25-Comp-B11 Advanced Software Design · December 2019
Question 21 of 28: Design Strategy for the Three Usability Goals
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
17-Comp-B11 Advanced Software Design — National Exams, December 2019. 3 hours, closed book exam with one aid sheet allowed (written on both sides), no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any five (5) questions in Part I, any three (3) in Part II, any four (4) in Part III, any two (2) in Part IV, and any five (5) in Part V — only the first questions answered, in each part, as they appear in the answer book are marked. All questions carry equal weight, so the 19 questions actually marked (5+3+4+2+5 of 28) each count for 100/19 ≈ 5.26% of the paper. All 28 questions are answered below for completeness.
Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, design principles, testing, dependability; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process and quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — creational/structural/behavioural pattern catalogue and the "program to an interface, not an implementation" / "favor object composition over class inheritance" principles; Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, visibility, and multiple inheritance semantics; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/class invariants; Barbara Liskov's 1987 substitutability paper for Question 12; Karl Wiegers, Software Requirements (3rd ed.); Myers, The Art of Software Testing, for Question 6.
PART I — General Principles (answer any 5 of 7)
Question 21: Design Strategy for the Three Usability Goals (Part IV)
Easy to learn. Use consistent, platform-familiar UI conventions (standard menu/toolbar placement) rather than inventing new interaction idioms; apply progressive disclosure — the everyday Add/Edit/View-balance actions are visible by default, while rarely-used options are tucked behind a secondary menu; pre-fill sensible defaults (e.g. today's date) so a first-time user has fewer decisions to make on their first transaction.
Easy to use. Minimize the number of steps for the most common task (a one-click "Quick Add Transaction" form); remember recently-used categories to speed up repeat entry; keep the View strictly separated from the Model (Question 18), so the interaction design can be iterated and usability-tested without ever having to touch the underlying business logic.
Help prevent and/or fix user errors. Validate input at entry time (disallow a negative amount where the field means "spend," offer a date picker instead of free-text date entry) so malformed data is caught immediately rather than after saving; require an explicit confirmation dialog before a destructive action such as deleting a transaction; and provide Undo/Redo built on the Command and Memento patterns (Question 20), so that even a mistake that passed validation (e.g. the wrong amount was accepted) is trivially and safely reversible rather than requiring the user to manually reconstruct the prior state.
