
and money to enter the data more than once.
- It
takes up additional storage space, again with associated cost. Duplication can
avoid by sharing files.
- Lead
to loss of data integrity. The data is no longer consistent. For example the
payroll and personnel department if a member staff moves house and the change
address is communicated only to personnel and not to Payroll. So the person pay
check will sent to the wrong address.
- Data dependence
Changes of existing
structure are difficult to make. Not flexible and hard to maintain. Because if
changes one it will effect to others.
-Incompatible file
formats
The structure of files is
embedded in the application programs; the structures are dependent on the
application programming languages. For example structure of a file generated by
cobol program maybe different from structure of file generated by c program.
The
incompatibility is files make them difficult to process jointly.
-Fixed
queries/proliferation of application programs.
There was no provision for
security or integrity.
Recovery,
in the event of a hardware or software failure, was limited or non-existent;
Access
to the file was restricted to one user at a time. There is no provision shared
access by staff in the same department.
3.)
Database: A shared collection of logically related data, and a
description of this data, designed to meet the information needs of an
organization.
The database represents the entities, the attributes, and
logical relationships between the entities.
4.) DBMS: A
software system that enables users to define, create, maintain, and control
access to the database.
The DBMS is the
software interacts with user’s application program and the database.
-
Allow user define database by DDL (Data
Definition Language) DDL allow users to specify data types and structures and
the constrains on the data stored in the database.
-
Allow insert, delete, update and retrieve data
from database by DML(Data Manipulation Language). DML use query language the
common query language is SQL.
-
Provide control access to database
o
Security system
o
Integrity system maintains the consistency of
stored data.
o
A concurrency control system allows shared
access of the database.
o
Recovery control system restore the database
o
A user-accessible catalog contains description
of data in the database.
5.) Application
Programs
A computer program that
interacts with the database by SQL statement to the DBMS.
Views
Views
provide security. Views can exclude data that some users should not see.
Views
provide a mechanism to customize the appearance of the database.
Views
can present a consistent.
Component of DBMS
Hardware, Software, Data
(schema, tables, attributes, relationship), People and
Procedures
Log on to the
DBMS
Application
programs
Start & Stop
DBMS
Make backup
copies of database
Handle software
and Hardware failure. Change the structure of table.
Advantage of DBMS
-
Control of data redundancy
-
Data consistency ស្ថិរភាព
-
More information from the same amount of data,
sharing of data
-
Improved data integrity
-
Improved security
-
Enforcement of standards
-
Economy of scale
-
Balance of conflicting requirements
-
Improved data accessibility and responsiveness
-
Increased productivity
-
Improved maintenance through data independence
-
Increased concurrency
-
Improved backup and recovery services.
Disadvantage of DBMS
C Complexity , Size, Cost of DBMS, Additional Hardware cost,cost of conversion,performance, higher impact failure.
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