What is a UML diagram?

UML diagrams explained

What is a UML diagram? A UML diagram is a way to visualize systems and software using Unified Modeling Language (UML). Software engineers create UML diagrams to understand the designs, code architecture, and proposed implementation of complex software systems. UML diagrams are also used to model workflows and business processes. Coding can be a complicated process with many interrelated elements. There are often thousands of lines of programming language that can be difficult to understand at first glance. A UML diagram simplifies this information into a visual reference that’s easier to digest. It uses a standardized method for writing a system model and capturing conceptual ideas. UML diagrams help keep track of relationships and hierarchies between important lines of code. While these diagrams look similar to some decision trees or flowcharts, they have unique attributes. Simplifying something as complex as a barrage of code is extremely useful for engineers and non-technical stakeholders. It allows them to stay on top of the projects they are working on and avoid getting lost in the endless complexities inherent in software programming. UML diagrams also divide the components and subcomponents that are essential to building a piece of software.

Benefits of UML diagrams

UML diagrams are incredibly beneficial to any software development team. Here are some of the main advantages of using a UML diagram:

Makes it easier to understand complex ideas and systems

UML diagrams make abstract ideas and software systems easier to understand through visualization. This is beneficial for software engineers who need to collaborate when building software. UML diagrams also make it easier for software engineering teams to communicate with external stakeholders. Software engineers can use the UML model to explain how the system works to non-tech-savvy people.

It turns complex code into a visual diagram

Building a piece of software often requires thousands of lines of complex code, with relationships and hierarchies within them. Interpreting this code can be difficult and time-consuming. Using UML simplifies this process by turning coding environments into easy-to-understand visual diagrams.

It keeps everyone on the same page

UML works across different programming languages and development processes. It is a standardized way to visualize a system’s design. Using this universal language improves communication and understanding between a team of software engineers. If anyone on the team questions how a system works, the visual diagram acts as a point of reference. This aligns team members on the progress and task priorities within the software development process.

It allows developers to see the big picture of a system

During the software development process, it’s important to understand and remember what you’re trying to build. Developers can get bogged down when writing massive libraries of code. This can cause them to get lost in the process rather than see the project as a whole. A UML diagram helps to create an overarching, big picture of the overall system. This helps developers stay focused on the end goal.

It helps non-programmers understand the processes and functionalities of software

Software engineers are the only ones who can truly understand the functionalities, relationships, and hierarchies within a library of code. But other people in the same organization can also play an important role in the project. Product owners, managers, and stakeholders often can’t decipher the programming language used to build a piece of software. A UML diagram helps everyone outside the development team understand the programming process and how the system is meant to work.

Using a common notation means any programmer can understand it

Not all programmers understand and specialize in the same type of code and programming languages. There are hundreds of different ways to develop the same library of code. A UML diagram ensures that programmers with different skills and efficiencies can work together.

Types of UML diagrams

There are two subcategories of UML diagrams: structural diagrams and behavioral diagrams. Structural diagrams depict the components that make up a system and the relationship between those components. These diagrams show the static aspects of a system. Behavioral diagrams represent what happens within a system. They show how all the components interact with each other and with other systems or users.

Structural diagrams

Class diagram

A UML class diagram depicts a static, object-oriented system. It defines projects by classes, attributes, and functions; as such, it is a fundamental building block of any object-oriented solution. It shows the classes within a system and the operations of each one.

Package diagram

Package diagrams group classes into packages. They show the different dependencies and relationships between the packages within a system.

Object diagram

Object diagrams are similar to class diagrams in that they show the relationships between the objects in a piece of software. The difference is that object diagrams use real-world examples. Object diagrams are also called instance diagrams because they display what the system looks like at a specific moment in time.

Component diagram

A UML component diagram gives developers an overarching understanding of a system’s physical objects. This type of UML diagram shows the structural relationship between each physical component and subcomponent in a complex software system. This helps stakeholders understand how the components are organized and wired together.

