Review of theory of database

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Review of Theory of Databases

Review of Database Concepts



What is a Database? A database is a collection of logically related data.

Example: Personal information such as name, address, birthday and gender

What is a Schema? A schema or a database schema is the over-all design of a

database.

What is a Database System? A database system is an automated system that enables users

to define, create, maintain and control access to the database.



What are the components of the DBMS Environment?

Data Hardware Software End Users Procedure



What are the different facilities that DBMS provide?

Users can define the database through a Data Definition Language (DDL).

Users can manipulate data through a Data Manipulation Language (DML).

DBMS can provide security system. DBMS can provide an integrity system. DBMS can provide a concurrency control system. DBMS can provide a recovery control system.



What are the different entity relationships? One-to-One

Table A Table B

A1

A2

A3

A4

B1

B2

B3

B4



What are the different entity relationships? One-to-Many

Table A Table B

A1

A2

A3

B1

B2

B3

B4

B5



What are the different entity relationships? Many-to-One

Table BTable A

B1

B2

B3

A1

A2

A3

A4

A5



What are the different entity relationships? Many-to-Many

Table A Table B

A1

A2

A3

A4

B1

B2

B3

B4



What is relational database? A relational database is divided into logical units

called table which is composed of rows and columns of data.



What is a relation? A relation is composed of rows and columns of data.

What is an attribute? In relational database, the table columns correspond to

attributes. What is a domain?

A domain refers to a set of valid atomic values for a given attribute.

What is a primary key? A primary key refers to an attribute or field that serves as

a unique identifier for a particular record within a relation.



What is SQL? Structured Query Language (SQL) is the standard

language used to define, query, update and maintain relational databases.

Main categories of SQL commands are as follows: Data Definition Language (DDL) Data Manipulation Language (DML) Data Query Language (DQL) Data Control Language (DCL) Transactional control commands



What is Data Definition Language (DDL)? The DDL allows the user to create and restructure database

objects. Some of the most fundamental DDL commands are:

CREATE TABLE ALTER TABLE DROP TABLE CREATE INDEX ALTER INDEX DROP INDEX CREATE VIEW DROP VIEW



What is Data Control Language (DML)? DML allows the user to manipulate data within objects of

a relational database. The three basic DML commands are

INSERT UPDATE DELETE

What is Data Query Language (DQL)? DQL allows the user to select a data or a group of data. The base command is SELECT



What is Data Control Language (DCL)?

The DCL allows the user to create objects related to user access and also control the distribution of privileges among users.

Some data control commands are as follows:

ALTER PASSWORD GRANT REVOKE CREATE SYNONYM



What is Transactional Control Commands (TCC)? The TCC allow the user to manage database

transactions. Some commands are as follows:

COMMIT ROLLBACK SAVEPOINT SET TRANSACTION



What is Integrity Constraint? Integrity constraints are used to ensure accuracy and

consistency of data in a relational database.

What are the types of integrity constraints? Primary key Constraints Unique Constraints Foreign Key Constraints Not Null Constraints Check Constraints



What is normalization?

Normalization is a process of reducing data redundancy in a database.

The different levels of normal forms:

First Normal Form (1NF) Second Normal Form (2NF) Third Normal Form (3NF)



What are the advantages of normalization?

Better overall database organization Reduction of redundant data Data consistency within the database Flexible database design Efficient database security handling Enforces concept of referential integrity

Review of theory of database

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