Page 73 - CITS - Computer Software Application -TT

COMPUTER SOFTWARE APPLICATION - CITS

1 Weak Entity
A weak entity is an entity that relies on another entity. Unlike a strong entity, a weak entity lacks its own key
attribute. It is depicted using a double rectangle in diagrams.
Example: A corporation has the ability to retain data regarding the family members (parents, children, spouse) of
an employee. However, these family members only hold significance due to their connection with the employee.
Consequently, family members are categorized as a vulnerable entity type, while employees are recognized as
the pivotal entity type for the family members, indicating that they are..
2 Strong Entity

A Strong Entity refers to an entity possessing a primary Attribute. It maintains independence from other entities
within the Schema, boasting a primary key that facilitates its distinct identification. This is symbolized by a
rectangle and is termed as a Strong Entity Type.

Attributes
Attributes are the characteristics that establish the nature of an entity type. For instance, attributes like Roll
Number, Name, Date of Birth, Age, Address, and Mobile Number serve to characterize the entity type of Student.
Within an Entity-Relationship (ER) diagram, attributes are depicted using oval shapes.
1 Key Attribute
The key attribute is the distinctive characteristic that identifies each individual entity within the set of entities. For
instance, the Roll_No serves as a unique identifier for every student. In an Entity-Relationship (ER) diagram,
this key attribute is depicted as an oval shape containing underlying lines.

2 Composite Attribute
A composite attribute is formed by combining multiple individual attributes. An illustration of this is the student
Entity type’s Address attribute, which encompasses Street, City, State, and Country. Within an ER diagram, a
composite attribute is symbolized by an oval containing smaller ovals

3 Multivalued Attribute
A characteristic that holds multiple values for
a specific entity. For instance, Phone_Number
(which can have multiple entries for a single
student). In an Entity-Relationship (ER) diagram,
a multivalued attribute is depicted using a pair of
connected ovals.
4 Derived Attribute
An attribute that is obtained based on other
attributes within the entity type is referred to as
a derived attribute. For example, Age (calculated
from Date of Birth). In an ER diagram, a derived
attribute is depicted using a dashed oval.
The Student entity type along with its attributes can
be illustrated as follows:

Relationship
A relationship is utilized to define the connection between entities. In graphical representations, such as in an ER
diagram, this relationship is symbolized using a diamond or rhombus shape.

Types of relationship are as follows:

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CITS : IT&ITES - Computer software application - Lesson 18 - 36