Question 21 of 25: Non-Functional Requirements for Human-Machine Interfaces
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
98-Comp-B11 Advanced Software Design — National Exams, May 2014. 3 hours, open book, no calculator permitted. The paper is organized into five parts, and candidates were instructed to answer any three (3) questions in Part I, any four (4) in Part II, any three (3) in Part III, any one (1) in Part IV, and any one (1) 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 12 questions actually marked (3+4+3+1+1 of 25) each count for 100/12 ≈ 8.3% of the paper. All 25 questions are answered below for completeness.
Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, agile methods, design principles; 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 — structural/behavioural pattern catalogue (Proxy, Bridge, Strategy, Observer, Template Method, Composite, etc.); Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, inheritance and language-level object semantics (also underpins the Java/C++ discussion in Part V). Bertrand Meyer's Object-Oriented Software Construction is cited by name where the paper's own vocabulary (design by contract, open–closed principle) originates there; Barbara Liskov's 1987 substitutability paper is likewise cited by name for Question 11.
PART I — General Principles (answer any 3 of 5)
Question 21: Non-Functional Requirements for Human-Machine Interfaces (Part IV)
The printed stem reads “Site”, evidently a typo for “Cite” (or “State”); either reading asks the same thing — name three HMI-specific NFRs, then define, illustrate, and give a design strategy for each.
Usability/learnability. A new or occasional user must be able to accomplish a defined task within a stated time/error budget without prior training (Question 4's quantification pattern applied to the HMI). Example: "a new user shall complete a standard order-entry task within 5 minutes with no more than one recoverable error." Design strategy: consistent, platform-standard widget conventions plus progressive disclosure (surface common actions prominently, hide advanced options behind a secondary menu) and contextual tooltips, validated through usability testing with representative users.
Responsiveness (perceived). Distinct from the raw system response-time NFR of Question 18: the interface must provide feedback within a bounded, perceptible time even when the underlying operation itself takes longer — e.g., feedback within roughly 100 ms is perceived as instantaneous, per standard HCI response-time guidelines. Design strategy: asynchronous processing with an immediate acknowledgement (a spinner or progress indicator) that decouples perceived UI responsiveness from actual backend operation latency, rather than blocking the UI thread until the operation completes.
Accessibility. The interface must remain usable by users with visual, motor, or hearing impairments — e.g., a stated WCAG conformance level and full keyboard-only operability. Design strategy: complete keyboard navigability (no interaction possible only via mouse), screen-reader-compatible semantic markup/ARIA labelling, and sufficient colour contrast with resizable text, validated against WCAG 2.1 AA success criteria.
