UML Diagram Tutorial: A Complete Guide to UML Diagrams

This comprehensive guide to UML Diagrams explains what is a UML Diagram, its uses, types, and compares UML vs ER Diagram:

A UML diagram can be helpful to businesses and other individuals who wish to simplify the development process. Diagrams allow individuals to brainstorm ideas, make plans, and communicate.

A community called “visual illustrations of a software or business model” comprises participants from virtually every discipline today. UML is a part of a unified model specifically used to describe, document, and pinpoint the flaws and errors in a business model or software system.

Besides this, there is so much to learn about UML Diagrams.

Let’s delve into it a little bit further.

UML Diagram Guide

UML Diagram Guide

Unified Modeling Language is the term for UML. It defines a specific architecture, design, and implementation of a complex software system. UML is a visual representation of a software program that uses a series of diagrams. By using standard engineering practices that have proved effective over the years, large and complex systems can be effectively modeled.

In UML diagrams, a general-purpose language, or model, is used to communicate software design. It simplifies communication and allows you to visualize the model. Software systems have many subcomponents and thousands of lines of code, making it difficult to keep track of their relationships. Unified Modeling Language diagrams enable you to see these relationships.

An object-oriented and software development process cannot be successful without the UML. Software project designs are expressed in the UML mainly via graphical notations. The UML facilitates communication, exploration of potential designs, and validation of the software architecture design.

What are UML Diagrams

Unified Modeling Language diagrams serve to describe, analyze, discover, and test a system’s characteristics, behaviors, and other features.

A UML diagram is created before, during, and after coding an application to better understand the roles, activities, and workflows involved in the application. Using the diagram, possible errors in the design can be easily detected, resulting in a better-quality final product.

Unified Modeling Language Uses

UML diagrams are widely used in software engineering and other business processes where model-based decisions are useful.

When used in these processes, UML diagrams contribute in two main ways:

  • Forward design: Coding the software application occurs after the modeling and design has been completed. When creating a new system, a developer uses forward design to think about what they want to achieve.
  • Backward design: Modeling occurs after the code has been written, and UML diagrams serve as an important tool to document the project’s workflow. The developer can then analyze the project development, in reality, to see where improvements can be made to make it better in the future.

It provides a visual representation of many aspects of a project and identifies who is responsible for which part of it. It can be prepared before or after coding.

UML Diagram Symbols

Each type of UML diagram uses different symbols. The class diagram represents the attributes of a class in UML diagrams and is a common type.

In the UML class diagram, a class’s responsibilities, operations, and attributes are represented by segments.

Notations of UML class members indicate whether members are visible.

UML Diagram Symbols1 new

Relationships between components can also be shown with lines:

  • An empty arrowhead denotes generalization and inheritance. A filled diamond indicates composition.
  • Diamonds indicate aggregates, whereas dashed lines with arrows represent dependencies.
  • The properties of a dependency can be specified with << >>. An arrow with a number and a * denotes multiplicity.

Below diagram shows various relationship arrows:

various relationship arrows in UML

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It is easy to recognize packages from their symbols in package diagrams.

Package Diagram1

Most activity diagrams show symbols representing activity types, states, and an initial state as well as a final state. In most control flow diagrams, arrows depict control flow, and dashed arrows represent object flow.

activity diagrams

Users can identify actors and use cases using Use Case diagrams.

Types of UML Diagrams

There are 14 types of Unified Modeling Language diagrams. These diagrams are divided into behavioral and structural diagrams according to their functions.

  • Structural Diagrams: These diagrams describe the structure or statics of a system. Among the Structure, Diagrams are the Component diagram, Object diagram, Package diagram, Class diagram, and Deployment diagram.
  • Behavior Diagrams: Behavioral UML Diagram examples depict how the system behaves dynamically. A behavior diagram includes Use Case diagrams, State diagrams, Activity diagrams, Interaction Overview diagrams, Sequence diagrams, State diagrams, Communication diagrams, and Timing diagrams,

Structural Diagrams

This system shows the different objects in a structured way, or it can be said that the different objects are displayed contextually.

