# Digital Objects (/build/concepts/digital-objects)



Every entity in headless.ly is a **Digital Object** — a typed, versioned, event-sourced entity with an immutable history, relationships to other objects, and actions you can perform on it.

Defining a Noun [#defining-a-noun]

Entities are defined using the `Noun()` function from `digital-objects`. Zero dependencies. Zero codegen. Full TypeScript inference.

```typescript
import { Noun } from 'digital-objects'

export const Contact = Noun('Contact', {
  name: 'string!',
  email: 'string?#',
  phone: 'string?',
  title: 'string?',
  stage: 'Lead | Qualified | Customer | Churned | Partner',
  source: 'string?',
  organization: '-> Organization.contacts',
  deals: '<- Deal.contact[]',
  messages: '<- Message.contact[]',

  qualify:  'Qualified',
  capture:  'Captured',
  assign:   'Assigned',
  merge:    'Merged',
  enrich:   'Enriched',
})
```

Property Value Patterns [#property-value-patterns]

Every property value tells the parser what it is:

| Pattern                   | Meaning                   | Example                                             |
| ------------------------- | ------------------------- | --------------------------------------------------- |
| Type string               | Data property             | `'string!'`, `'number?'`, `'datetime!'`             |
| Arrow syntax              | Relationship              | `'-> Organization.contacts'`, `'<- Deal.contact[]'` |
| Pipe-separated PascalCase | Enum                      | `'Lead \| Qualified \| Customer'`                   |
| Single PascalCase word    | Verb declaration          | `'Qualified'`, `'Captured'`                         |
| `null`                    | Opt out of inherited verb | `update: null`                                      |

Type Modifiers [#type-modifiers]

| Modifier | Meaning  |
| -------- | -------- |
| `!`      | Required |
| `?`      | Optional |
| `#`      | Indexed  |

Relationships [#relationships]

```typescript
organization: '-> Organization.contacts'     // belongs to Organization
deals: '<- Deal.contact[]'         // has many Deals
```

`->` is a forward reference (many-to-one). `<-` is a reverse reference (one-to-many). `[]` indicates a collection.

Immutability [#immutability]

Opt out of CRUD verbs with `null`:

```typescript
export const Event = Noun('Event', {
  name: 'string!',
  timestamp: 'datetime!',
  update: null,
  delete: null,
})
```

`Event.update()` is a TypeScript error — the Noun definition above removes it.