# Entities

Find the owner and reference for every Communication table.

The base has 13 tables and 215 fields. Four native tables hold channels, bindings, rules and deliveries; nine mirrors bring shared identities, catalogs and tools from Core and Tooling and Access.

| Table | Documentation | Ownership | Fields |
| --- | --- | --- | --- |
| Channel | [Open reference](/systems/communication/entity-channel) | Communication | 13 |
| Channel Binding | [Open reference](/systems/communication/entity-channel-binding) | Communication | 13 |
| Notification Rule | [Open reference](/systems/communication/entity-notification-rule) | Communication | 15 |
| Message | [Open reference](/systems/communication/entity-message) | Communication | 23 |
| Organization (mirror) | [Open reference](/systems/communication/entity-organization) | Core | 28 |
| Person (mirror) | [Open reference](/systems/communication/entity-person) | Core | 19 |
| Membership (mirror) | [Open reference](/systems/communication/entity-membership) | Core | 22 |
| Department (mirror) | [Open reference](/systems/communication/entity-department) | Core | 11 |
| Team (mirror) | [Open reference](/systems/communication/entity-team) | Core | 11 |
| Tool (mirror) | [Open reference](/systems/communication/entity-tool) | Tooling and Access | 13 |
| Tool Workspace (mirror) | [Open reference](/systems/communication/entity-tool-workspace) | Tooling and Access | 15 |
| Classification Term (mirror) | [Open reference](/systems/communication/entity-classification-term) | Core | 15 |
| Tags (mirror) | [Open reference](/systems/communication/entity-tags) | Core | 17 |

## Cardinality and identifiers

Every link in this base is a multiple-record link, including those whose description says "link exactly one" (Channel Binding → Channel, Notification Rule → Channel, Message → Channel). The single-link rule is guidance, not a database constraint. One Channel can have many Bindings, Rules and Messages. One Rule can produce many Messages. A Message can reply to one earlier Message through In Reply To.

External Message Id is the tool's own message key (for Slack, the message timestamp). Membership # joins a recipient across bases; Airtable record IDs are local to each base and never cross. Thread Id groups e-mail messages of one conversation; Context Base and Context Key point at a record in another base as text, because Airtable cannot link across bases.