How to Create a UML Sequence Diagram

Create New UML Sequence Diagram

To begin, launch the Software Ideas Modeler and select the option "Create New Project". Then chose the right diagram type from the Add New Diagram section on the right in the Project Properties tab. Navigate to the UML group and choose "Sequence Diagram" to get started. This diagram type is ideal for showcasing the sequence of interactions between objects, such as a user and an ATM.

Modeling the ATM Transaction Process

Adding Actor and Standard Lifelines

Adding Actors: Start by identifying the participants in the interaction. For an ATM transaction, the primary actor is the User. Select the Actor tool from the toolbox and click on the canvas to add an actor. Label the first actor as "User."
Adding Lifelines: Next, represent the ATM with a separate lifeline. Drag a lifeline from the toolbox and place it parallel to the User actor. Name it "ATM."

Modeling Interactions with Sequence Messages

Call, Reply and Self Messages

Insert Card: To add a "Call Message" from the User to the ATM, select the Call Message tool from the toolbox. Click on the User lifeline and drag your mouse to the ATM lifeline, then release. An edit box will appear where you can enter the message name, "Insert Card."
Adding the Read Card Self Message: To add a "Self Message," which indicates an action the system performs on itself, select the Self Message tool from the toolbox. Drag this tool button and drop it over the ATM lifeline's execution occurrence bar. This specifies that the ATM is reading the card as part of its internal process. An edit box appears; here, enter "Read Card" as the name of this self message.
Prompt for PIN: For a "Reply Message," indicating the ATM's response to the User, reverse the process. Select the Reply Message tool, click on the ATM lifeline's execution occurrence bar, drag to the execution occurrence bar on the User lifeline, and label it "Prompt for PIN."
Continue with "Enter PIN" as another call message, "Check PIN" as a self message and "Display Transaction Type Prompt" as a reply message, following the steps outlined above.

Incorporating Decision-Making with Fragments

In the process of modeling an ATM transaction, incorporating decision-making elements is crucial to reflect the real-world scenario accurately. Software Ideas Modeler provides a sophisticated yet straightforward way to include these elements through the use of UML Fragments.

Creating the Alt Fragment

Alt Fragment Introduction: To begin, select the "Alt Fragment" tool from the toolbox. This tool allows us to delineate areas within our diagram where alternative paths or decisions will be taken. Click and drag on the canvas to specify a big enough area to encompass five messages, which will cover the alternative scenarios of dispensing money or viewing balance.

Adding Interaction Operands: Once the alt fragment is created, we introduce interaction operands to divide the alternative paths. With the alt fragment selected, click on the "Add Interaction Operand" button in the context bar. This action allows us to add separate sections within the alt fragment for different transaction options. Add two operands to represent our scenarios: dispensing money and viewing balance.

Naming Guards: For clarity and specificity, name the guards for these operands as [Dispense money] for the first and [View balance] for the second. These labels serve as conditions that guide the flow of the transaction process based on user choices.

Adding Messages Within Alt Fragment

For Dispensing Money section:

Call Message for Selection: Start by adding a "Call Message" for the action "Select 'Dispense Money' and Specify Amount." This is done by selecting the Call Message tool, clicking on the User lifeline, and dragging to the ATM lifeline.
Reply Message for Action: Follow with a "Reply Message" titled "Dispense Specified Amount of Money," showing the ATM's response to the user's selection.
Receipt Printing: Add another "Reply Message" for "Print receipt." This action reflects the ATM offering the user a receipt for the transaction.

For Viewing Balance section:

Call Message for Balance Inquiry: Add a "Call Message" for "Select 'View Balance,'" illustrating the user requesting their account balance.
Reply Message for Displaying Balance: Include a "Reply Message" named "Display Balance," which shows the ATM providing the account balance information to the user.

Making Receipt Printing Optional

With the "Print receipt" message selected, utilize the "Create Opt Fragment" action from the context bar. This action wraps the "Print receipt" message within an Opt Fragment, indicating that printing the receipt is an optional step in the transaction process.

Looping the Transaction Process

After setting up the alt fragment to cover the transaction choices, it's time to introduce repetition for continuous user interaction. Select the alt fragment and double-click on the "Loop Fragment" tool in the toolbox. This encases the entire alt fragment within a Loop Fragment. To specify the condition for repetition, press the DOWN key to insert a new interaction operand within the loop fragment and type the guard [Until the user quits the ATM]. This condition allows the transaction process to repeat based on user input.

Finalizing The Process

To conclude the transaction sequence, add a "Return Card" reply message from the ATM to the User. This signifies the end of the transaction process and models the physical action of the ATM returning the user's card.