SEEM 3430 TUTORIAL USE CASE TUTORIALseem3430/Tutorial Notes/use case tutorial.pdf · USE CASE TUTORIAL SEEM 3430 TUTORIAL. ... numbered series of steps – the key differentiator

USE CASE TUTORIAL

SEEM 3430 TUTORIAL

OUTLINES

▸ What is use case?

▸ Formal Use Case

▸ Informal Use Case

▸ How to build Use Cases

▸ Use Case Diagram

WHAT IS USE CASE

WHAT IS USE CASE

WHAT IS USE CASE

▸ A use case represents how a system interacts with its environment by illustrating the activities that are performed by the users and the system’s responses.

WHAT IS USE CASE

WHAT IS USE CASE

▸ A use case represents how a system interacts with its environment by illustrating the activities that are performed by the users and the system’s responses.

WHAT IS USE CASE

Use cases are a means of expressing user requirements.

Use cases are used extensively in the analysis phase.

WHAT IS USE CASE

MORE ABOUT USE CASE…

▸ Sequence of actions that provide a measurable value to an Actor.

▸ Describes a way in which a real-world Actor interacts with the system.

▸ Include high-level implementation decisions.

▸ Can be written in both an informal manner and a formal manner

▸ Depicted as Ellipses in Diagrams

FORMAL USE CASE

FORMAL USE CASE

▸ The formal, or classic use case, is a tool used to gather structured information about how users will use the software.

▸ Formal use cases are gathered in a template, which structures the information.

▸ While this structure can vary from company to company, or even project to project, there are a few common and critical sections to the structure.

▸ The two main benefits of having the structure are that it helps with thoroughness (much harder to leave a field blank than it is to forget about it), and it helps with scanning by readers of the document.

FORMAL USE CASE

SOME COMMON ELEMENTS IN A USE CASE

▸ Actor – The person or people who will perform the steps of this use case.

▸ Preconditions – A description of the relevant and non-trivial state(s) of the system prior to the use case starting.

▸ Normal course – A description of the use case itself. This description can either be in narrative form, or a numbered list (1..N) of specific user steps. When a use case (such as “User approves/rejects customer requests”) has more than one way that a user can accomplish the needed steps, the most common way is shown here – only a single path is shown.

▸ Assumptions – Any assumptions that are implicit in the definition of the use case.

FORMAL USE CASE

SOME COMMON ELEMENTS IN A USE CASE

▸ Alternate courses – Descriptions of alternatives to, or deviations from the normal course. For example, the most common course might be to view the oldest unaddressed customer requests. An alternate course may be to view the unaddressed requests from the largest customers.

▸ Exception courses – Descriptions of what the user will experience when something goes wrong.

▸ Post-conditions – Description of the affected portions of the state of the system after the use case has completed.

▸ Frequency of use – An estimate of how often a particular use case will be exercised.

FORMAL USE CASE

ADVANTAGE

▸ Detailed information about use cases, making it easy to estimate the cost of implementation.

▸ Thorough coverage of the use cases is influenced by the use of a template.

▸ Easy for readers to absorb. The structure of the document makes scanning easy, and also helps targeted lookups when a reader needs a specific piece of information.

▸ Consistency with other use cases is much easier to assure when using a template.

FORMAL USE CASE

DISADVANTAGE

▸ Expensive to maintain. Mapping a “use case” to the template requires some effort. Since formal use cases contain more (explicit) information than other use cases, there is more content to document, validate and modify. More content equals more cost (of maintenance).

INFORMAL USE CASE

INFORMAL USE CASE

▸ The informal use case is the tool of the Agile Requirements Manager. It is a paragraph describing the user’s goals and steps. Also referred to as a basic use case.

▸ Note that the paragraph format can also be replaced by a numbered series of steps – the key differentiator of this form relative to a formal use case is the lack of structured fields for “everything else” about a use case (preconditions, assumptions, etc).

▸ Name: Enroll in Seminar

▸ Identifier: UC 17

▸ Basic Course of Action:

▸ • Student inputs her name and student number

▸ • System verifies the student is eligible to enroll in seminars. If not eligible then the student is informed and use case ends.

▸ • System displays list of available seminars.

▸ • Student chooses a seminar or decides not to enroll at all.

▸ • System validates the student is eligible to enroll in the chosen seminar. If not eligible, the student is asked to choose another.

▸ • System validates the seminar fits into the student's schedule.

▸ • System calculates and displays fees

▸ • Student verifies the cost and either indicates she wants to enroll or not.

▸ • System enrolls the student in the seminar and bills them for it.

▸ • The system prints enrollment receipt.

