UML Diagram in Software Engineering: Types, Uses, and Examples

UML (Unified Modeling Language) is a standardized technique for visualizing the structure and architecture of software systems. For developers, architects, and business analysts, it makes it easier to plan, communicate, and document system components.

In this blog, we will explore the primary UML diagrams and notations and their applications, business process modeling, web and mobile app design, and software development.

Table of Contents:

• What is UML Diagram?
  • Why Do We Use UML?
  • Object Oriented concept in UML
• Types of UML Diagrams
  • Structural UML Diagrams
  • Behavioral UML Diagrams
• UML Diagram Symbols and Notations
• Benefits of UML Diagrams
• When to Use UML Diagrams
• Best Practices for Creating UML Diagrams
• Tools for Creating UML Diagrams
• Steps to create a UML Diagram
• UML in Agile Development
• Use Cases of UML Diagram
• Conclusion

What is UML Diagram?

The Unified Modeling Language (UML) is a method for graphically depicting the architecture, design, and implementation of intricate software systems. An application may contain thousands of lines of code, which can make it difficult to remember links and hierarchies within a software system when writing code. Using UML diagrams, the software system is separated into components and subcomponents.

Why Do We Use UML?

UML (Unified Modeling Language) is basically used to design, visualize, and document the structure and behavior of the system software. Here are some reasons that show why it is adopted by system architects, analysts, and developers:

• Systems Visualisation
  UML provides a standardized method for using diagrams to depict system components and their interactions. This facilitates the simplification of intricate business procedures and software architectures.
• Enhances Interaction
  A common visual language is established by UML diagrams between developers, designers, business analysts, and stakeholders who are not technical. As a result, there are fewer misconceptions during development.
• Better System Design Support
  UML helps in several important ways by modeling systems before implementation. The ways design flaws are identified early, provide a scalable and modular architecture, and schedule component integration in advance.
• Enhances Documentation
  UML serves as a living document that captures system architecture and makes the following tasks easier by introducing new team members, maintaining and updating code, and tracking the development.
• Promotes Reusability and Maintainability
  Modeling promotes reusable components and distinct concern separation, which improves long-term maintainability.
• Supports Different Development Approaches
  UML fits into various development methodologies, like Agile – for iterative and lightweight modeling, Waterfall – for detailed, advanced planning, and DevOps – for virtual representation of infrastructure as code.

Object-oriented concept in UML

Object-oriented programming principles are the core basis of the UML. Through these concepts, the foundation of UML is formed, which represents systems in a modular, maintainable, and scalable way.

1. Classes and Objects
   Classes define the structure and behavior of an object, and the objects are the instances of a class with real values.
2. Encapsulation
   Encapsulation is a property of OOPs that bundles data and methods that operate on the data into a single unit, known as a class, while it restricts direct access to some of the components of the object.
3. Inheritance
   The property of inheritance in OOP is that it allows a subclass to inherit the properties and behavior from a superclass.
4. Polymorphism
   Polymorphism is the property that allows the objects of different classes to be treated as objects of a common class, basically by overriding or overloading.
5. Abstraction
   Abstraction exposes only the necessary features and hides the internal state and behavior of the class.

Types of UML Diagrams

A vast range of diagrams is available in UML to show how a program or system functions in a pictorial format. These diagrams are divided into two groups: structural diagrams and behavioral diagrams. The structural diagram represents the static component of the system. Behavioral diagrams display only the system’s dynamic aspects (interactions, workflows, and state changes).

Structural UML Diagrams

As the name suggests, structural UML diagrams show the classes, objects, packages, components, and other elements of the system along with their relationships between those parts. They are divided into seven parts. They are:

1. Class Diagram: A class diagram is one of the most commonly used UML diagrams. It is the foundation of any object-oriented software system. Class diagrams can be used to show the static nature of a system by showing its classes, along with their attributes (data) and methods (functions). It also helps you to see how different classes or objects are connected or related to each other.

2. Component diagram: Component diagrams are used to show how the physical parts of a system are organized. They are used mainly to model the implementation details of a system. Component diagrams are used to help you understand how different parts of the software are connected and whether the development which is planned meets all the functional requirements. These diagrams are especially useful while designing and building complex systems. Components communicate with each other using interfaces.

