25-Comp-B11 Advanced Software Design · December 2019
Question 7 of 28: Software Reuse — Importance, Activities, and the Two Directions of Reuse
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 7: Software Reuse — Importance, Activities, and the Two Directions of Reuse (Part I)
Software reuse is building new software wholly or partly from existing software artifacts (components, libraries, frameworks, patterns, or whole subsystems) instead of writing every part from scratch. It is important because it reduces development cost and time (the reused part does not need to be built), improves reliability (a widely-used component has already been exercised by many other systems), and promotes consistency across a product line.
Major activities during design and implementation: identifying candidate components against a domain/component catalogue; generalizing a component's interface (parameterizing what is specific to one use so it fits others); wrapping or adapting a component whose interface does not directly match (Question 22's composition-over-inheritance principle is the standard technique here); and verifying licensing/version compatibility before integration.
(i) Using an existing reusable component. A project adopts an existing open-source logging library (e.g. Log4j/SLF4J) instead of writing its own logging subsystem.
(ii) Producing a reusable component for others. A team designs a well-documented, generic PaymentGateway interface with a stable API, deliberately generalized beyond its first caller, so that other projects in the organization can integrate it without modification.
