1)What is database?
Database is a collection of related data and data is collection of facts and
figures that can be processed to produce information.
2) What is DBMS
A Database Management System stores the data in such a way that
it becomes easier to retrieve,manipulate and product information.
3) What is ER Model?
Entity-Reletionship (ER) model is based an the notion of realt word entotoes and reletionship among them. ER model is best used are the conceptual design of a database.
ER model is based on :
- Entities and their attributes
- Relationship among entities
- Entity :-
An entity in an ER-model is a real word entity having properties called attributes.
Every attributes is defined by the set of values called domen.
Example:–
dataase-student(school database )whear
Entity :- Student
Attribute:-name,age,class,etc.
- Relationship :-
The logical association among entities is colled Relationship. Relationship mapped with entities in various ways.
Mappomg cordinaties:-
- one to one
- one to many
- many to one
- many to many
4) Types of keys:
Thea are various types of keys in a relationship which are :
Candidate key:-
The minimal set of attributes which can determine a tuple uniquely. There can be more than i candidate key of a relation and its proper subset can’t determine tuple uniquele and it can’t be null.
Super key :-
The set of attributes which can determine a tuple uniquely.A candidate key is always a supeer key but super key will not be candidate key always.
Primary key :-
Among various candidate keys, one key is taken as primary key which is unique and other is alternate key.
Foreign key:-
Foreign key is a set of attributes in a table which is used to prefer/refor the primary key or alternative key of the same or other table.