3. Deployment diagram: Deployment diagrams are used to show the hardware of the system and the software running on it. They help you to understand what hardware exists and which software components are installed. These diagrams are used to represent the architecture of the system by showing how pieces of software (called artifacts) are distributed across different hardware. Deployment diagrams are especially useful when the software is being used, distributed, or deployed on multiple machines with different setups.

4. Package diagram: Package diagrams are used to show how packages and their contents are organized. They help you to see the dependencies between different packages and what each package contains. Packages make it easier to organize UML diagrams into clear, meaningful groups, which makes the diagrams easier for you to understand. They are used to organize class diagrams and use case diagrams.

Behavioral UML Diagrams

Every system consists of both static and dynamic elements. Consequently, when both elements are thoroughly discussed, a model is said to be complete. In essence, behavioral diagrams demonstrate a system’s dynamic nature. The dynamic aspect of a system refers to its moving and changing components. They are divided into seven parts. They are:

1. Activity Diagram: Activity diagrams are used to show how control flows in a system. You can also use them to represent the steps involved in executing a use case. These diagrams help you visualize both sequential and parallel activities, basically showing workflows in a clear way. An activity diagram focuses on the conditions that guide the flow and the order in which things happen. It also helps explain what triggers a particular event in the system.

2. Use Case Diagrams: Use case diagrams are used to show what a system (or part of a system) can do. They are mainly used to represent the functional requirements of the system and how it interacts with external users or agents (called actors). A use case diagram is used to represent different scenarios in which the system can be used. These diagrams give you a high-level view of the system’s functionality without getting into the details of how it is implemented.

3. Sequence Diagram: A sequence diagram is used to show how objects interact with each other in a specific order. This means that it illustrates the sequence of these interactions. Sequence diagrams are also called event diagrams or event scenarios. They are used to explain how the objects in a system work and in what order. These diagrams are commonly used by both business people and software developers to document and understand the requirements of new or existing systems.

4. Communication Diagram: A communication diagram (called a Collaboration Diagram in UML 1.x) is used to show the messages that are exchanged between objects in a specific sequence. These diagrams focus mainly on the objects and how they are connected. While sequence diagrams can show similar information, communication diagrams are used to display objects and their links in a more flexible, free-form layout.

5. Timing Diagram: Timing diagrams are a special type of sequence diagram used to show how objects behave over time. They help you visualize the timing and duration of events that cause changes in the state or behavior of an object.

6. Interaction Overview Diagram: An Interaction Overview Diagram (IOD) is a type of UML diagram that is used to show how interactions happen in a system or process. It provides you with a high-level view of the sequence of actions, decisions, and interactions between different components or objects.

UML Diagram Symbols and Notations

To visually represent software systems, UML uses standard symbols. They are given below

Common UML Element

Relationship Symbols

Benefits of UML Diagrams

The benefits of UML diagrams are

• Simplifies complex ideas and systems
  They make it easier for software engineers to collaborate by visually simplifying abstract concepts and intricate software systems.
• Visualize Complex Code
  Converting complicated lines of code into visual diagrams facilitates software development.
• Keeps Developers on the Same Page
  Communication between team members from different languages and development stages is made easier by UML, a common visual language.
• Improves Cross-Team Collaboration
  Not every programmer knows how to use every programming language and type of code.
• Great for non-technical explanations
  In addition to software engineers, UML diagrams help stakeholders, managers, and product owners understand software processes and functionalities.

When to Use UML Diagrams

• When illustrating the general structure of a system, UML diagrams can promote idea sharing among stakeholders by making it easier to understand how various components interact.
• As you collect and record system requirements, they can assist you in better understanding user demands by showing how users will interact with the system.
• For database designers, class diagrams are a great way to illustrate the relationships between various data entities and ensure that your data model is organized.
• When working with clients or team members, UML diagrams provide a common language for technical and non-technical stakeholders, improving understanding and process alignment.
• Accurately illustrating complex system requirements can be difficult, leading to either oversimplification or excessive detail.
• Inconsistencies and misunderstandings about the model’s purpose may result from different team members’ interpretations of it.
• Maintaining UML diagrams as the system evolves can be very time-consuming, and if done incorrectly, it may lead to outdated representations.
• Agile promotes teamwork, but sometimes UML diagrams are so complicated that only a few people can understand them.

