The Activity Streams 2.0 context document is a definition file maintained by the W3C Social Web Community Group (SocialCG). This document describes the process and criteria for approving extensions for inclusion in the main Activity Streams 2.0 context document.
Activity Streams 2.0, as described in [[activitystreams-core]] and [[activitystreams-vocabulary]] is a vocabulary for representing social data. It is used by, among others, the [[activitypub]] API and protocol. It is designed to be extensible, so that new terms can be used by publishers and consumers.
Extensions provide at least the following benefits:
Any publisher can define an extension to Activity Streams 2.0, and use it in published documents. For example, a publisher could define an extension that provides a term for the favorite ice cream flavor of a person.
{
"@context": {
"ic": "https://flavors.example/ns/icecream#",
"favoriteIceCreamFlavor": {
"@id": "ic:favoriteIceCreamFlavor",
"@type": "@id"
},
"Chocolate": "ic:Chocolate",
"Vanilla": "ic:Vanilla",
"Strawberry": "ic:Strawberry",
"Pistachio": "ic:Pistachio"
}
}
This publisher, or any other publisher, can create Activity Streams 2.0 documents that use this extension.
{
"@context": [
"https://www.w3.org/ns/activitystreams",
"https://favorites.example/ns/icecream"
],
"id": "https://example.com/people/evan",
"type": "Person",
"name": "Evan Prodromou",
"favoriteIceCreamFlavor": "Pistachio"
}
If the publisher uses different extensions in the same document with the same term(s), they will need to resolve those naming conflicts by hand.
{
"@context": [
"https://www.w3.org/ns/activitystreams",
"https://favorites.example/ns/icecream",
"https://horse.example/ns/colors"
],
"id": "https://example.com/people/evan",
"type": "Person",
"name": "Evan Prodromou",
"favoriteIceCreamFlavor": "ic:Chocolate",
"horseCoatColor": "horse:Chocolate"
}
Any publisher or consumer can implement this extension, subject to the terms of the creator's license(s), if any.
Referencing many extensions can be a burden for publishers and consumers. Although one or two lines in the @context property of the Activity Streams 2.0 document may not be a problem, ten or twenty could be. In addition, the more extensions that are used, the more likely it is that there will be conflicts between terms.
If an extension becomes very popular, it may be useful to include its terms and namespace in the main Activity Streams 2.0 context document. The W3C Social Web Community Group (SocialCG) is responsible for maintaining the Activity Streams 2.0 context document, and can add terms for popular extensions.
Adding the extension terms to the main context document has several benefits. It lets publishers use the extension without having to include an additional line of context. The extension's terms will be available for all documents that use the Activity Streams 2.0 context, without requiring a namespace prefix. It also provides an opportunity for the SocialCG to resolve conflicts between terms in different extensions.
{
"@context": "https://www.w3.org/ns/activitystreams",
"id": "https://example.com/people/evan",
"type": "Person",
"name": "Evan Prodromou",
"favoriteIceCreamFlavor": "Chocolate"
}
This inclusion does not come without a price. First, the Activity Streams 2.0 context document is that much larger, which has a cost in terms of readability, maintainability, and bandwidth used. In addition, there is work for the SocialCG in updating, documenting, harmonizing, and maintaining the context document.
This Report describes the criteria that the SocialCG will use to decide whether the benefits of simplicity and clarity from adding extension terms to the main context document outweigh the costs of doing so. It is a refinement of the W3C's Adding to W3C RDF Namespaces document to the specific needs of the SocialCG, Activity Streams 2.0, and ActivityPub.
Properly implemented, this process provides a way to make Activity Streams 2.0 a continuously evolving vocabulary, serving new needs for developers and users, while maintaining the stability of the core terms.
These are the steps to including an extension in the Activity Streams 2.0 context document.
To be included in the Activity Streams 2.0, extensions SHOULD meet these requirements.
Extensions to be included MAY meet these criteria:
Reviews may be provided by the submitter, other members of the SocialCG, or by one of the dedicated groups that provide horizontal review of W3C specifications. For instructions, see How to get horizontal review, which also includes instructions for self-reviews.
The W3C policy on namespaces has specific requirements for modifying or removing terms from a namespace document such as a JSON-LD context document. In short, terms defined in a Recommendation may not be modified or removed. This would include all published Activity Streams 2.0 and ActivityPub terms.
The SocialCG MAY remove or modify extension terms, recognizing that this will be disruptive to publishers and consumers who depend on the extension term being in the context document. The SocialCG SHOULD NOT remove extension terms without a strong justification. Serious security issues or legal issues, for example, may justify removal. Modifying or removing an extension term MUST be approved by a resolution of the SocialCG.
The SocialCG MAY mark terms as deprecated. Deprecated terms are still part of the context document, but are documented as deprecated. Deprecating a term MUST be approved by a resolution of the SocialCG.
The section on Extensibility in [[activitystreams-core]] says, in part, "Some popular extensions are included in the Activity Streams 2.0 namespace document [...]". It does not define how extensions are added and which criteria are used to decide whether an extension is popular enough to be included.
The section on Extensions in the Activity Streams 2.0 namespace document says, in part, "The extensions must document their terms in a spec-like way at a persistant [sic] URL. Approval of extensions will be by the Social Web WG until it closes, and after that by the followup Community Group. Process and criteria for extensions approval is being finalised and will be described or linked to here in due course."