ActivityStreams 2.0 Overview

ActivityStreams 2.0 is the vocabulary that ActivityPub uses to represent social data. It defines the format for activities, actors, objects, and collections using JSON-LD.

Specification

• Status: W3C Recommendation (May 2017)
• Core: https://www.w3.org/TR/activitystreams-core/
• Vocabulary: https://www.w3.org/TR/activitystreams-vocabulary/

The JSON-LD Context

Every ActivityStreams document includes a context:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Note",
  "content": "Hello, world!"
}

The context maps short property names to full URIs:

• type → https://www.w3.org/ns/activitystreams#type
• content → https://www.w3.org/ns/activitystreams#content

Core Types

Object

The base type for all things:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Object",
  "id": "https://example.com/objects/1",
  "name": "A simple object"
}

Activity

An action performed by an actor:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Create",
  "actor": "https://example.com/users/alice",
  "object": {
    "type": "Note",
    "content": "Hello!"
  }
}

Actor

An entity that can perform activities:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Person",
  "id": "https://example.com/users/alice",
  "name": "Alice"
}

Collection

A group of items:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Collection",
  "totalItems": 2,
  "items": [
    { "type": "Note", "content": "First" },
    { "type": "Note", "content": "Second" }
  ]
}

Type Hierarchy

Object
├── Activity
│   ├── Create
│   ├── Delete
│   ├── Update
│   ├── Follow
│   ├── Accept
│   ├── Reject
│   ├── Like
│   ├── Announce
│   └── ... (more)
├── Actor
│   ├── Person
│   ├── Organization
│   ├── Application
│   ├── Service
│   └── Group
├── Object Types
│   ├── Note
│   ├── Article
│   ├── Image
│   ├── Video
│   ├── Audio
│   └── ... (more)
├── Collection
│   └── OrderedCollection
└── Link

Common Properties

Identity

Property	Type	Description
id	URL	Unique identifier
type	String	Object type
name	String	Display name
summary	String	Short description

Authorship

Property	Type	Description
attributedTo	Actor	Creator
actor	Actor	Activity performer

Content

Property	Type	Description
content	String	Main content (HTML)
contentMap	Object	Localized content
mediaType	String	MIME type

Timestamps

Property	Type	Description
published	DateTime	Creation time
updated	DateTime	Last modified
startTime	DateTime	Event start
endTime	DateTime	Event end

Addressing

Property	Type	Description
to	Array	Primary recipients
cc	Array	Secondary recipients
bto	Array	Private primary
bcc	Array	Private secondary

Extending ActivityStreams

Custom Properties

Add properties via the context:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    {
      "sensitive": "as:sensitive",
      "toot": "http://joinmastodon.org/ns#",
      "blurhash": "toot:blurhash"
    }
  ],
  "type": "Note",
  "content": "Hidden content",
  "sensitive": true
}

Custom Types

Define new types:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    {
      "Emoji": "toot:Emoji"
    }
  ],
  "type": "Emoji",
  "name": ":awesome:",
  "icon": {
    "type": "Image",
    "url": "https://example.com/emoji/awesome.png"
  }
}

Processing ActivityStreams

Parsing

function parseActivityStreams(json) {
  // Normalize to array context
  let context = json['@context'];
  if (!Array.isArray(context)) {
    context = [context];
  }

  // Get type
  const type = json.type;

  // Handle multiple types
  const types = Array.isArray(type) ? type : [type];

  return {
    context,
    types,
    data: json
  };
}

Type Checking

function isActivity(obj) {
  const activityTypes = [
    'Create', 'Update', 'Delete', 'Follow',
    'Accept', 'Reject', 'Like', 'Announce', 'Undo'
  ];
  return activityTypes.includes(obj.type);
}

function isActor(obj) {
  const actorTypes = [
    'Person', 'Organization', 'Application', 'Service', 'Group'
  ];
  return actorTypes.includes(obj.type);
}

See Also

• Core Types - Base types
• Activity Types - All activities
• Object Types - Content types
• Properties - All properties