Data Base : COMPONENTS OF A DBMS

What is a DBMS?
DBMS (or Database Mgmt System).A software for creating and managing large databases efficiently.
.E.g.
-Oracle
-MSAccess
-Sybase

Real Business: What is a DBMS
Database management systems:
Provide efficient and secure access to large amounts of data.
Address problems such as:
How to store the data
How to query data efficiently
How to update the data securely (by multiple users)
Contrast with using file systems for the same task

Database Industry
-Relational databases are a great success of theoretical ideas.
-“Big 3” DBMS companies are among the largest software companies in the world.
-IBM (with DB2) and Microsoft (SQL Server, Microsoft Access) are also important players.
-$20B industry
-Challenged by object oriented DBMS.

Functionality of a DBMS
-Storage management
-Abstract data model
-High level query and data manipulation language
-Efficient query processing
-Transaction processing
-Resiliency: recovery from crashes
-Interface with programming languages

Why Use a DBMS?
-Data independence and efficient access.
-Reduced application development time.
-Data integrity and security.
-Uniform data administration
-Concurrent access and recovery from crashes.

The Study of DBMS
-Several aspects:
=Modeling and design of databases
=Database programming: querying and update operations
=Database implementation
-DBMS study cuts across many fields of Computer Science: OS, languages, AI, Logic, multimedia, theory...

Need for a DBMS
0To be able to appreciate why we need a DBMS, we must look at what are the limitations of the file processing system (FPS) traditionally used for accessing huge amount of data.
-So, what is a FPS?
=One of the ways to store, manipulate and retrieve large files of data.

For example : a savings bank.
Two types of files
Account File
Customer File.
A separate computer program is written to accomplish the following tasks
Debit or Credit an Account
Add a new account.
Find an account balance.
Generate monthly statements.
Each program defines and manages its own data.
Development of the system proceeds as follows:
New application programs must be written as the need arises.
New permanent files are created as required.


Functions of DBMS
Data Abstraction
The major purpose of a database system is to provide users with an abstract view of the system.
The system hides the details of how data is stored and created and maintained.
There are three levels of abstraction:
Physical Level:
Conceptual Level:
View Level:

Three levels of data abstraction
Physical Schema:
-Is concerned with how the data is stored in the computer’s hard-disk.
E.g. index, B-tree, hashing.
-Lowest level of abstraction.
-Complex low-level structures described in detail.
Conceptual Schema:
-Next highest level of abstraction.
-a detailed specification of the overall structural organization of the data.
-Specifically, what data is stored in the database and the relationships among the data (ER Models).
-Database administrator level.
External Schema or User-View Schema:
-Highest level.
-Describes part of the database for a particular group of users.
-Can be many different views of a database.
E.g. tellers in a bank get a view of customer accounts, but not of payroll data.