Re: Link relation types for non-GET links

Hi Klaus,

You can use a standard HAL link and a link relation if you ensure the link
relation is a URL which can be dereferenced to retrieve a machine-readable
description of the methods and messages that are possible for that link.
Just think of it as machine readable link relation documentation.

Cheers,
M

Sent from my mobile
On 6 Aug 2015 13:33, "Klaus Hartke" <hartke@tzi.org> wrote:

> Hi link relation type experts,
>
> I'm using links in my application to discover resources, and link
> relation types to indicate the semantics of a link. Now I'm stumbling
> on links that change the resource state when followed (i.e., links
> that cause requests with methods other than GET).
>
> RFC5988 says that link relation types "can specify the behaviours and
> properties of the target resource (e.g., allowable HTTP methods,
> [...])."
>
> However, none of the registered link relation types seems to do this.
> My question is: Have link relation types for non-GET links simply not
> been registered yet, or should a non-GET link perhaps be a different
> hypermedia control?
>
> For example, let's say I have a collection resource and want to
> provide a way for clients to add new collection items. So I would add
> a POST link that, when followed, creates the new item and updates the
> collection. What should the link relation type be in
> "http://example.org/collection has a ??? resource at
> http://example.org/collection"?
>
>   {
>     "_links": {
>       "terms-of-service": {
>         "href": "http://example.org/tos",
>         "type": "text/html"
>       },
>       "???": {
>         "href": "http://example.org/collection/"
>       }
>     }
>   }
>
>   (using HAL-like syntax [1])
>
> Or should I add the equivalent of an HTML form to my media type, and
> have a "form relation type" (for the lack of a better term) to
> identify the semantics? This would allow me to make statements of the
> form "To {relation type} the {context IRI}, make a {method} request to
> {target IRI}", e.g., "To create-a-new-item-in the
> http://example.org/collection, make a POST request to
> http://example.org/collection".
>
>   {
>     "_links": {
>       "terms-of-service": {
>         "href": "http://example.org/tos",
>         "type": "text/html"
>       },
>     },
>     "_forms": {
>       "create-a-new-item-in": {
>         "href": "http://example.org/collection/",
>         "method": "POST",
>         "accept": "application/x-www-form-urlencoded",
>         "fields": [ "firstName", "lastName", "eMail" ]
>       }
>     }
>   }
>
> Would it make sense to have a registry for common form relation types?
>
> Best regards,
> Klaus
>
> [1] https://tools.ietf.org/html/draft-kelly-json-hal-07
>
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