> ## Documentation Index > Fetch the complete documentation index at: https://docs.getcanonic.app/llms.txt > Use this file to discover all available pages before exploring further. # The three layers > Semantics, knowledge, and contracts, and the split rule for where new context belongs. canonic's context lives in three committed surfaces: plain files in your git repo, reviewed like code. Each answers a different question. | Layer | File | Answers | Owned by | | ------------- | --------------------- | ---------------------------------------------------------------------- | --------------- | | **Semantics** | `semantics/**/*.yaml` | "How do I query this safely?": tables, types, grains, joins, measures | auto-maintained | | **Knowledge** | `knowledge/**/*.md` | "What does this mean to the business?": definitions, caveats, policies | auto-maintained | | **Contracts** | `contracts/**/*.yaml` | "Which definition is canonical, and what must the answer obey?" | human-owned | ## The split rule * Changes how the SQL *runs* → [**semantics**](/concepts/semantics). * A human needs it to *trust* the answer → [**knowledge**](/concepts/knowledge-layer). * Governs *which* definition is authoritative or *what an answer must satisfy* → [**contracts**](/concepts/contracts-and-guardrails). The key idea: a knowledge page *explains* why "amount includes refunds unless filtered." A contract *makes the SQL obey* it. Documented caveats become enforced guardrails, so the warning can't be silently ignored. ## Why three surfaces, not one Each layer has a different owner and a different update cadence: * **Semantics** is machine-derived from your live schema (tables, columns, grains, joins) and safe to auto-refresh on every [`canonic ingest`](/cli-reference/ingest): it describes physical reality, so it should track physical reality. * **Knowledge** carries business prose that's also auto-drafted from evidence (dbt descriptions, Notion pages, BI usage), but is meant to be refined by a human over time: it's read-heavy context, not enforcement. * **Contracts** decide what's *authoritative* and *mandatory*. This is deliberately human-owned: which of two conflicting "revenue" definitions wins, and which guardrails are non-negotiable, are governance decisions canonic surfaces but never makes for you. This is also why ingestion is [propose-only](/concepts/ingestion-and-reconciliation): a `human_curated` or `board_approved` fact in any layer is never silently overwritten by new evidence; at most, a conflict is flagged for review. Tables, grains, joins, and measures: what the compiler queries against. Business meaning, caveats, and policies: searchable and graph-linked. Canonical bindings and guardrails: what the compiler must obey.