#1) UML Class Diagram

A class diagram is the backbone of any object-oriented solution since it shows the hierarchy of a system. There is a relationship between the attribute, object, operation, and even classes.

The class is further divided into three parts:

  • The top part consists of the name.
  • The bottom part consists of the operation.
  • The middle part consists of the attributes.

These classes are grouped to create a class diagram. The below UML class diagram example shows the Organization structure.

Class Diagram

#2) Package Diagram

In the package diagram, you will identify the dependencies between the various packages available. Package importation and package merging are examples of a dependency between packages. Therefore, this diagram can be used to represent different software systems.

Further, it is possible to find insights into layers’ communication mechanisms from the dependencies between packages.

For example, below is a simple package diagram showing three packages – Invoice, Accounts, and Employee, and it also shows dependency (‘uses’) between them.

Package Diagram

#3) Object Diagram

Like the class diagrams, the object diagram also shows the relationship between the objects used in the real world. A diagram can explain the relationship between the objects with great precision since the data is contained in the objects.

However, the object diagram is more specific than the class diagram. It will show the complete view of the structure in the customized system at a specific time.

Object Diagram

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#4) Component Diagrams

The component structure diagram shows the relationships between different software system components. This complex system contains several components and is used when working with complexities alone.

The component even communicates with each other with the help of interfaces, as the interface is connected with the connectors that help them communicate.

Below is a component diagram for the Library management system:

Component Diagram

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#5) Deployment Diagram

The deployment diagrams show the hardware of the system and the software in that hardware. A graph can be useful when a software solution is distributed across multiple machines and has a unique configuration. It shows where the pieces of the solution are interconnected.

Below is an example of a deployment diagram for hospital management software:

Deployment Diagram1

#6) Profile Diagram

Profile diagrams are a new type of diagram introduced in UML 2. This is a diagram that is rarely used in specifications. In the metamodel levels, stereotypes appear as classes and profiles as packages. Before introducing the profile diagram, there were several other diagrams for displaying any issue.

Profile Diagram

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#7) Composite Structure Diagram

Simply, the composite structure diagram is used to show the internal structural class. It is a type of static structure diagram that will show the collaboration possible under this structure.

In this diagram, you can even find the internal parts, and ports also, through which different parts interact with each other or with the outside world. It is the set of interconnected elements to achieve some purposes.

Composite Structure Diagram

Behavioral Diagram

A behavioral diagram depicts activities and interactions that will occur within the system. Understanding the relationship between these objects helps in constructing a functional system.

#1) Activity Diagrams

Activity diagrams indicate the workflow of the business graphically. It is an easier way to explain to others. It can describe the operational workflow or business workflow in a system. These activity diagrams are also an alternative to state machine diagrams. It encompasses both organizational processes and computations, along with the data flows connected to related activities.

Below is the Activity diagram for online shopping:

UML Activity Diagram

#2) Sequence Diagrams

Sequence diagrams represent how objects will intersect each other, in what order, and as a result, what is taking place. Intersections are represented by arrows, while processes are represented vertically.

A sequence of messages is exchanged between individuals and used to determine the functionality of the scenario.

Below is the Sequence diagram for the Online exam system:

Sequence Diagram

#3) Use Case Diagrams

A use case is similar to the other types of behavioral diagrams because it also provides a graphical overview of the components that are involved within the system.

It describes the different functions that come into play and describes how these factors interact. This is an excellent point for starting a discussion since the actors can identify.

Use Case Diagram

#4) Interaction Overview Diagrams

In the interaction overview diagram, the sequence of processes is also shown as in the activity diagram. They are somewhat similar to the activity diagram in that they show the sequence of the interaction diagram. There are seven types of interaction diagrams in general. It shows the sequence of intersection diagrams and the order of events.

