W3C home > Mailing lists > Public > public-ldp@w3.org > March 2013

Re: Section 4: LDPR/non-LDPR formal definitions

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sat, 23 Mar 2013 13:27:59 +0000
Cc: Richard Cyganiak <richard@cyganiak.de>, Henry Story <henry.story@bblfish.net>, Martynas Jusevičius <martynas@graphity.org>, public-ldp@w3.org
Message-Id: <7C4EC9A2-FB40-472D-BF5B-1F610322E037@cyganiak.de>
To: Erik Wilde <dret@berkeley.edu>
On 23 Mar 2013, at 01:20, Erik Wilde <dret@berkeley.edu> wrote:
> pretty much any media type i know has assumptions around where a link takes you. it may take you to a resource that supports the same media type, or not. while technically speaking, no media type should make assumptions about that, many applications will. when you follow an HTML img/@src link, you expect an image/* response, or you don't really know what to do. same for a/@href, you expect an HTML page, or you don't really know what to do.

In the context of RDF, I would expect applications to be guided by the property (a.k.a. link type) of the triple. If I see a foaf:homepage triple, I'd expect an HTML response. For foaf:depiction, an image response. For foaf:knows, an RDF response (perhaps after the usual follow-your-nose hash-stripping and 303-redirecting dance).

> so what a media type might want to say is when links are "within" the media type (linkage between various resources exposed through that media type), and when they (potentially) "leave" the media type. this is helpful for clients to know, even though strictly speaking it would be best to never make any assumptions about this.

We've had this discussion before. In the context of RDF, the media type (say, text/turtle) essentially delegates this question to vocabularies. If a client knows a particular vocabulary (say, FOAF), then all is good; it knows what to expect for any given property. If the client doesn't know the vocabulary, then at least it knows that here's some sort of relationship to some sort of web resource, but it won't know what to expect at the other end.

So the story for RDF is a bit more complex than for other media types. RDF itself has no semantics whatsoever; it just provides a bag of triples. All the semantics in an RDF representation come from the vocabularies used in the representation. To paint the full picture of RESTful interactions with RDF, it's not sufficient to talk about media types; one also needs to talk about the vocabularies that a particular client understands. (But vocabularies can be seen as an extension mechanism provided by the media type, I suppose.)

Richard



> i do agree that it is not necessary to define "non-LDP" resources. what you find and what it means to you is determined by the link you follow, and the media type you get when you follow it. that's all clients need to know.
> 
> cheers,
> 
> dret.
> 
Received on Saturday, 23 March 2013 13:28:19 UTC

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