CSS CS Optional — Paper-I, Section-B, Topic V.

🔑 Architectural Styles (name + justify)

• Layered — each layer uses only the layer below it (e.g. OS layers, network stacks).
• Client-server — servers provide services, clients consume.
• Pipe-and-filter — data flows through independent "filters" via "pipes."
• Repository — components read/write a shared central data store.
• MVC — Model (data) / View (presentation) / Controller (logic).

🔥 3-Tier Web Application Architecture (FPSC's favorite — asked verbatim twice)

• Presentation tier — browser/UI, what user sees.
• Application (logic) tier — business rules, server-side processing.
• Data tier — database + data-access logic.
• Why: each tier develops/scales/replaces independently (e.g. swap DB without touching UI).

🔥 Past Papers

• 2022 Q7(a), 8 marks — 3-tier architecture
• 2025 Q8(c), 8 marks — same question, repeated verbatim
• → Highest-confidence "will repeat" item on the whole syllabus.

⚠️ MCQ Trap

• "Presentation / logic / data" tiers = architectural design, not implementation.