DBMS Training & SQL Tutorial :
Introduction to Database Management
Theory you need to know!
Database Concepts :
A database consists of a number of tables. Each table comprises of rows(records) and columns(attributes). Each record contains values for the corresponding attributes. The values of the attributes for a record are interrelated. For example, different cars have different values for the same specifications (length, color, engine capacity, etc.).
In the database oriented approach, we store the common data in one table and access it from the required tables. Thus the redundancy of data decreases.
The database oriented approach supports multiple views of the same data. For example, a clerk may only be able to see his details, whereas the manager can view the details of all the clerks working under him.
Multiple views of the same database may exist for different users. This is defined in the view level of abstraction.
The logical level of abstraction defines the type of data that is stored in the database and the relationship between them.
The design of the database is known as the database schema.
The instance of the database is the data contained by it at that particular moment.
The Database Administrator has the total control of the database and is responsible for the setting up and maintaining the database.
The DDL (Data Definition Language) is used to define the schema of the database and relations between entities.
The DML (Data Manipulation Language) enables us to access and operate upon the data in the database.
The DCL (Data Control Language) is used to control the access to the database.
The Procedural DML requires the user to state the information required and how to get it whereas the Non-Procedural DML does not require the user to specify how to get the information.
The query processor breaks down the DML statements into statements that can be comprehended by the DBMS.
A transaction is a collection of commands that together perform a particular task. For example, a transaction to transfer funds from one bank account to another includes debiting one account and crediting the other account with the same amount.
Transaction Management must satisfy the properties of Atomicity,Consistency,Isolation and Durability (ACID)
The property of atomicity in transaction management ensures that either the entire transaction occurs completely or does not occur at all.
The property of durability in transaction management ensures that the new values of the database persist across system failures.
The storage manager interfaces between the actual data that is stored by the database and the application programs that submit the queries.