(ER model)

 

Name : Ahmed Ameen Althulaia

Roll no : 4

GR no : 11911223

Group no : 2

 

Introduction

The ER Model represents the Entity-Relationship Model, also known as a high-level data model that reflects relationships between business sets.ER Model is used to describe businesses and relationships between them.

 

It helps developers to design conceptual design or not to specify system intelligent design from a data point of view.The ER model describes the design of a site with the help of a diagram, also known as a Business Diagram (ER Diagram).

 

ER Diagram

The ER diagram shows the relationship between business sets. A business set is a group of similar businesses and these businesses may have characteristics. According to the DBMS, a business is a table or table attribute on a website, so by showing the relationship between tables and their attributes, the ER diagram shows the complete logical structure of a website. Let’s take a look at a simple ER diagram to understand this concept.

 

ER Models in Database Design

They are widely used to design database relationships. Businesses in the ER schema become tables, attributes and modify the database schema. As they can be used to visualize website tables and their relationships are often used to solve a problem on a website.

 

Drawings of business relationships in software engineering

Business relationship diagrams are used in software engineering during the planning stages of a software project. They help identify different system elements and their relationships with each other. It is often used as the basis for data flow diagrams or DFDs as they are widely known.

 

For example, inventory software used in a retail store will have a website that monitors features such as purchase, item, item type, item source and item price. Providing this information with an ER diagram can be something like this:

In the diagram, the information inside the oval shapes are attributes of a particular entity

 

Entity Relationship Diagram (ERD) Symbols and Notations

There are three basic elements in an ER Diagram: entity, attribute, relationship. There are more elements which are based on the main elements. They are weak entity, multivalued attribute, derived attribute, weak relationship, and recursive relationship. Cardinality and ordinality are two other notations used in ER diagrams to future define relationship.

Entity

An entity can be a person, place, event, or object that is relevant to a given system. For example, a school system may include students, teachers, major courses, subjects, fees, and other items. Entities are represented in ER diagram by a rectangle and named using singular nouns.

Weak Entity

A weak entity is an entity that depends on the existence of another entity. In more technical terms it can be defined as an entity that cannot be identified by its own attributes. It uses a foreign key combined with its attributed to form the primary key. An entity like order item is a good example for this. The order item will be meaningless without an order so it depends on the existence of the order.

Attribute

An attribute is a property, trait, or characteristic of an entity, relationship, or another attribute. For example, the attribute Inventory Item Name is an attribute of the entity Inventory Item. An entity can have as many attributes as necessary. Meanwhile, attributes can also have their own specific attributes. For example, the attribute “customer address” can have the attributes number, street, city, and state. These are called composite attributes. Note that some top level ER diagrams do not show attributes for the sake of simplicity. In those that do, however, attributes are represented by oval shapes.

Multivalued Attribute

If an attribute can have more than one value it is called a multivalued attribute. It is important to note that this is different from an attribute having its own attributes. For example, a teacher entity can have multiple subject values.

                 

 

Derived Attribute

An attribute based on another attribute. This is found rarely in ER diagrams. For example, for a circle, the area can be derived from the radius.

                                       

Relationship

A relationship describes how entities interact. For example, the entity “Carpenter” may be related to the entity “table” by the relationship “builds” or “makes”. Relationships are represented by diamond shapes and are labeled using verbs.

How to Draw ER Diagrams

1.   Identify all the entities in the system. An entity should appear only once in a particular diagram. Create rectangles for all entities and name them properly.

2.   Identify relationships between entities. Connect them using a line and add a diamond in the middle describing the relationship.

3.   Add attributes for entities. Give meaningful attribute names so they can be understood easily.

 

Benefits of ER diagrams

ER diagrams form a very useful framework for creating and modifying information. First of all, ER drawings are easy to understand and do not require extensive training to be effective and efficient. This means that designers can use ER graphics to easily communicate with engineers, customers, and end users, regardless of IT expertise.

 

Second, ER diagrams are easily translated into related tables that can be used to quickly create information. Additionally, ER graphics can be used directly by web developers as a data usage plan for specific software applications.

 

Finally, ER diagrams can be used in other contexts such as describing different relationships and operations within an organization.