Best Practices for Creating UML Diagrams

System design can be more easily represented and documented with the help of the Unified Modeling Language (UML). Best practices need to be followed in order to produce diagrams that are both important and useful. Here are a few instances of UML best practices:

• Identify the Audience – Consider the people who will view your UML diagrams as you create them.
• Preserve Diagram Simplicity and Focus – Make sure the diagrams you make are as simple as possible.
• Use Consistent Naming Conventions – Provide comprehensible and consistent names for classes, objects, attributes, and methods.
• Follow Standard UML Notations – Ensure that you utilize the same UML notations and symbols.
• Maintain Explicit Relationships – Clearly state and illustrate the connections between various components.

Tools for Creating UML Diagrams

Unified Modeling Language (UML) diagrams, which are frequently used in software development to visually represent system architecture, design, and implementation, can be made with a variety of tools. Here are some well-liked resources:

• Lucidchart – This online diagramming tool is compatible with UML diagrams.
• Draw.io – It is a free online diagramming tool that supports UML and other diagram types.
• StarUML – StarUML is an open-source, user-friendly UML modeling program.
• Visual Paradigm – It provides a variety of software development tools, including UML.

Steps to create a UML Diagram

For creation, there are a number of systematic processes that include the following steps:

Step 1 – Identify the Purpose – Choose the objective for which the UML diagram is being created.

Step 2 – Identify Elements and Relationships – Choose which important elements (classes, objects, use cases, etc.) should be included in the diagram and explain their relationships.

Step 3 – Select the Appropriate Type – Select the type that best suits your modeling requirements.

Step 4 – Create a Rough Sketch – A basic sketch on paper or a whiteboard could be useful before utilizing a UML modeling tool.

Step 5 – Choose a UML Modeling Tool – Choose a UML modeling tool according to your needs.

Step 6 – Create the Diagram – Make a new project or diagram using the UML modeling tool of your choice.

Step 7 – Define Element Properties – Give each diagram element the appropriate traits and attributes.

Step 8 – Add Annotations and Comments – By including annotations, comments, and clarifying notes, you can make the diagram easier to read.

Step 9 – Validate and Review – Verify the accuracy and completeness of the diagram.

Step 10 – Refine and Iterate – Modify the diagram in response to feedback and fresh data.

UML in Agile Development

Agile development and UML (Unified Modeling Language) are two distinct approaches to software development, but they can work in tandem. They have the following relationship:

• UML in Agile Development
  • Visual Communication – They are used to show how the system behaves and is designed.
  • Capturing User Stories – User stories can be captured more easily if UML’s use case diagrams are used to show how users will interact with the system.
  • Building in Steps – By allowing models to be created and updated as the project moves forward, UML can support agile development’s emphasis on working in small steps.
  • Simplifying Requirements – By combining UML with methods such as user story mapping, it is possible to reduce the amount of documentation and make it easier to see what needs to be done.
• Balancing Modeling with Agility
  • Smart Modeling – Use UML as much as required to help with communication.
  • Empowering the Team – The team will feel more empowered if they are allowed to decide how much modeling is necessary.

Use Cases of UML Diagram

In the field of documenting, designing, and visualizing software systems and processes of business, UML, also known as Unified Modeling Language, is a powerful tool for this field, as it helps in providing clear communication between technical and non-technical stakeholders. Let’s explore some of the most common and well-known examples of UML

1. UML in Software Companies
   UML is used by many software development firms for a number of purposes, such as system analysis, architectural design, and documentation.
2. Mobile and Web App Design
   When developing web and mobile applications, UML is frequently used to plan the front-end and back-end of the application.
3. Business Process Visualization
   UML can be used to map and optimize business processes in addition to software systems.
4. System Engineering and Architecture
   UML is a crucial tool in system engineering and architectural design, especially for complex, distributed systems.

Conclusion

We have explored how UML makes it easier to design complex system architectures, mobile and web applications, business processes, and software systems. Its standardized notations and diagrams facilitate the planning, communication, and visualization of system behaviors and structures. UML is still a potent tool for creating solutions that are understandable, effective, and scalable, regardless of your role as a developer, analyst, or architect.

UML Diagram – FAQs