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In the high-stakes world of software engineering, a beautifully crafted design means nothing if it crumbles under the weight of real-world requirements. Every experienced engineer has witnessed the painful reality: designs that looked elegant on the whiteboard but failed spectacularly in implementation. The difference between success and failure often lies not in the creativity of the design, but in the rigor of its validation.
Design validation is not a checkpoint you pass through once—it's a continuous discipline that separates professional engineering from amateur experimentation. This page presents a systematic, battle-tested approach to design review that will transform how you evaluate your own work and the work of others.
By the end of this page, you will possess a comprehensive design review checklist that addresses requirements coverage, structural integrity, behavioral correctness, operational readiness, and maintainability. You'll understand not just what to check, but why each checkpoint matters and how to evaluate it effectively.
Before diving into the mechanics of design review, we must understand why this discipline is non-negotiable for professional software development.
The Cost Amplification Effect:
Defects found during design review cost approximately 10-100x less to fix than the same defects discovered during testing, and 100-1000x less than those found in production. This isn't hyperbole—it's empirically validated across thousands of projects. A flawed class hierarchy that takes 30 minutes to reconsider during design can require weeks of painful refactoring once code is written, tests are in place, and dependencies have formed.
The Knowledge Crystallization Problem:
While you're actively designing, you hold the entire context in your mind: the requirements, the constraints, the alternatives you considered and rejected, the subtle reasoning behind each decision. This knowledge evaporates rapidly. A design you created last week is already harder to understand than one you finished yesterday. Systematic review captures and validates this knowledge before it fades.
| Discovery Phase | Relative Cost | Impact | Recovery Difficulty |
|---|---|---|---|
| Design Review | 1x (baseline) | Easily corrected on paper | Trivial—redraw diagram |
| Implementation | 10-25x | Code rewrite required | Moderate—localized changes |
| Unit Testing | 25-50x | Cascading test failures | Significant—multiple components |
| Integration Testing | 50-100x | Cross-component breakage | High—coordination required |
| Production | 100-1000x | Customer impact, reputation | Extreme—emergency response |
Teams that skip design review to 'move faster' invariably end up slower. The time 'saved' by rushing through design is repaid with compound interest during debugging, refactoring, and production firefighting. Design review is not overhead—it's an investment that pays dividends throughout the project lifecycle.
Effective design review requires a structured framework that ensures comprehensive coverage while remaining practical to apply. The following framework organizes review activities into five interconnected dimensions, each addressing a critical aspect of design quality.
The Five Dimensions of Design Validation:
Each dimension contains specific checkpoints that together form a complete validation regime. Unlike ad-hoc review, this structured approach ensures that critical aspects are never overlooked, regardless of time pressure or reviewer fatigue.
The Checkpoint Mindset:
Each checkpoint in our framework is formulated as a concrete, answerable question. Vague checkpoints like 'Is the design good?' are useless—they invite subjective hand-waving and miss specific issues. Instead, we ask precise questions: 'Does every class have a single, well-defined responsibility?' This precision enables objective evaluation and constructive discussion.
The most fundamental design failure is building the wrong thing. Requirements alignment ensures that before evaluating how well something is designed, we confirm that it addresses the actual problem.
Functional Requirements Coverage:
Non-Functional Requirements Coverage:
Non-functional requirements (NFRs) are frequently neglected during design, then discovered as crises during load testing or production deployment. Proactive validation prevents these surprises:
If your design satisfies all stated requirements but feels incomplete, trust that instinct. Ask: 'What will users expect that wasn't explicitly written?' Requirements documents capture the obvious cases—experienced designers anticipate the implicit expectations and error conditions.
Structural integrity addresses the internal coherence of the design—whether classes and components are well-formed, properly organized, and correctly related to each other.
