Question 13 of 27: Framework, Library, and Design Pattern
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.
PART I — General Principles (answer any 4 of 7)
PART III — Patterns (answer any 3 of 5)
Question 13: Framework, Library, and Design Pattern (Part III)
Library. A collection of callable functions/classes that application code invokes as it needs them — the application is in control of the overall flow and calls INTO the library for a specific service (e.g., a math library, a string-formatting library).
Framework. A reusable, semi-complete application skeleton that defines the overall control flow and architecture itself, and calls INTO application-supplied code at defined extension points (the "Hollywood Principle": don't call us, we'll call you — also known as Inversion of Control). A web framework, for example, owns the request-handling lifecycle and invokes the developer's controller methods at the right point in that lifecycle.
Design pattern. Not executable code at all — a documented, reusable SOLUTION TEMPLATE (name, problem, solution structure, consequences) to a recurring design problem, expressed as a structure of collaborating classes/objects that a developer implements by hand, afresh, every time it applies. No shared code artifact is produced or distributed; only the design IDEA is reused.
Main differences. They differ in what is reused and who controls program flow: a library reuses CODE that the application calls (application retains control); a framework reuses CODE AND architecture, and itself calls the application (framework retains control — full inversion of control); a design pattern reuses only a DESIGN SHAPE, with no shared code and no control-flow ownership at all — it can be applied inside a library, a framework, or neither.
