Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
98-Comp-B11 Advanced Software Design — National Exams, May 2015. 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 four (4) questions in Part I, any three (3) in Part II, any three (3) in Part III, any two (2) in Part IV, and any four (4) 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 16 questions actually marked (4+3+3+2+4 of 27) each count for 100/16 ≈ 6.25% of the paper. All 27 questions are answered below for completeness.
Reference texts: Sommerville, Software Engineering (10th ed., Pearson) — software processes, requirements engineering, agile methods, design principles, 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 — structural/behavioural pattern catalogue (Adapter, Bridge, Strategy, Observer, Template Method, Composite, etc.); Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, inheritance and language-level object semantics; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/invariants, the open–closed principle; Barbara Liskov's 1987 substitutability paper for Question 11; Rogers, Sharp & Preece, Interaction Design, and Nielsen, Usability Engineering, for Question 21's HMI-specific non-functional requirements.
Definition. Software reuse is building new software by incorporating existing software artifacts — components, libraries, frameworks, design patterns, generators, or even whole systems — rather than developing every part from scratch.
Benefits.
Reduced cost and time, since the reused artifact does not need to be (re)built.
Improved reliability, because a component that has already been exercised in prior use has an established track record and its defects have already been found and fixed by earlier users.
Reduced process risk, since the effort to integrate a known component is easier to estimate accurately than the effort to build new, unproven code.
Effective use of specialist effort, since reuse concentrates the cost of building a genuinely good component into a single effort, amortized across every project that reuses it.
Standards compliance, since a widely-reused component may already meet accessibility, security, or regulatory standards the new project would otherwise have to satisfy from scratch.
Challenges.
Loss of control over evolution, since a reused component's future direction (or discontinuation) is controlled by its own maintainer/vendor, not the reusing project.
Cross-boundary tool support gaps, since debugging and static analysis tools often stop being effective at the boundary of a third-party component whose internals are opaque.
"Not invented here" resistance, a cultural cost where engineers distrust or under-value externally-built code regardless of its actual quality.
The cost of building reusability itself, since a genuinely reusable, well-documented, sufficiently general component is more expensive to build than a one-off equivalent, and that extra generality is sometimes never exercised (over-engineering risk).
Imperfect fit, where a reused component almost, but not quite, matches the new requirement, forcing a costly choice between adapting the requirement to the component or adapting (forking) the component.
