FIT2001 Chap.5 Use Cases and Interaction Contracts

Use Cases and Interaction Contracts

Define use case

The course material gives this chapter a concrete anchor: Week 5 develops use-case diagrams and descriptions as requirements artefacts. That use case anchor controls how main success scenario is explained and how alternate flow is tested in changed practice.

Use Cases and Interaction Contracts turns use case, main success scenario and alternate flow into executable reasoning.

The chapter's practical target is to write a use case whose preconditions, main flow and alternatives support design and testing, so every explanation should connect syntax to program state, control flow and observable output.

Treat use case as a precise program object, not a loose label. Identify the value or responsibility of use case before execution, then trace what can read it, change it or depend on it.

This makes state changes visible before they become debugging guesses.

Use main success scenario to explain the program's next move. Work through one representative main success scenario input by hand and name the branch, iteration or call that follows.

If the main success scenario trace cannot be stated, the code may run by accident rather than by understood design.

Trace main success scenario

Bring in alternate flow as the test of structure.

Compare normal, boundary and invalid inputs for alternate flow; state the expected behaviour first; then use the mismatch between expectation and result to localise the defect.

For the application — write a use case whose preconditions, main flow and alternatives support design and testing — write the smallest complete example that exposes the rule.

Explain why the alternate flow result works, what would break it and how the program should signal or recover from that failure.

Before running an example involving use case, make a trace table with the important state before and after each operation. Include the value associated with use case, the control decision governed by main success scenario and the output or object affected by alternate flow.

The use case table turns an unexplained result into a sequence that can be tested one transition at a time.

Test three inputs: an ordinary case, a boundary case and an invalid case. State the expected alternate flow result for each before execution, then compare it with what the program actually does.

A useful test of main success scenario isolates one rule; changing several conditions at once cannot reveal which condition caused the failure.

Test with alternate flow

Practise explaining the solution without reading the code.

For fit2001, name the data representation, the control flow, the responsibility of each function or class and the reason the chosen design supports write a use case whose preconditions, main flow and alternatives support design and testing.

This alternate flow rehearsal matters when a written test or interview asks why the program works rather than whether it produces one correct output.

A complete response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to main success scenario, and use alternate flow to test the result.

The final sentence about alternate flow should answer the question actually asked rather than merely repeat the topic.

The controlling limit is specific: Ui clicks are not the goal and unnamed exceptions produce untestable gaps.

Keep that alternate flow limit beside the worked example, because it separates a careful fit2001 answer from one that sounds confident but claims more than the task or evidence supports.

For revision, retrieve use case, main success scenario and alternate flow without notes, explain their relationship aloud, then complete a changed version of the application: write a use case whose preconditions, main flow and alternatives support design and testing.

Record the first failed main success scenario reasoning move and repair it before attempting another case.

What this chapter covers

• 01

  use case

• 02

  main success scenario

• 03

  alternate flow

• 04

  Applying use case

• 05

  Limits of main success scenario and alternate flow

Complete a booking use case

Key terms

use case

Goal-oriented description of interactions between an actor and system under stated preconditions. This chapter uses the concept when students write a use case whose preconditions, main flow and alternatives support design and testing. Use this definition when the task is to write a use case whose preconditions, main flow and alternatives support design and testing.

main success scenario

Normal interaction sequence that achieves the use-case goal. It helps explain the reasoning required to write a use case whose preconditions, main flow and alternatives support design and testing. Use this definition when the task is to write a use case whose preconditions, main flow and alternatives support design and testing.

alternate flow

Valid deviation, exception or failure path tied to a step in the main scenario. Its limit matters because UI clicks are not the goal and unnamed exceptions produce untestable gaps. Use this definition when the task is to write a use case whose preconditions, main flow and alternatives support design and testing.

Use Cases and Interaction Contracts FAQ

Exam move

Reconstruct the relationship among use case, main success scenario and alternate flow; complete the chapter application without notes; then test the result against this limit: Ui clicks are not the goal and unnamed exceptions produce untestable gaps.

Working through Use Cases and Interaction Contracts in FIT2001? Sia is AskSia’s AI Information Technology tutor — ask any FIT2001 Use Cases and Interaction Contracts question and get a clear, step-by-step explanation grounded in how FIT2001 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.