Composite structure diagram

Composite structure diagrams visualize a class’s internal structure. These diagrams break down the network of classes, interfaces, and components. This type of UML diagram also shows how these elements interact with each other and why they are essential to the overarching software structure.

Deployment diagram

A deployment diagram shows the relationship between the software and hardware components in a system. It depicts the physical arrangement of the nodes in a distributed system. These diagrams are especially useful when the software being developed will operate on multiple different hardware systems.

Behavioral diagrams

Activity diagram

A UML activity diagram breaks down large processes into smaller activities. It’s used to hone in on any one component within a system. This behavioral diagram in UML offers a high-level overview of the dynamic aspects of a system.

Sequence diagram

UML sequence diagrams show how different objects relate and interact with one another in a system. This tool helps developers understand how, why, and in what order these interactions happen.

Communication diagram

UML communication diagrams are also called collaboration diagrams. They are relatively similar to sequence diagrams in that they focus on the messages passed between different objects. While sequence diagrams look at processing over time, a communication diagram creates a complete, big-picture map of your product.

Interaction overview diagram

Like activity diagrams, interaction overview diagrams visually represent the flow of activity and the sequence of those activities. The difference is that each activity in an interaction overview diagram is shown as a frame. The nodes in an interaction overview diagram represent the interactions in a system.

Timing diagram

Timing diagrams are useful for deployments, as they depict the behavior of specific objects within an explicit time frame. These diagrams are usually fairly straightforward; however, when they are dealing with more than one object, they show the interactions between many different and important sequences within that time frame.

Use case diagram

Use case diagrams provide a graphic overview of the actors involved in a software system. They help developers analyze the relationships between use cases and personas.

State machine diagram

Also known as state chart diagrams, UML state machine diagrams show the behaviors of different components in a system. You can visualize how elements act differently according to the state of the program that is being developed.

Profile diagram

Profile diagrams are one of the newer diagrams introduced by UML 2. These diagrams are rarely used and include any diagram created in a profile package.

When to use a UML diagram

UML diagrams are mainly used in the software development process and the analysis of existing software, though they are useful for visualizing any kind of complex system. Let’s look at how UML diagrams add value to two different scenarios.

Software development

Software development teams use UML diagrams to build new pieces of software and analyze and understand existing software. Before any coding or development begins, UML diagrams help the software development team visualize and plan the project. This, in turn, helps the team with prioritization and resource allocation. UML diagrams also ensure that everyone speaks the same versatile visual “language,” even when the coding used in the project isn’t universal. Having a diagram that everyone understands makes cross-company communication easier. Even those without a coding background will understand the nuances and flow of a project.

Business management

UML diagrams have become increasingly popular in business management as they help leaders organize and visualize their workforce’s workflow. These diagrams are also useful for business owners who want to improve their understanding of certain business operations’ progress. Teams can use UML to visualize the trajectory of a process and how the elements within that process will interact with each other. UML diagrams also help teams understand what’s required for a system to function properly and how it can integrate with other systems and software. Because visual information is absorbed more easily than non-visual, diagrams ensure that employees and management are on the same page, regardless of their role or experience.

UML diagram best practices

As with everything, there are certain ways to ensure that you make the most of tools like UML diagrams.

Start with a template

It can be difficult to create a useful UML diagram from scratch, especially if it’s your first time. Using pre-made diagramming templates can save you time and ensure you aren’t missing any important diagram components. It also gives you an excellent starting point that you can build on. Over time, you can adapt the template to suit your specific needs and requirements.

Understand the reason behind creating the UML diagram

A UML diagram serves a specific purpose — which is why there are so many different types. You should sit down with your development team and understand why you’re creating the UML diagram. This will help you choose the most optimal type of diagram, which will, in turn, help you achieve the best possible results.

Share and collaborate with your team

The primary purpose of a UML diagram is to increase a team’s understanding through visualization. However, visualizing isn’t the only way to improve understanding. You can also share your UML diagrams with your team to promote collaboration and ensure that everyone is on the same page. This gives all members of the team a chance to contribute, thus increasing collaboration. It also ensures that nothing gets left out and that everyone understands the information in the diagram.