Class Design Quality:
Relationship Validation:
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// BEFORE: Poor Structural Integrityclass OrderProcessor { private database: DatabaseConnection; private emailService: EmailService; private paymentGateway: PaymentGateway; private inventorySystem: InventorySystem; private reportGenerator: ReportGenerator; // This class does too many things - violates Single Responsibility processOrder(order: Order): void { // Validates order // Processes payment // Updates inventory // Sends confirmation email // Generates sales report // All in one massive method }} // AFTER: Proper Structural Integrityclass OrderProcessor { constructor( private orderValidator: OrderValidator, private paymentProcessor: PaymentProcessor, private orderFulfillment: OrderFulfillment ) {} // Single, clear responsibility: orchestrating order processing async processOrder(order: Order): Promise<OrderResult> { const validationResult = await this.orderValidator.validate(order); if (!validationResult.isValid) { return OrderResult.validationFailed(validationResult.errors); } const paymentResult = await this.paymentProcessor.process(order); if (!paymentResult.isSuccessful) { return OrderResult.paymentFailed(paymentResult.error); } await this.orderFulfillment.fulfill(order, paymentResult.transactionId); return OrderResult.success(order.id); }} // Each class now has a single, focused responsibilityclass OrderValidator { validate(order: Order): Promise<ValidationResult> { /* ... */ }} class PaymentProcessor { constructor(private paymentGateway: PaymentGateway) {} process(order: Order): Promise<PaymentResult> { /* ... */ }} class OrderFulfillment { constructor( private inventoryService: InventoryService, private notificationService: NotificationService ) {} fulfill(order: Order, transactionId: string): Promise<void> { /* ... */ }}When reviewing structural integrity, apply the 'smell test': Does this structure feel right? Would you be comfortable explaining this design to a senior colleague? If you find yourself making excuses or qualifications, the structure likely needs improvement.
A structurally sound design can still produce incorrect behavior. Behavioral correctness validates that the design will do the right thing in all scenarios, including edge cases and error conditions.
State Machine Validation:
Edge Case Analysis:
| Edge Case Category | Examples | Design Questions |
|---|---|---|
| Empty/Zero | Empty collections, zero quantities, null values | Does the design handle absence gracefully? |
| Boundary Values | Minimum values, maximum values, exactly at limits | Are boundary conditions explicitly tested in logic? |
| Concurrency | Simultaneous operations, race conditions | Are shared resources protected? Is ordering guaranteed where needed? |
| Failure/Timeout | Network failures, timeouts, resource exhaustion | Are failure paths designed? Do partial failures leave consistent state? |
| Security Edge Cases | Invalid inputs, injection attempts, authorization bypass | Is all input validated? Are security boundaries explicitly enforced? |
Designs that work perfectly in development can fail dramatically in production if operational concerns are neglected. Operational readiness ensures that the design can be deployed, monitored, and maintained by operations teams.
Deployment Readiness:
Observability Design:
Imagine being called at 3 AM because this component is failing. Can you diagnose the problem from logs and metrics without access to code? If not, the operational design is incomplete. Every production system should be debuggable by an on-call engineer with only external observations.
Software that cannot evolve is software that will be replaced. Evolution capability ensures that the design can accommodate anticipated changes without requiring fundamental restructuring.
Anticipated Change Analysis:
Interface Stability:
If you cannot envision how this design would accommodate change requests two years from now, it probably lacks sufficient flexibility. While we cannot predict specific changes, well-designed systems have the vocabulary and structure to discuss and implement future requirements.
Having a checklist is necessary but not sufficient—you also need an effective process for applying it. The following process has been refined through thousands of design reviews across many organizations:
Phase 1: Self-Review (30-60 minutes)
Before involving others, conduct a systematic self-review using the checklist. This catches obvious issues and forces you to articulate your reasoning. Walk through each dimension methodically, documenting answers to each checkpoint. This preparation ensures external reviewers spend time on genuine design challenges, not obvious oversights.
Phase 2: Peer Review (45-90 minutes)
Present the design to one or more peers with relevant domain or technical expertise. The goal is not approval—it's improvement. Effective peer reviews follow these principles:
Phase 3: Resolution and Documentation
After review, update the design to address blocking issues and document decisions about deferred issues. Create a design decision record (DDR) that captures:
This documentation is invaluable when future developers ask 'Why was it done this way?' The answer is preserved, not lost with the original designer.
You now possess a comprehensive framework for design review, encompassing requirements alignment, structural integrity, behavioral correctness, operational readiness, and evolution capability. The next page focuses specifically on SOLID principle compliance—a critical subset of structural integrity that deserves deep examination.