25-Comp-B11 Advanced Software Design · Undated paper
Question 1 of 28: Design-Activity Differences Between Waterfall and Agile
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
17-Comp-B11 Advanced Software Design — National Exams, May 2019. 3 hours, closed book exam with two aid sheets 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, reuse; Pressman, Software Engineering: A Practitioner's Approach (9th ed.) — supplementary process/metrics/quality coverage; Gamma, Helm, Johnson & Vlissides (GoF), Design Patterns: Elements of Reusable Object-Oriented Software — pattern-language structure, the GoF pattern catalogue, and the "favor object composition over class inheritance" / "program to an interface, not an implementation" principles; Sebesta, Concepts of Programming Languages (12th ed.) — polymorphism, dynamic binding, visibility, encapsulation, interfaces; Bertrand Meyer, Object-Oriented Software Construction — design by contract, preconditions/postconditions/class invariants; Barbara Liskov's 1987 substitutability paper for Question 12; Stroustrup, The C++ Programming Language, for friend/access-control semantics (Question 25).
Question 12 prints “Liskpv substitution principle”, a typo in the paper; it is answered as the Liskov substitution principle.
PART I — General Principles (answer any 5 of 7)
Question 1: Design-Activity Differences Between Waterfall and Agile (Part I)
Waterfall's design activity is a single, dedicated, "big design up front" (BDUF) phase that starts only once requirements are frozen and signed off: the whole architecture, the full set of class/module designs, and the interfaces between them are elaborated and documented (formal UML diagrams, a software design specification) BEFORE any coding begins, and design is treated as essentially complete when implementation starts.
Agile's design activity is emergent and incremental instead: only enough design is done up front to start the current iteration (often on a whiteboard or as CRC cards rather than a formal SDD), the design is deliberately kept as simple as it can be for what is known NOW, and it is expected to be reshaped by refactoring as later iterations reveal new requirements or better structures. Design decisions are pushed to the "last responsible moment" rather than committed early, and the design activity never fully stops — it recurs every iteration rather than occupying one phase.
The practical consequence for design activities specifically: Waterfall's design must anticipate future changes because revising it later is expensive (it is downstream of a signed-off requirements baseline), so its designers spend more effort on up-front generality and completeness; agile's design instead relies on techniques that make CHANGE cheap after the fact — simple design, automated regression tests, and continuous refactoring — so less time is spent trying to anticipate needs that may never materialize.
