CSIS 100 UML Use Case Modeling

CSIS 100 UML Use Case Modeling

CSIS 100

CSIS 100 –UML Use Case Modeling

Background:

“The Unified Modeling Language, or UML, as it is popularly known by its TLA (three-letter acronym!), is the language that can be used to model systems and make them readable. This essentially means that UML provides the ability to capture the characteristics of a system by using notations. UML provides a wide array of simple, easy to understand notations for documenting systems based on the object-oriented design principles. These notations are called the nine diagrams of UML.”

(http://www.developer.com/design/article.php/1553851/UML-Overview.htm)

In this exercise, you will be developing the first of the UML diagrams, known as a Use-Case diagram. Before beginning this lab, be sure to read the articles and watch the videos that are in your Reading & Study folder.

In this lab, you are a Systems Analyst working for Liberty University. It is your responsibility to produce a Use Case diagram (complete with Use Case descriptions for each Use Case) for a system that will model an existing system. The system that you choose to model is your decision. Some examples are the systems that you use to apply for admission to the university, the system you use to sign up for classes, the system you use to order textbooks or another system of which you are familiar.

To construct your Use Case diagram, you will use a web-based modeling tool that is found at www.draw.io. The instructions to use this tool are as follows:

1. Open a web browser and navigate to www.draw.io. You will immediately see a screen like the one below that asks you where you want to save your files. Select “Device” from this screen.

2. The next screen prompts you to either create a new diagram or open an existing diagram. Click “Create a new diagram”.

3. This opens a new screen. Just click on the “Blank Diagram” and create a blank diagram. This opens your template screen to start diagraming.

4. Click on the down arrowhead to the left of the word “General” to collapse the General symbols

5. Then click on the arrowhead next to “UML” to open the UML symbols.

6. Drag in as many Actors and Use case symbols as you need for your Use Case Diagram.

7. When you are ready, click on the File-Save As button. The next screen prompts you to give your diagram a name and to select a template for your diagram.

a. Name your file using the convention [Your First and Last Name without spaces] followed by “UseCaseDiagram”.

b. Once you have named the file, click on the Device icon and it will open your file save as menu

Sample Use Case Diagram of and ATM

Concept: Use CaseThis is a sample of a very high-level Use case Diagram. Notice that the symbols are very simple. There are only four symbols ever used in Use Case Diagrams.

1. Stickman—These are called actors. But in system modeling, actors do not need to be people. Notice the Bank in this diagram is an Actor. The Bank is a system that interacted with the system you are modeling. Notice the naming. Actors are not specific people. They are Classes of people or entities (Bank).

2. Box—In this diagram, it is the box labeled atm:ATM. This box represents the Boundaries of the system you are modeling. Is short, this would be the application you are developing.

3. Lines or Arrows—These show the relationships between Actors and Use Cases and between Use Cases to other Use Cases.

4. Ovals—These are the Use Cases. Notice the names on the Use Cases. They are all, what we call, Verb Phrases. Refill Machine—Verb is first and noun second. This is because Use Cases are actions. Notice as week it does not say Maintenance Person Refills the Machine. That is not needed because the line from the Actor tells us that.

Again, there are no other symbols on the Use Cases. If you find yourself trying to make the diagram look pretty you will lose points. They are standard and understood by all software developers. Using other symbols might look good to you but a developed may not understand what the meaning is.

Now let’s take a look at the Use Case Description. Every Use Case in your model will require a Use Case Description. This the format of the Use Case Description you will use for this Lab. There are variations of this format in the industry, but the content is generally the same. I’m filling in this form based on the sample Use Case diagram from Above. I will be using the Withdraw Cash Use Case.

Use Case Name:	Withdraw Cash
Participating Actors:	Bank Customer; Bank
Entry Conditions:	Bank Customer is successfully Logged in to the ATM
Flow of Events:	1. Select the Withdraw Funds Option 2. Enter the amount of the withdraw 3. Wait for approval 4. Verified Funds available 5. Dispenses Cash 6. Takes Cash 7. Takes Receipt 8. Logs out of the system
Alternative Flows:	4.1. Display Insufficient Funds notice 4.2 Prints receipt 4.3 Return to step 7   8.1 Return to step 2 8.2 Enter a lower amount 8.3 Return to step 4
Exit Conditions:	Customer leaves with or without cash.

Notice the numbering of the Flow of Events (the normal process when all goes right). These are numbered steps from 1 through the end (in this case 8). But notice the numbers of the Alternative Flows (a flow that only occurs is something that does not process as normal). To accurately reflect where the alternative Flow kicks in it starts with the number of the step where the problem occurred.

So normal flow would be the funds are verified in step 4. If not the system goes to step 4.1 and follows those steps. Instead of the normal log out in step 8 the customer may choose to reenter a lower amount. If so, that would take them to Alternative Flow step 8.1.

Step numbering is another critical grading criteria.

Tasks:

1. In a three-paragraph summary, describe the system you are modeling. Save this summary in a Word document entitled [Your first name + your last name] + “_UML_Lab”.

2. Create a Use-Case diagram with a minimum of 3 actors and 5 Use Cases.

3. Include 1 “extends” relationship in your model.

4. In the same Word document as your system summary, create 5 (five) Use Case descriptions. One for each of the required Use Cases you identified.

The format of your use case descriptions should be as follows:

Use Case Name:

Participating Actors:

Flow of Events:

Alternative Flows:

Entry Conditions:

Exit Conditions:

[For a discussion and example of use case descriptions, be sure to view the articles and videos in your Reading & Study folder.]

Deliverables:

Upload your diagram (saved as an XML file) and your Word document containing your summary and use case descriptions to the assignment link by the date specified in your course schedule.

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