Lesson 2 Entity Relationship Model

The Entity Relationship Model consist of the following component

a) Entity
b) Attributes 
c) Relationship 
d) Key Attributes

a) Entity 
An entity is class object event or concepts about which we need collect and store data.

• note

Entity is a thing which can be easily identified. An entity is any object, place, person or activity about which data is recorded.

• Person: - Employee, Student, Vender….
• Place: - Branch, Office, Building, room….
• Object: - Book, Machine, Pen…..
• Event: - Sell, Purchase, Registration…

b) Attributes An attributes is a property of given entity.

roll number is a property of an entity student.

NOTE
In dbms there are many words for a same thing

means as above i said field and then I said entity, some time its called columns, DON'T GET PUZZLED IN THAT
this is only the way some kind of differentiating different environments 
for example ROWS, RECORDS and TUPLES 
If you talking in RDBMS (Relational Data Base Management System) we called them TUPLES.
If you talking in DBMS (Data Base Management System) we called them RECORDS.
If you talking in MS EXCELL we called them ROWS.

=========================================
Column, Fields, Attributes

Column :- In EXCELL
Fields:- In DBMS
Attributes:- in E-R DIGRAM 
=======================================
Entity, Table, File

Entity:- In E-R DIGRAM
Table :- When we create/edit an ENTITY in form of Table.
File :- when data stored in hardware (hard disk)


WE ALWAYS GET PUZZLED IN DIFFERENT WORDS BUT WITH THE SAME MEANING.
Please Comment me Below or E-mail me @ harshkumar2009@gmail.com.