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RE: hydra:returns for operations returning collections of class instances

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Wed, 18 Jun 2014 14:21:40 +0200
To: <public-hydra@w3.org>
Message-ID: <001701cf8aef$dc831a30$95894e90$@gmx.net>
On 17 Jun 2014 at 10:29, Jindřich Mynarz wrote:
> if a hydra:Operation returns a hydra:Collection of instances of class
> :Class, should the hydra:returns of the operation be set to
> hydra:Collection or :Class?

That's a good question. The "main entity" that is returned is a collection but the thing the client is probably interested in are the instances of :Class. I'd say the best thing would be to be more explicit, i.e., expressing that it returns a Collection of :Class instances. This would be quite trivial to describe with OWL (property restriction on member).

> For example, the Issue tracker demo
> (http://www.markus-lanthaler.com/hydra/api-demo/vocab#) describes an
> operation _:user_raised_issues_retrieve, which returns
> hydra:Collection instead of vocab:Issue. Similarly, the
> vocab:User/raisedIssues property, which supports this operation, is
> defined with the rdfs:range set to hydra:Collection.

The range has to be set to Collection as otherwise the collection is inferred to be of type Issue, which it isn't.

> Is this a counter-measure for the issue of hydra:Collections
> "breaking" relationships (ISSUE #41)?

It is an option yeah. It just describes what happens. hydra:returns, however, returns to little information to be useful in this case.

Markus Lanthaler
Received on Wednesday, 18 June 2014 12:22:09 UTC

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