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# Core terminology

The following terms describe how Neotoma structures, stores, and evolves memory state. Each maps to a concrete layer of the deterministic state pipeline.

If you are new to Neotoma, read the terms in this order: Source -> Observation -> Entity snapshot -> Relationship -> Memory graph. Then review the [data model walkthrough](/data-model) for end-to-end examples.

| Term | Definition |
| --- | --- |
| State layer | Neotoma's role: a deterministic, immutable structured memory substrate that other layers read and write. |
| Entity | Canonical representation of a person, company, or other object with a deterministic ID. |
| Entity snapshot | Current truth for an entity; computed by merging all observations about that entity. |
| Observation | Granular fact extracted from source; reducers merge observations into entity snapshots. |
| Source | Raw data (file, text, URL, or structured JSON) stored with content-addressed deduplication. |
| Provenance | Origin tracking (source, timestamp, user, interpretation) so every value traces back to its source. |
| Memory graph | The graph of source, observations, entities, relationships, and events with typed edges. |
| Reducer | Deterministic function that merges observations into an entity snapshot; same observations always yield the same snapshot. |
| Relationship | Typed connection between two entities (e.g. SETTLES, REFERS\_TO, PART\_OF). |
| Entity type | Classification (e.g. person, company, invoice) that determines the entity schema and resolution rules. |
| Storing | Uploading and processing source into the memory graph (unstructured or structured). |
| Retrieving | Querying entities, entity snapshots, observations, and related data from the memory graph. |

## Where these terms appear

-   [Architecture](/architecture) · deterministic state pipeline and guarantees
-   [MCP reference](/mcp) · actions that operate on entities, observations, and relationships
-   [CLI reference](/cli) · command-level access to snapshots, observations, and graph operations