content negotiation

The mechanism for selecting the appropriate representation when servicing a request, as described in section 12. The representation of entities in any response can be negotiated (including error responses).

内容折衝

要求を service するときに適当な表現を選択する機構。 任意の応答中の実体の表現は折衝することができる (誤り応答を含む)。

Most HTTP responses include an entity which contains information for interpretation by a human user. Naturally, it is desirable to supply the user with the "best available" entity corresponding to the request. Unfortunately for servers and caches, not all users have the same preferences for what is "best," and not all user agents are equally capable of rendering all entity types. For that reason, HTTP has provisions for several mechanisms for "content negotiation" -- the process of selecting the best representation for a given response when there are multiple representations available.

ほとんどの HTTP 応答は、人間利用者が解釈する情報を含んだ実体を含んでいます。 当然、要求に対応する「利用可能な最善」の実体を利用者に供給するのが望ましいといえます。 サーバーやキャッシュには嬉しくないことですが、 何が「最善」であるかに全ての利用者が同じものを好むわけではありませんし。 全ての利用者エージェントが全ての実体型をレンダリングする能力を等しく有しているわけでもありません。 こうした理由から、 HTTP は「内容折衝」という、 当該応答の複数の表現が利用可能なときに最善の表現を選択する処理のための機構を幾つか用意しています。

Note: This is not called "format negotiation" because the alternate representations may be of the same media type, but use different capabilities of that type, be in different languages, etc.

注意 : 代替表現は同じ媒体型で、その型の異なる能力を使っていたり、 異なる言語で書かれていたりのような場合もあるので、「書式折衝」 とは呼びません。

Any response containing an entity-body MAY be subject to negotiation, including error responses. There are two kinds of content negotiation which are possible in HTTP: server-driven and agent-driven negotiation. These two kinds of negotiation are orthogonal and thus may be used separately or in combination. One method of combination, referred to as transparent negotiation, occurs when a cache uses the agent-driven negotiation information provided by the origin server in order to provide server-driven negotiation for subsequent requests.

entity-body を含んだ任意の実体は、 誤り応答も含めて、折衝の対象にして構いません。 HTTP で可能な内容折衝には2種類あります。 この2種類の折衝は直行するものですから、 別々に使っても構いませんし、組合せても構いません。 組合せる方法の一つは、透過折衝と呼ばれるもので、 起源サーバーが以後の要求についてのサーバー駆動折衝を提供するために提供したエージェント駆動折衝情報をキャッシュが使用するときに行われます。

It is possible to serve data in an HTML page mixed with human-readable and machine-readable data, using RDFa for example. However, as the Architecture of the Web [WEBARCH] and DCAT [VOCAB-DCAT] make clear, a resource, such as a dataset, can have many representations. The same data might be available as JSON, XML, RDF, CSV and HTML. These multiple representations can be made available via an API, but should be made available from the same URL using content negotiation to return the appropriate representation (what DCAT calls a distribution).

Servers should support a Turtle representation, and may support other formats. If more than one representation of the Annotation is available, then the server should support content negotiation. Content negotiation for different serializations is performed by including the desired media type in the HTTP Accept header of the request, however clients cannot assume that the server will honor their preferences [rfc7231].

For HEAD and GET requests, if the server supports content negotiation by format or JSON-LD profile, the response must have a Vary header with Accept in the value [rfc7231].

Content negotiation was explained, HTTP 1.2 will support content negotiation.

For practical purposes, it is important that the rel=self URL only offers a single representation.