Definition
Single Source of Truth
A single source of truth is a design principle where every piece of data has exactly one authoritative, canonical home, and all other views derive from it. Instead of the same fact living in several places that can drift apart, one record is definitive. It eliminates contradictory copies, so there is never ambiguity about which value is correct.
Key takeaways
- A single source of truth gives every fact exactly one authoritative home, with all other views derived from it.
- It eliminates contradictory duplicate copies that inevitably drift apart, so the correct value is never ambiguous.
- Derived data — caches, indexes, dashboards, replicas — is fine, but must be clearly downstream and reconcilable to the source.
- The benefit is consistency and trust; the cost is the discipline to avoid convenient second copies and to keep derived views in sync.
When the same information is duplicated across systems — a customer's status in the CRM, the billing system, and a spreadsheet — those copies inevitably diverge, and you're left guessing which one is right. A single source of truth (SSOT) resolves this by designating one authoritative store for each fact. Everything else references or is derived from it, so there is exactly one place to read and exactly one place to update.
The principle applies at every layer. In a database it means normalizing data so a fact isn't redundantly stored; in an architecture it means one service owns each domain; in a team it means one document or system is canonical and the rest are mirrors. Derived data — caches, search indexes, dashboards, replicas — is allowed, but it must be clearly downstream and reconcilable back to the source.
The benefit is consistency and trust: decisions and automations built on the data don't have to reconcile conflicting copies. The cost is discipline — you must resist the convenience of stashing a quick second copy, and you must build the pipelines that keep derived views in sync.
In Planoda, the database schema is the single source of truth from which API contracts and validation are generated, so the shape of the data is defined in exactly one place.
Related terms
- Infrastructure as Code (IaC)Infrastructure as code is the practice of defining and provisioning servers, networks, databases, and other infrastructure through machine-readable configuration files rather than manual setup. Because the definition lives in version control, environments become reproducible, reviewable, and auditable — you can recreate or change infrastructure by editing code rather than clicking through a console.
- Transactional OutboxThe transactional outbox is a reliability pattern that guarantees a side effect — a webhook, an event, a notification — fires exactly when its database change commits, and never otherwise. The action is written to an outbox table inside the same transaction as the data change, then a separate process delivers it, eliminating the lost or phantom events that plague naive 'save then send' code.
- Eventual ConsistencyEventual consistency is a guarantee in distributed systems that, if no new updates are made, all replicas of the data will converge to the same value — eventually. It accepts that reads may briefly see stale data in exchange for higher availability and lower latency, trading the strict immediacy of strong consistency for resilience and scale.
- Audit TrailAn audit trail is an append-only, time-ordered record of who did what, when, and to which object across a system. Every create, edit, delete, and approval is logged immutably, so any state can be traced back to the actions that produced it. Audit trails underpin accountability, debugging, compliance, and — increasingly — oversight of what AI agents do.
- Row-Level Security (RLS)Row-level security (RLS) is a database feature that restricts which rows a query can read or modify based on the current user or context. Instead of relying solely on application code to filter data, the database itself enforces access policies on every query — a strong defense for multi-tenant systems where one workspace's data must never leak to another.