Specification

Design Documents

Design documents describe how requirements will be implemented. They bridge requirements → implementation → verification.

What They Are For

• Translate requirements into system structure
• Align developers and engineers before implementation
• Define interfaces, data flows, and responsibilities
• Reduce ambiguity in complex systems
• Provide traceability back to requirements

Typical Structure

1. Overview — purpose, scope, assumptions, constraints
2. Requirements reference — links to relevant requirements (traceability matrix optional)
3. High-level architecture — components, responsibilities, data flow
4. Detailed design — data structures, state machines, algorithms, interface definitions
5. Edge cases and failure handling — recovery strategies, validation rules
6. Non-functional considerations — performance, security, maintainability, scalability
7. Open questions / decisions — design trade-offs, alternatives considered

What a Design Document is NOT

• Not a requirements document
• Not a step-by-step implementation script
• Not code (though diagrams and pseudocode are fine)

See also: Requirements Engineering, Pharma Automation Framework

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Requirements Engineering

Requirements describe what the system must achieve, not how. They sit at different levels of abstraction.

Levels of Requirements

1. Business Requirements

The highest-level intent. Expresses why something is needed. Usually stable over time.

“The system shall reduce manual batch configuration errors.”

2. User / Functional Requirements

Describes system behavior from a user or process point of view. Focuses on what the system does.

“The system shall validate all recipe parameters before execution.”

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