Interaction Overview Diagram

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#5) Timing Diagrams

Timing Diagrams are somewhat similar to sequence diagrams, as they represent the object’s behavior in the given time. The diagram can be considered straightforward if the diagram has only one object. If it has over one object, it may involve a timing diagram showing the interaction between the different objects during the specific time frame.

Timing Diagram

#6) State Machine Diagrams

Activity diagrams and the state machine diagram are similar to one another. But the usage and notation can be changed a bit. The state machine diagrams are also known as state diagrams or state chart diagrams. It can describe the object’s behavior that is acting differently but will be according to its state.

State Machine Diagram1

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#7) Communication Diagrams

A communication diagram can also be described as a collaboration diagram. Communication diagrams are similar to sequence diagrams, but the focus is only on the messages that have been passed between objects in the diagram. Likewise, the same information presented will also be illustrated using a sequence diagram and different objects.

Communication Diagram

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UML vs. ER Diagram

The below table will explain the differences between the two:

Unified Modeling language (UML) Entity Relationship Diagram
DefinitionUML diagrams represent the main objects used in software development, and allow visualization of these objects. This is also referred to as a blueprint for how an application will be built.In ER diagrams, the objects and their relationships are represented graphically.
RelationshipsUML diagrams are supersets of ER diagrams. The ER diagram corresponds to the UML diagram.
UsageDesign and tracking the entire software architecture are done with it. In it, database designs and implementations are handled.

Entity Relationship Diagram1

Also, Read =>> Guide to the Entity-Relationship Diagram

UML Diagram Example (Hospital Management)

Generally speaking, Hospital Management Systems are large systems that require several modules and subsystems to accomplish so many tasks. This application will train hospital receptionists in UML diagram examples.

The Hospital Reception module or subsystem coordinates the schedule of appointments, admissions to the hospital, and other duties of the hospital receptionist. The receptionist has many job duties, such as scheduling appointments, admitting patients to the hospital, and leading family meetings.

Patients in the hospital will need to be assigned to a ward. They collect patient information and note everything, such as arrivals and departures, as part of their job. A receptionist also has to receive the payments from the patient, keep their record, and provide the receipt to the customers. They even have to file medical reports and insurance claims.

All these tasks are done by the receptionist alone, and that is explained here adequately with classifications and everything. With the help of one of the UML class diagram examples, you can understand things in a better way where all the work of the hospital receptionist is outlined.


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Frequently Asked Questions

Q #1) What is UML used for?

Answer: UML (Unified Modeling Language) is a modeling language for software developers. It can be used to develop diagrams and provide class diagram examples of expressive modeling for users (programmers). The UML tool can generate code in the target language.

Q #2) Is the flowchart a UML diagram?

Answer: A UML activity diagram is a representation of unified modeling. Contrary to this, a flowchart illustrates an algorithm graphically.

Q #3) Which UML diagram is best?

Answer: Use Case Diagram apart from a Class diagram & a sequence diagram on UML will work best if you’re a developer.

Q #4) Which are the 3 models in UML?

Answer: UML categorizes modeling in three different ways:

  • Structural modeling: This encapsulates a system’s static characteristics
  • Behavioral modeling: This model intends to focus on the system’s functioning.
  • Architectural modeling: A system’s overall framework is represented in it.

Q #5) Why is UML called a language?

Answer: It is an open-source modeling language. Using UML diagram Java, you can visually model the design of a system. Blueprints are also used in other engineering fields. UML diagrams do not represent programs but visual representations.


A UML diagram may help document processes and systems, as you’ve probably noticed. Creating one may seem challenging at first since it is so complex. The syntax must be learned, the diagram types must be chosen, and so on. The mapping process or system becomes more apparent when you think about UML standards.

Last, UML diagrams help you identify flaws or make optimization suggestions that you otherwise wouldn’t have noticed. We hope to help you understand how UML diagrams can benefit your organization through this article.