Critical Thinking

GETTING represents the logical structure of an database.

GETTING FAMILIAR WITH TERMS

1.    ER MODEL : The entity relationship data model on a perception of a real world that
consists of a collection of basic objects called entities and of relationships
among them. This represents the logical structure of an database.

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2.    ENTITIES : An entity is a thing in the real world that is distinguishable from all
other objects.

3.    ATTRIBUTES : An entity is represented by a s et of attributes. These are descriptive
properties possessed by each member of the entity set.

4.    RELATIONSHIP SETS : A relationship set is a set of relationships of the same type.

5.    CONSTRAINTS : An E-R enterprise schema may define certain constraints to which the
database must conform.

6.    ENTITY SETS : A superkey is a set of one or more attributes that taken
collectively,allow us to identify uniquely an entity in an entity set.

7.    N-ARY RELATIONSHIPS : Generally the relationships are binary, sometimes the database has more
than one entity, so they have tertiary or n-ary relationships. This particular
model is a tertiary relationship (three entity sets).

8.    MAPPING CARDINALITIES :

?     
ONE-TO-ONE : Every entity in each of the two
entity set are at most related to one entity each.

?     
ONE-TO-MANY: An entity in customer is associated
with a number of entities in order.But Any entity in order can have at most one
entity in customer.

?     
MANY-TO-ONE: An entity in set A is associated
with at most one entity in B. But Any entity 
in B can be associated with a number of entities in A.

?     
MANY-TO-MANY: An entity in product can be
associated with a number of entities in order and vice versa is also true.

9.    AN E-R DIAGRAM COMPOSES OF
THESE MAJOR COMPONENTS :

?    
RECTANGLES – Entity sets (
CUSTOMER, PRODUCT, ORDER)

?    
ELLIPSES -Attributes
(C-ID,FIRSTNAME,LASTNA

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