INFORMAL USE CASE EXAMPLES - DETAIL

INFORMAL USE CASE

▸ Enroll in Seminar

▸ • Student chooses a seminar to enroll in

▸ • System checks that the student can enroll in the seminar

▸ • System calculates fees

▸ • Student pays fees and is enrolled

INFORMAL USE CASE EXAMPLES - HIGH LEVEL

INFORMAL USE CASE

▸ The player has all the tradable cells in a color group and wants to buy a house for the color group. The player has enough money to buy the house and is shown the number of houses own in that group [S1], and purchases the house. The player’s status is displayed [UC13].

▸ The player has all the tradable cells in a color group and wants to buy a house for the color group. The player does not have enough money to buy the house. The player’s status is displayed [UC13].

INFORMAL USE CASE EXAMPLES - FREE TEXT

INFORMAL USE CASE

INFORMAL USE CASE

ADVANTAGE

▸ ▪ Easy to create – quick development, iteration, and collaboration. This enables a rapid approach to documenting use cases, and minimizes the cost of developing the use cases.

▸ ▪ When done correctly, yields the most bang for the buck of any use case approach.

DISADVANTAGE

▸ Challenging to be rigorous – the short format makes it difficult to capture all the relevant information (and difficult to avoid capturing irrelevant information).

▸ Lack of consistent structure – can be transition from use case to use case, since the format is free-form

▸ Capturing the right level of content for your team can be tricky.

INFORMAL USE CASE

TIPS FOR BUILDING USE CASES


Activities Typical Questions Asked

Start a use case form for each use caseIf more than nine, group into packages

Ask who, what, and where about the tasks and their inputs and outputs:What are the major tasks performed?What triggers this task? What tells you to perform this task?What information/forms/reports do you need to perform this task?Who gives you these information/forms/reports?What information/forms/reports does this produce and where do they go?

Identify the major use cases



Identify the major steps within each use case


For each use case, fill in the major steps needed to process the inputs and produce the outputs

Ask how about each use case:How do you produce this report?How do you change the information on the report?How do you process forms?What tools do you use to do this step (e.g., on paper, by email, by phone)?

TIPS FOR BUILD USE CASES


Identify elements within steps


For each step, identify its triggers and its inputs and outputs

Ask how about each stepHow does the person know when to perform this step?What forms/reports/data does this step produce?What forms/reports/data does this step need?What happens when this form/report/data is not available?



Confirm the use case


For each use case, validate that it is correct and complete

Ask the user to execute the process using the written steps in the use case – that is, have the user role-play the use case


MORE TIPS ABOUT WRITING

▸ 1. Based on a goal.

▸ A use case describes how an actor uses the system to achieve a goal.

▸ 2. Complete or not complete.

▸ When an actor has performed the steps in a use case, the goal should be either 100% complete or 0% complete.

▸ 3. One person, one place, one time, one event.

▸ Try to write use cases that describe how one actor responds to one event in one place at one time.

▸ 4. Six to ten steps.

▸ Try to keep the main success scenario (aka primary flow) of a use case between six and ten steps. Use cases should make requirements easier to comprehend.

DIAGRAM

USE CASE DIAGRAM

▸ A use case diagram at its simplest is a representation of a user's interaction with the system and depicting the specifications of a use case.

▸ A use case diagram can portray the different types of users of a system and the various ways that they interact with the system.

▸ A use case diagram summarizes all of the use cases (for the part of the system being modeled) together in one picture

▸ Typically, the use case diagram is drawn early on in the SDLC.

DIAGRAM

ELEMENTS OF A USE CASE DIAGRAM

DIAGRAM

RELATIONSHIPS IN USE CASE DIAGRAM

▸ You can now model the interactions between the users and the system by creating the relationships between the actors and the use cases.

▸ 1. Association

▸ 2. Include (Use)

▸ 3. Extend

▸ 4. Generalization

DIAGRAM



▸ 1. Association


▸ 3. Extend


DIAGRAM



▸ 1. Association


▸ 3. Extend


DIAGRAM



▸ 1. Association


▸ 3. Extend


SUMMARY

SUMMARY

▸ Use cases contain all the information needed for process modeling, but are easier for users to comprehend

▸ A use case contains all the information needed to build one part of a process model, expressed in an informal, simple way.

SUMMARY

TAKE AWAY MESSAGE

▸ When writing a use case,- identify the triggering event,- develop a list of the major steps,- identify the input(s) and output(s) for every step, - have the users role-play the use case to verify.

QUESTIONS

QUESTIONS

▸ Questions?

Documents

SEEM 3430 TUTORIAL USE CASE TUTORIALseem3430/Tutorial Notes/use case tutorial.pdf · USE CASE TUTORIAL SEEM 3430 TUTORIAL. ... numbered series of steps – the key differentiator