The main difference between Class Diagram and Entity Relationship Diagram is that Class Diagram represents the classes and the associations among them in a software program while an Entity Relationship Diagram represents the entities and their relationships between them in a database.
UML (Unified Modeling Language) is a standard modeling language to visualize and document a software system. There are various UML diagrams, and class diagram is one of them. It provides a static view of the system. On the other hand, a database is a collection of related data, which is essential to design a database before developing it. Moreover, entity relationship diagrams help to design a database.
Key Areas Covered
1. What is a Class Diagram
– Definition, Functionality
2. What is an Entity Relationship Diagram
– Definition, Functionality
3. Difference Between Class Diagram and Entity Relationship Diagram
– Comparison of Key Differences
Key Terms
Class Diagram, Entity Relationship Diagram, UML
What is a Class Diagram
A class diagram is a UML diagram. It represents classes and interfaces and how they associate with each other. Furthermore, a class diagram is a static diagram. Therefore, it provides a static view of the application. Also, this is one of the most common UML diagrams as it helps to model Object Oriented Programming concepts.
A rectangle represents a class in a class diagram. It has three rows. The top row has the name of the class while the middle row has the attributes of the class. Thus, these are the properties of the class. The third or the last row, on the other hand, has the methods. They represent the operations the class can use. Furthermore, these methods help to understand how a class interacts with data.
Interactions represent the relationship between the classes. Some common interaction types are inheritance, bidirectional association, and unidirectional association. Inheritance allows the subclasses to use the attributes and methods of the superclass. In contrast, the bidirectional association is the default relationship between the two classes while unidirectional association represents navigation only to a single class.
What is an Entity Relationship Diagram
An Entity Relationship Diagram (ER diagram) helps to design a database. An entity is a real-world object. ER diagram represents the entities and their associations. For example, a hospital database has separate tables for patients, doctors, and medical reports. Each of them is an entity. In the ER diagram, a rectangle signifies an entity. An entity that depends on another entity is a weak entity. Moreover, a double lined rectangle denotes a weak entity.
Each entity has attributes. In fact, an attribute is a property of an entity. For example, the patient can have attributes such as id, name, age, and date of birth. An oval shape represents them. From a set of attributes, one attribute helps to uniquely identify each record. It the primary key. For example, id is the primary key. In the ER diagram, the designer can draw a line under an attribute to denote the primary key in the ER diagram. Furthermore, a foreign key helps to connect two tables. Medical reports table can have a primary key called report id. To link it with the patient, the table can have the patient id as a foreign key. The designer can draw a dashed line under an attribute in order to denote a foreign key in the ER diagram.
A diamond shape or a rhombus represents the association among entities. Moreover, the relationship with a weak entity is called a weak relationship. Furthermore, a double lined rhombus denotes a weak relationship.
There are three types of relationships.
Binary – Signifies the relationship between two entities. It further divides into One to One (1:1), One to Many (1:M) and Many to Many (M: N).
Recursive – An entity connects to itself.
Ternary – Denotes the relationship between three entities.
Difference Between Class Diagram and Entity Relationship Diagram
Definition
A class diagram is a UML type static structure diagram that describes the structure of a system by showing the system’s classes, their attributes and relationships among objects while ERD is a visual representation of data based on the ER model that describes how entities are related to each other in the database. Thus, this is the main difference between Class Diagram and Entity Relationship Diagram.
Usage
Furthermore, another difference between Class Diagram and Entity Relationship DiagramWhile a class diagram helps to understand the static view of the system, an entity relationship diagram helps to recognize the entities and relationships of a database.
Conclusion
In brief, Class Diagram and Entity Relationship Diagram are two common and widely used design diagrams used in software development. The main difference between Class Diagram and Entity Relationship Diagram is that Class Diagram represents the classes and the associations among them in software while an Entity Relationship Diagram represents the entities and their relationships between them in a database.
References:
1.“UML Class Diagram Tutorial.” Lucidchart, Available here.
2.“Working with ER Diagrams.” Types of Network Topology in Computer Networks | Studytonight, Available here.
Image Courtesy:
1.”UML class diagram for Composite software design pattern” By Trashtoy – My own work, written with text editor., Public Domain via Commons Wikimedia
2.”ReaExample” (CC BY-SA 3.0) via Commons Wikimedia
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