Data — First Principles

1. The Principles

The schema reflects the domain, not the application. If the data model lies, every query lies.

Duplication is a bug waiting to happen. The same fact lives in one place.

Constraints live where the data lives. Application-layer checks are defense, not enforcement.

Schema changes are reversible, non-destructive, and tested. Production data is sacred.

Indexes exist for known query patterns. Every index earns its write cost.

Same concept, same name, always. Across tables, columns, code, and APIs.

Types match domain meaning. A string is rarely the right type for an email, an ID, or a status.

Data has a creation, a lifetime, and an end. Archival and deletion are first-class.

Relationships are enforced, not assumed. Foreign keys exist. CASCADE is intentional.

Schema choices have cost. Query plans are reviewed. Cardinality is understood.