25-Comp-B11 Advanced Software Design · December 2014
Question 2 of 26: Functional and Non-Functional Requirements
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
98-Comp-B11 Advanced Software Design — National Exams, December 2014. 3 hours, closed 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 four (4) in Part III, any two (2) in Part IV, and any two (2) 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 15 questions actually marked (3+4+4+2+2 of 26) each count for 100/15 ≈ 6.7% of the paper. All 26 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); Brown, Malveau, McCormick & Mowbray, AntiPatterns: Refactoring Software, Architectures, and Projects in Crisis — anti-pattern catalogue (Question 18). 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 2: Functional and Non-Functional Requirements (Part I)
A functional requirement (FR) is a statement of a service the system must provide, or of how the system must behave in response to particular inputs — it describes something the system does. Example: "The system shall allow a registered user to search for a book by ISBN and display the title, author, and current availability."
(b) Non-Functional Requirement
A non-functional requirement (NFR) is a constraint on the services the system offers, or on the system as a whole, rather than a service in its own right — it constrains how well, how fast, how securely, or under what conditions functions must operate. Example: "The search function shall return results within 2 seconds for 95% of queries when up to 200 users are searching concurrently," or "The system shall be available at least 99.9% of the time, measured over a rolling 30-day window."
A Client Request That Is Neither
Example: "The system must be built using our in-house Java/Spring framework and must be delivered within six months for $150,000." This is a project/implementation constraint, not a product requirement at all — it says nothing about a service the system performs (not a FR) and nothing about a quality attribute of that service's behaviour (not a NFR). It instead restricts the SOLUTION SPACE (which technology may be used) and the PROJECT itself (budget, schedule), both of which sit outside the requirements-engineering categories the question asks about; Sommerville classifies statements like this as project or process constraints, distinct from product requirements. A second common example is a pure business policy statement with no testable system behaviour attached at all, e.g. "the company prefers to keep this feature in-house rather than outsourced" — a management decision, not a requirement on the software.
An important asymmetry between FR and NFR: failing a single functional requirement typically makes one feature unavailable, but failing a pervasive non-functional requirement (unacceptable response time, unacceptable security) can make an otherwise functionally complete system unusable or unacceptable outright — which is why NFRs, though fewer in number, often dominate acceptance testing and architectural decision-making (elaborated further in Question 4).
