Which design methodology uses existing programming libraries and APIs to design a system or application?

• A. Bottom-Up Design
• B. Top-Down Design
• C. Incremental Design
• D. Waterfall Design

Answer: (A)

Starting with existing libraries and APIs and building the system by connecting these ready-made components is bottom-up design. This approach centers on reusing proven building blocks—data access libraries, networking APIs, UI frameworks, authentication services, and so on—and composing them to form higher-level functionality. You identify suitable components, ensure they have compatible interfaces, and then glue them together to create the complete application, expanding by adding more components as needed. This contrasts with approaches that begin by outlining the entire system and then breaking it down into parts (top-down), or developing in small, incremental steps, or following a linear, sequential process (waterfall). So using libraries and APIs to assemble the system is characteristic of bottom-up design.