System Design Basics
Chapter 1: Understanding the fundamentals of application planning
What Makes a Great Specification?
A great specification document is the bridge between your business vision and technical implementation. It translates what you want into what developers can build, eliminating ambiguity and reducing costly revisions.
The Five Core Principles
1. Start with the Why
Before describing features, explain the business problem you're solving. Context helps developers make better decisions when facing implementation choices.
2. Define Clear Boundaries
Explicitly state what's included AND what's not included. This prevents scope creep and ensures everyone has the same expectations.
3. Use Concrete Examples
Abstract descriptions lead to misunderstandings. Provide specific scenarios, sample data, and real-world use cases.
4. Prioritize Requirements
Mark features as "Must Have", "Should Have", or "Nice to Have". This helps developers focus on critical functionality first.
5. Define Success Metrics
How will you know the application meets your needs? Include measurable criteria for performance, usability, and business outcomes.
Pro Tip
Think of your specification as a contract. If it's not written down, it's not guaranteed to be built. Be explicit about every important detail.
Common Pitfalls to Avoid
Pitfall 1: Technical Solutioning
Don't tell developers HOW to build it (unless critical). Focus on WHAT you need and WHY. Let experts choose the best implementation.
Pitfall 2: Assuming Context
Developers aren't mind readers. Don't assume they understand your industry jargon, business processes, or implicit requirements.
Pitfall 3: Kitchen Sink Syndrome
Listing every possible feature without prioritization leads to bloated, expensive applications. Focus on core functionality first.
The Requirements Hierarchy
- Business Objectives: What business goals will this achieve?
- User Stories: Who will use it and what will they accomplish?
- Functional Requirements: What specific features are needed?
- Non-Functional Requirements: Performance, security, usability standards
- Constraints: Technical, budget, or timeline limitations
- Acceptance Criteria: How to verify each requirement is met