How should a default country be modeled for address validation?

How should a default country be modeled for address validation?

• A. Use language
• B. Use IP geolocation
• C. Use country_code to drive format and validation rules
• D. Use a fixed global format

Answer: (C)

The main idea is that address validation must be country-specific, and the way you determine which rules to apply should come from the country itself. Using the country_code to drive format and validation rules lets you load the exact address schema for that country: which fields are required, the order of those fields, the permitted characters, and the correct postal code pattern. This approach ensures the system validates and formats addresses in a way that matches real-world postal standards—for example, US addresses use ZIP+4 and include state, while the UK uses a different alphanumeric postcode system and regional divisions, and Japan relies on prefectures and a distinct postal format. Language alone doesn’t reliably indicate the country or its address structure, and IP geolocation can be inaccurate or misleading, especially for travelers or users behind VPNs. A fixed global format ignores the vast differences in address conventions, leading to incorrect validation and poor user experience. By tying the default or current validation rules to the country_code, you apply the correct, localized rules consistently and can fall back to a sensible default only when the country is known, keeping the validation precise and flexible.