---
title: Overview
description: Shape the data your app adds to a workspace — objects, fields, and relations.
icon: "database"
---

A Twenty app's **data layer** is the data your app *adds* to a workspace — the new record types it declares, the columns it adds to existing objects, and how those records connect to each other.

```text
┌──────────────────────────────────────────────────┐
│ Object — a record type, e.g. PostCard            │
│    ├─ Field     (name, type, label)              │
│    ├─ Field                                      │
│    └─ Relation  (link to another object)         │
└──────────────────────────────────────────────────┘
            │
            ├── lives in your app, OR
            │
            ▼
┌──────────────────────────────────────────────────┐
│ Standard / other apps' objects                   │
│    └─ Field added by your app via defineField    │
└──────────────────────────────────────────────────┘
```

## In this section

<CardGroup cols={2}>
  <Card title="Objects" icon="table" href="/developers/extend/apps/data/objects">
    `defineObject` — declare new record types with their own fields.
  </Card>
  <Card title="Extending Objects" icon="wand-magic-sparkles" href="/developers/extend/apps/data/extending-objects">
    `defineField` — add fields to standard or other apps' objects.
  </Card>
  <Card title="Relations" icon="diagram-project" href="/developers/extend/apps/data/relations">
    Bidirectional `MANY_TO_ONE` / `ONE_TO_MANY` connections between objects.
  </Card>
</CardGroup>

## Entities at a glance

| Entity | Purpose | Defined with |
|--------|---------|--------------|
| **Object** | A new custom record type (e.g. PostCard, Invoice) with its own fields | `defineObject()` |
| **Field** | A column on an object. Standalone fields can extend objects you didn't create (e.g. add `loyaltyTier` to Company) | `defineField()` |
| **Relation** | A bidirectional link between two objects — both sides declared as fields | `defineField()` with `FieldType.RELATION` |

The SDK detects these via AST analysis at build time, so file organization is up to you — the convention is `src/objects/` and `src/fields/`. Stable `universalIdentifier` UUIDs tie everything together across deploys.

<Note>
Looking for **Application Config** or **Roles & Permissions**? Those describe the app itself rather than the data it adds — they live under [Config](/developers/extend/apps/config/overview). Looking for **Connections** (Linear, GitHub, Slack OAuth)? Those exist to be called *from* logic functions and live under [Logic](/developers/extend/apps/logic/connections).
</Note>