UML usually consists of three types of diagrams: structural, interaction, and behavioural. The activity diagram is one of the behavioural diagrams. UML activity diagrams serve a greater understanding of business ideas and help communicate with other system actions. The activity diagram portrays all the actions from the start point to the end, having all the actions, paths and decisions made by the system.
It is almost the same as a flow chart that describes all the entities present in it. However, flowcharts are used by non-programmers, whereas activity diagrams are used by professional developers, software engineers, builders, contractors and DevOps.
This guide is all about the UML activity diagram. You'll be able to learn more about activity diagrams, e.g., what they are and how they serve developers understanding a big project. What could be the useful applications of activity diagrams? Keep reading and learn more about the activity diagram.
In this article
What is an Activity Diagram?
The activity diagram is a little different from other diagrams, depicting the system's dynamic nature. Other diagrams show operations working from one object to the other, whereas the activity diagram illustrates activity from one end to the other. There is a lot of reverse and forward engineering involved in these types of diagrams, where an operator can move from one action to the other if an issue arises.
The activity diagram portrays the parallel and concurrent flow of the system. These flow charts can help engineers understand the actions that need to be done after one action. So, the activity diagram provides an edge to the engineers to execute their plans beforehand. The biggest applications for the activity diagrams are their help in software engineering and development.
What are the Activity Diagram Symbols?
There are multiple components used to create an activity diagram. Here are a few of the names and symbols of those.
Start Symbol
It is a kind of a big dot-shaped symbol used to define the starting point of the activity diagram.
Final Node/End State
It is the state in which a particular activity ends. A filled circle within the circle is used to denote the Final state. An activity diagram may also have more than one final state for a complex system.
Activity Symbol
The activity symbol is just a rectangle having its all edges folded inwards. There are short descriptions used inside the symbols to indicate the activities. These are considered the main building blocks of an activity diagram.
Connectors
These are denoted as simple lines having arrows at one end of these lines. It shows the direction of the activity in the diagram.
Joint
Joint describes two or more concurrent activities to a single one, and flow continues till the next operation.
Fork
Fork is another important part of the activity diagram, where one activity splits into two or more activities. It is simply the opposite of the joint.
Merge
When two activities don't behave concurrently, the diagram uses the merge symbol, ending in one activity irrespective of the path.
Send/Receive Signal
These symbols are used to send and receive information from one activity to the other respectively.
Note symbol
It is not as important as the other symbols in the activity diagram, as it is just used to make a note to understand something. A simple piece of information is written inside the note symbol.
Loop Symbol
A loop symbol is used when there is a need to repeat the activity or a sequence of activities. Here is how to show it in the diagram.
When to Use Activity Diagrams?
An activity diagram is a useful tool to depict, plan, and execute operations in a system. It provides an edge to the software engineers to make changes before and after execution.
The margin of error lowers when you have designed everything on the paper before execution, as you know what operations are going to be held next.
While you're in the designing phase, it gives you the liberty to check the compatibility of the software and whether it is a good fit for your model or not.
Activity diagrams let you know about the dynamic aspects of your model. It also simplifies the workflow of the system and gives a better idea if you need to make changes to it or not. The notations in the activity diagram make it different from other flowcharts and provide the clarity you need.
It is used for the maintenance engineers as a reference diagram if they are willing to make changes in the model. It is also used to check already running models if an inefficiency comes their way. Even if you're a non-technical stakeholder, an activity diagram helps you visualize a lot of complex operations running under a model.
Business modelling involves a lot of executions to run it in a better way. It could be a great tool for business owners to provide information to the new employees to understand business values.
How to Make an Activity Diagram?
Activity diagrams are different from those flowcharts. The activity itself is the biggest difference between the activity diagram and a flowchart. There needs to be a thorough understanding of the activity and the elements involved in the activity diagram. The conditions, constraints, and conditions must be checked before drawing an activity diagram.
Activity diagrams for software engineers are too crucial. They are quite vigorous in making use of the activity diagrams before performing a task. So, there need to be certain steps to draw these diagrams. The process is split into a few steps for better understanding.
Step 1: Identify the start and final state of the activity diagram.
Step 2: Identify the activities, elements, constraints, and associations between the activities.
Step 3: The mental layout of the diagram must be there before turning your ideas into paper.
Step 4: Draw the diagram with proper notations and symbols.
Step 5: Make notes for complex diagrams for better understanding for those who come to learn your model.
To create an activity diagram, you would need to choose a tool first. If you are looking for a diagram maker that is free and friendly to beginners, try EdrawMax. It has simple and clean user interface similar to MS office and offers over 10,000 free templates for you to get started.
3 Activity Diagram Examples
Here are three of the Activity diagram examples.
Activity Diagram for Library Management System
This is an activity diagram for the library management system. This diagram has six activities: inquiry, checking, validity, issuing the book, not issuing and keeping the record. There are other components and associations in this diagram as well.
This library management system diagram helps software engineer to understand and work on the system. It also helps him know the requirements for the hardware to run this model perfectly.
Activity Diagram for Online Shopping
There are a number of models used for online shopping, having different actions according to the needs of the company and buyers. Most of us tend to buy our daily life accessories through online stores. It's been a part of our lives now.
So, activity diagrams for such models are really crucial. However, as a software engineer, you might like to have fewer clicks to get your work done so that your customers don’t need to put complex details while buying from you. This activity diagram shows that you and your customers don't need to go through a lot. Just a few entries there, and you are good to go!
Activity Diagram for Bank Withdrawal
Bank withdrawals are the simplest ways to provide a simple application of an activity diagram. This activity diagram shows a cashier just needs to log into the system and ask his customers whether they want a withdrawal or a deposit. If he is after withdrawals, you must check the amount already in the bank account.
If there is enough amount present, you need to progress the payment and update the remaining balance, which is sometimes done by the system automatically due to another program running for that purpose.
Conclusion
Activity diagrams are a really important part of a system and give you a better sense of the model. If you are a software engineer, you need to learn about the activity diagrams as most of the businesses like banking, shopping and construction sites need a readymade model to follow.
These activity diagrams are useful while making changes to the system when it needs modifications. However, what bothers me the most is where to start with. Where do you need to find appropriate tools to draw your activity diagrams? There must be some ease for the engineers to kick start.
So, there are a number of platforms offering online activity diagram templates for you. If you want to make activity diagrams online without issues, Edrawmax helps you create awesome designs in no time. You will get an online template to work with and have all the tools and shapes to explore according to your needs.
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