UML Diagram: Everything You Need to Know

If you’ve ever needed to map out information, you’ve likely used either a concept map or a mind map. These structures are good at creating thought models and are relatively basic to use. What happens, then, if you want to create a more complex diagram that explains how an entire process functions? In this scenario, you’d most likely be pointed towards a UML diagram. This article will define UML diagrams and walk through how you can best use them.

What Is a UML Diagram?

The UML diagram is a template based on the UML (Unified Modeling Language) that helps users visualize processes and sequences. It visually represents a system and its main actors, roles, actions, and artifacts. A UML diagram aims to enhance understanding and alter, maintain, or document system information.

What Does UML Mean?

The acronym UML stands for Unified Modeling Language. To put it simply, UML represents a modern approach to modeling and documenting software. It’s one of the most popular methods for visualizing a software program, and this visualization is demonstrated perfectly with the UML diagram.

Based on diagrammatic representations, it shows the software components. When we use visual representations, we can better understand opportunities for improvement in software development.

UML was not always a thing, but its creation resulted from the chaos around software development and documentation in the late 1990s. There were many ways to describe and represent existing software systems. Because of this confusion, there was a need to develop a better way of visualizing those systems. As a result, three software engineers at Rational Software developed the UML between 1994 and 1996. In 1997, it was adopted as the standard documenting language for visualizing a software program.

UML Diagram Use Cases

It initially gained popularity as a general-purpose modeling language in software engineering. However, it now finds its way into the documentation of various business processes or workflows. 

Flowcharts, for example, can be replaced with activity diagrams, a type of UML diagram. They provide standardized documentation for modeling workflows and more features, improving readability and efficiency.

As for how UML is used in software development and business process documentation, here are some examples:


UML diagram, in this case, is used to visualize different aspects and characteristics of the system under development. However, this is only a birds-eye view of the system and is unlikely to contain all the details required to execute the project.


UML diagrams serve as a complete design that requires implementation, often using CASE tools. However, the main drawback of using CASE (Computer-Aided Software Engineering) devices is that they need training for users, a certain level of expertise, and management and staff commitment.

Pseudo Programming Language

With the right tools, UML can function as a pseudo-programming language. However, it is not a stand-alone programming language like Java, C++, or Python. It’s necessary to document the entire system with different UML diagrams, and with the right software, the diagrams can directly be translated into code. 

Different Types of UML Diagrams

Various types of UML diagrams exist, and each serves a specific purpose. As the name suggests, some diagrams try to analyze and depict the structure of a process or system. In contrast, others describe the system’s behavior, actors, and building components. These templates can be broadly divided into behavioral and structural UML diagrams. The different types of UML diagrams can be categorized as follows:

Behavioral UML Diagrams

  • Activity Diagram
  • Use Case Diagram
  • Interaction Overview Diagram
  • Timing Diagram
  • State Machine Diagram
  • Communication Diagram
  • Sequence Diagram

Structural UML Diagrams

  • Class Diagram
  • Object Diagram
  • Component Diagram
  • Composite Structure Diagram
  • Deployment Diagram
  • Package Diagram
  • Profile Diagram

There are 14 different UML diagrams, but software developers do not use all 14 regularly to document systems and architecture. The most commonly used UML diagrams in software development are the Use Case diagram, Class diagram, and Sequence diagram.

Activity Diagram

The most important UML diagram used for business process modeling is the activity diagram. In software development, this represents the flow of different activities and actions. These can both be sequential and parallel. They provide insight into how an action is used, finished, produced, and its relationship to other activities. These are all essential components of business process modeling.

Use Case Diagram

As the cornerstone of the system, functional requirements make the system work. Use case UML diagram describes the system’s high-level requirements and how they are expressed through different use cases. This UML diagram has three main components:

  • Functional requirements
  • Actors
  • Relationships

 Interaction Overview Diagram

The interaction overview UML diagram is likely to be one of the most complex ones. We have already discussed what an activity diagram is. Additionally, we have a subset made of four diagrams, called Interaction Diagrams:

  • Interaction Overview Diagram
  • Timing Diagram
  • Sequence Diagram
  • Communication Diagram

Essentially, an interaction overview diagram is an activity diagram consisting of different interaction diagrams. You could say it combines activity diagrams and interaction diagrams. However, most websites refer to them as specialized activity diagrams. Therefore, you can use most annotations that you would typically use within an activity diagram.

Timing Diagram

Timing UML diagram visualizes the interactions of objects when the center of attention is time. We do not care about how the objects change or interact but rather how they behave in relation to a linear time axis. 

A lifeline represents each participant, consisting of a line defining stages over time as the participant progresses from one stage to another. However, the main focus of this approach is on the duration of events and the changes that take place based on the duration constraints. This UML diagram has five main components:

  • Lifeline
  • State timeline
  • Duration constraint
  • Time constraint
  • Destruction occurrence

Sequence Diagram

In recent years, sequence diagramming has gained popularity among the computer science community and as design-level representations for business application development. 

