Faculty of Computer & Information Use Case Diagram Faculty of Computer & Information Software Engineering Third year 2010-2011

Use Case Diagram A use case is a set of scenarios that describing an interaction between a user and a system. It displays the relationship among actors and use cases.  The two main components of a use case diagram are use cases and actors

Use Case Diagram Use Case Actor A use case describes a sequence of actions that provide something of measurable value to an actor . Actor An actor is a person, organization, or external system that plays a role in one or more interactions with your system A document describing the use case in details

Identifying Use Cases Which functions does the actor require from system? Does the actor need to read, create, destroy, modify, or store some kind of information in the system? Does the actor have to be notified about events in the system

Identifying actors Useful questions Who will use the main functionality of the system(primary actors)? Who will need to maintain, administrate, and keep the system working (secondary actors)? With which other systems does the system need to interact? Who or what has an interest in the results (the value) that the system produces?

Use Case Examples

Use Case Examples

Creating Use Case Diagrams Start by listing a sequence of steps a user might take in order to complete an action.  For example a user placing an order with a sales company might follow these steps.  Browse catalog and select items. Call sales representative. Supply shipping information. Supply payment information. Receive conformation number from salesperson.

Creating Use Case Diagrams Associations

Example Students are enrolling in courses with the potential help of registrars. Professors input the marks students earn on assignments registrars authorize the distribution of transcripts (report cards) to students

University Information System Input Marks Enter in Course Selected Courses Student Professor Registrar

Structure of a Use Case Specification Name Actors Trigger Preconditions Post conditions Success Scenario Alternatives flows

Triggers What starts the use-case? Examples: Customer reports a claim Customer inserts card System clock is 10:00

Preconditions What the system needs to be true before running the use-case. Examples User account exists User has enough money in her account There is enough disk space

Post-Conditions A post-condition is the outcome of the use-case. Examples Money was transferred to the user account User is logged in The file is saved to the hard-disk

Success Scenario The success scenario is the main story-line of the use-case It is written under the assumption that everything is okay, no errors or problems occur, and it leads directly to the desired outcome of the use-case It is composed of a sequence of action steps Introduction | Diagrams | Writing | Linking | Guidelines

Success Scenario User enters product name, SKU and description System validates product SKU System adds the product to the DB and shows a confirmation message Introduction | Diagrams | Writing | Linking | Guidelines

Success Scenario Example User enters a keyword System presents a set of search results, and sponsored products, all of which include name, short description and price User selects a product System displays a product page, including product information, reviews and related products User adds the product to the shopping cart Introduction | Diagrams | Writing | Linking | Guidelines

Reuse Opportunities There are some types of relationships between use cases Extends Includes

Inclusion

Extension

How to make use case diagram Make interviews with user or make site view. From these interviews we can know actors and an overview of the use cases in the system. Making more and more interviews allow you to know the details about use cases or another use cases

Example

Bank System A bank has several automated teller machines (ATMs), which are geographically distributed and connected via a wide area network to a central server. Each ATM machine has a Card reader Cash dispenser keyboard/display Receipt printer. By using the ATM machine, a customer can Withdraw cash from either a checking or savings account Query the balance of an account Transfer funds from one account to another.

Bank System An ATM operator may start up and close down the ATM to replenish the ATM cash dispenser and for routine maintenance. It is assumed that functionally to open and close accounts and to create, update, and delete customer and debit card records is provided by an existing system and is not part of this problem.

ATM: Use Case Model