The Main Building Modules of the Entity Relationship Model

1. What are the main building modules of the Entity Relationship model? Discuss each one.
The Entity-Relationship model is a top-down approach to design database that is based on uniquely identifiable object. If begins by identifying things that are uniquely distinguishable called entities and relationships among these entities.
The main building modules of the Entity-Relationship model are: a. Entities b. Relationships c. Attributes
Entities
An Entity is a basic object of ER-model which is an object in real world that can be distinguishable and can exists independently.
Relationships
Relationship defines the association among two entities. Suppose, consider student and a class are the two entities. These entities are associated as “student studies in class”. Hence studies is a relationship between the two entities, student and class.
Attributes
The properties of the entities are called attributes.
For example if we consider a mobile phone as an entity then each mobile well have its own color, design, model company. All these are the attributes of the mobile entity.

2. What is a weak entity, and how is it represented in an E-R diagram? Give an example.

Weak entity is the one that depends on other entities for existence.
A weak entity cannot be identifies uniquely as it does not have sufficient entities to form a primary key. To make it uniquely unidentifiable, weak entity set is associated with another entity set, called identifying or owner entity set. The owner entity set “OWNs” the weak entity set. The relationship among the two entity sets is called identifying relationship. The identifying relationship is always many-to-one and its participation is total.
Although weak entity set is not provided with a primary key, there is always a need to distinguish among attributes in weak entities. The discriminator is a set of attributes that