Sequence diagrams show the order in which messages and interactions happen between actors and objects. Actors or objects are only active when needed or when another object wants to communicate with them. However, all communications are represented chronologically.

Communication Diagram

Communication diagrams were formerly called collaborative diagrams in UML 1.0. As the name suggests, communication diagrams concentrate on communicating between objects.

As the core components are the messages they exchange, we can construct communication diagrams in the same way we construct sequence diagrams. The only difference is that the objects are connected by associations in communication diagrams.

Visually speaking, they differ because sequence diagrams follow a vertical structure and the message flow follows a top-down chronological approach. On the other hand, communication UML diagrams use arrows and number schemes to show messages.

The sequence diagram is probably the better choice if you choose between the two when describing a process or system. The UML documentation offers a lot of annotations that make sequence diagrams more appealing to software engineers. This is partially due to its more linear structure and partly because they have received more attention for their annotating aspects.

In contrast, communication diagrams are much easier to design because you can add an object anywhere on the board. After all, for objects to be connected, all they must have in common is their number without physically being close to each other.

State Machine Diagram

The state machine UML diagram, also known as the statecharts diagram, depicts the various states of an object within a system. As the name implies, a state machine diagram is essentially a machine that describes the different states of an object based on internal and external events.

A straightforward example of a state machine diagram would be a chess game. A typical chess game has white making moves and black making moves. However, it doesn’t matter whether it is either team’s turn, as the game can end with a checkmate, resignation, or draw. Imagine these as the different states of the machine.

Class Diagram

The class diagram is the most common type of UML diagram. Software developers mainly use this diagram for software documentation since they construct most software based on an object-oriented paradigm. Therefore, using class diagrams to document the software makes sense. This is because OOP is based on classes and the relationships between them.

The class diagram consists of classes, along with their attributes (also known as data fields) and their behaviors (also known as member functions). Each class has three fields: the class name above, the class attributes directly below, and the class operations/behaviors below. This relationship between different classes is what defines a class diagram.

Object Diagram

As we discuss structural diagrams, we must unearth the underlying concepts of computer science-related concepts. Software development considers classes to be abstract data types and objects to be instances of the classes. Suppose we have a class “car” that is an abstract type. An instance of that class is an “Audi.” Highlighting the objects within a given class is the goal of an object diagram

This UML diagram makes it easier for software developers to determine if the abstract structures they have created (class diagram) will represent a viable structure when put into practice. Some software developers view it as a secondary accuracy check.

Component Diagram

A component diagram can help break down a complex system into smaller parts. Sometimes, it can be challenging to represent a system’s architecture since it might span multiple departments or use different technologies. Component diagrams seek to break this up into distinct sections to understand each individually and in relation to the overall structure.

Composite Structure Diagram

As its function is very specific, this type of UML diagram is not commonly used. A composite structure diagram actually represents the internal structure of a class and the relations between different class components.

Generally, business professionals do not express their interest in composite structure UML diagrams since they mainly focus on the top-level view of components and the communication with one another. As a manager, there is no need to know how a specific class data member is related to another member of a different class. That is why the usage of a composite structure diagram is infrequent.

Deployment Diagram

Software developers use deployment diagrams to visualize the interrelationship between software and hardware components. Specifically, they provide a visual representation of installation processes of software components on hardware components.

A common deployment diagram for a web application should include:

  • Nodes
  • Artifacts

Hence, the nodes host the artifacts. The database schema resides on the database server, and the application client resides on the application server. As the name suggests, the deployment diagram indicates specifically where each software component resides.

Package Diagram

As we discussed above, the package diagram serves as a container for deployment UML diagrams. It contains nodes and artifacts. Different packages include nodes and artifacts in the same way that a namespace contains a set of interconnecting names. They organize models and components into groups.

The ultimate purpose of a package diagram is to demonstrate the relationships among the large components that make up a complex system. Nowadays, programmers find this abstraction opportunity an excellent reason to utilize package diagrams, especially when there are some unnecessary details involved. However, it is possible to construct a package from several other packages to depict more complex systems and behaviors.

Profile Diagram

Profile diagrams are not typical UML diagram types. They can be seen as more of an extensibility mechanism rather than a diagram type like any other.

In UML notations, stereotypes, tagged values, and constraints let you extend or customize existing notations. Profile diagrams are like a language. If you speak English, you can create new sentences, and if you know profile diagrams very well, then you can create new propositions.


Over the past few years, UML diagrams have become a much more powerful tool for documenting various business processes or workflows. Initially, only software developers and professionals from the IT sector used UML, but nowadays, many people use UML diagrams in their daily work and have adopted them across different industries. If you liked this article and want to learn more about Fresco, stay tuned to our blog to learn more.



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