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What is a UML Diagram? - An Easy and Comprehensive Guide

Simply read this comprehensive guide for all the key aspects (basic concepts, usages, benefits, types, how-to-create etc.) of knowing about the UML diagram with free download UML diagram templates.

Contents

What is a UML Diagram?

A UML diagram shows the unified visual presentation of the UML (Unified Modeling Language) system with the aim to let developers or business owners better understand, analyze and undertake the structure and behaviors of their system. To be more simple, such diagram is very similar to blueprints used in construction building projects. So far, the UML diagram has become one of the most common business process modeling tools and is doing well for large and complex projects. UML is also highly significant to the development of object-oriented software with more clear and easy notations.

UML diagram examples

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Why Use UML Diagrams?

UML diagramming has many benefits for both software developers and businessman, and the most key advantages are:

UML Diagram Key Usages

The diagram can be used in many different fields including software engineering or business processes to strengthen efficiency.

What are the Types of UML Diagrams?

The two most main categories of UML diagrams are the Structure UML diagram and the Behavior UML diagram. Furthermore, 13 sub-types of UML diagrams are divided into these two groups and each one of them has a different purpose. Now let's check out all of them in more details as shown below. You can also click on them to see more and download these examples for free.

Structure Diagrams

These diagrams show different objects and the static structure of the system. The elements in a structure diagram may include abstract and some other related implementation concepts. This category has six sub-types:

Class Diagram

It is the most widely used UML diagram sub-category. The Class diagram is the building block of all object-oriented software systems. Users can depict the static structure and identify classes relationship of a system by checking system's classes and attributes. Each class has three basic elements: the class name at the top, the class attributes in the middle, and the class behaviors at the bottom. In reality, you can create classes such as "Sales Account" or "Online User" in business systems, or "Teacher" and "Student" in academic systems.

simple class uml diagram template

Composite Structure Diagram

Composite structure diagrams are used to show the internal structure, the behaviors of classifiers, and the relationships between classes in a system. The composite structure type is similar to Class diagrams but the former ones represent more detailed individual parts rather than the whole system structure. Object Diagram

Object diagrams can be considered as the screenshot of the instances and their internal relationships in a specific system. By using such diagrams, developers can be able to analyze the operations of the system at a particular instant, and check their abstract structure. Furthermore, the relationship between a Class and an Object in software development can be described as the relationship between, for example, the class "Food" and the brand "KFC" or the general class "User" and a specific username called "David" or what else.

Component Diagram

Component diagrams are used to show in what way the physical components in a system is organized. Normally, developers use the Component Diagram to check out implementation details, break down the system into smaller parts, depict the structural relationship between system elements especially in the case of large-scale complex projects with more advanced technologies.

component UML diagram example

Deployment Diagram

Deployment diagrams are generally used to show users the visual relationship between software and hardware. A sample Deployment diagram in the software development field has two main parts: Nodes (basically different kinds of servers) and Artifacts (normally client or database schema). Nodes host the Artifacts, while different types of Artifacts operate on Nodes.

deployment UML diagram example

Package Diagram

In general, Package diagrams are used to depict how packages and their elements are organized into meaningful groups in a system. More specifically, Package diagrams can be considered as a structure that includes many deployment diagrams with nodes and artifacts. So far, package diagrams are used to organize the Class and Use Case diagrams.

package UML diagram template

Behavior Diagrams

These diagrams display the dynamic behaviors or in other words, what should happen in a system. For example, the way that objects interact with each other, or a set of changes to the system over a certain period. This category has seven sub-types:

 

State Machine Diagrams (State Machines or State-chart Diagrams)

Such UML diagrams are used to represent the condition of the system, the dynamic action (different states) of a class in response to a particular time based on internal or external factors. A real-life example of the State Machine diagram could be playing Poker cards. The final result (different states) of the game can be different based on players' specific strategies.

state machine UML diagram example

Activity Diagrams

Activity diagrams are used to illustrate the interconnected flow of different activities and actions (both in sequential form or in parallel type) in a system, and to display the steps involved in the execution of a use case. This type of UML diagram is widely used both in business modeling process and software development.

Activity UML diagram example

Use Case Diagrams

A Use Case diagram can be regarded as a good starting point for discussing project key actors and processes without going into too many implementation details. This UML diagrams is also the most popular type of the Behavioral UML diagram category, and is used to analyze the functionality (the use cases) and the interactions with different types of agents (actors) of a system. For business cases, enterprises may use such diagrams to check out the customer order system by monitoring the stock, product quality and so on. For daily life cases, Use Case diagrams are similar to the Hot Sale product list of your local supermarket. You know the product name and its prices according to the list when making your purchasing decision.

management system use case uml diagram

Sequence Diagram

A sequence diagram generally shows the interaction between objects in a sequential order. It is for users to document and understand requirements in a new system. In software development, this type of diagram is used to represent the architecture of a system.

website sequence uml diagram example

Communication Diagram (Collaboration Diagram)

A Communication diagram is used to display sequenced communications between objects with the focus on primary objects and their relationships. Communication diagrams usually use number schemes and pointing arrows to show message flow. Moreover, compared with sequence diagrams, communication diagrams are much easier to be designed, but contains fewer details when drafting documentation for systems.

communication uml diagram example

Timing Diagram

A Timing diagram is a special form of the Sequence diagram that is used to show the behavior of objects over a certain time constraint. It is similar to the form of, for example, the history of iPhone development, or the growing trend of an international enterprise.

Interaction Overview Diagram

An Interaction Overview diagram displays a sequence of behaviors and helps users simplify complex interactions (rectangular frames) into simpler forms in a system. It can be considered as a mixture of specialized activity and sequence diagrams, but Interaction Overview diagrams have more elements than Activity diagrams such as interaction, time constraint and more.

More Free UML Diagram Templates

Here are more templates of UML diagrams for you to easily understand all of these UML sub-categories. All of these are editable with the free download UML diagram software. Feel free to click on any of them to see more details.

student management use case example uml sequence diagram template bank system uml diagram
Student Management Use Case Diagram UML Sequence Diagram Template Bank System Use Case Template
uml component diagram template ticket uml collabration template deployment chart template
UML Component Diagram Template Ticket UML Collaboration Template Deployment Chart Template

UML Diagram Symbols

There are many UML diagram symbols in each of the UML categories. Among all of these symbols, the Class diagrams symbols (defining attributes and operations of classes), the Activity diagram symbols (used to show states and activities) and the Use case diagram symbols (shown with different types of arrows) are the most popular ones.

uml diagram symbols

uml diagram symbols

How to Create a UML Diagram Easily?

Simply follow these steps to quickly create a professional-looking UML diagram.

1. Open a preset UML diagram template or a blank drawing page for your work. Double-click one of the icons in the UML Model Diagram category to start creating.

open uml preset templates

2. Drag and drop UML standard shapes from the built-in libraries. Adjust the shape size to fit the drawing board.

drag and drop uml symbols

3. Align or group UML shapes for the appropriate locations.

align uml shapes

4. Connect UML shapes by adding more connection points on the shapes or by using the preset relationship lines.

connect uml shapes

5. Double-click to edit default shape text.

edit uml shape text

6. Further format your UML diagram by changing the colors of shapes/lines, trying different diagram theme and adding background etc.

change uml diagram theme

7. Print, save to built-in personal/team cloud, or export to different formats including Visio, MS Office, PDF and more.

export uml diagrams

Create Your Own UML Diagrams Right Now!

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Read More:

How to Create a UML State Chart?

UML Model Symbols Guide

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