W3C home > Mailing lists > Public > public-ldp-wg@w3.org > November 2012

Re: Creation of Containers

From: Richard Cyganiak <richard@cyganiak.de>
Date: Thu, 8 Nov 2012 16:30:39 +0000
Cc: "public-ldp-wg@w3.org" <public-ldp-wg@w3.org>, "nathan@webr3.org" <nathan@webr3.org>, Niclas Hoyer <niclas@verbugt.de>
Message-Id: <42825683-B90E-4E92-87C4-64866D1F3B1D@cyganiak.de>
To: "Wilde, Erik" <Erik.Wilde@emc.com>

On 8 Nov 2012, at 03:40, Wilde, Erik wrote:
> On 2012-11-07 16:29 , "Richard Cyganiak" <richard@cyganiak.de> wrote:
>> All very true. A couple of things though.
>> 1. I don't think that media types are the answer here. In the RDF world,
>> we've never used media types to distinguish anything besides the choice
>> of serialization format for the payload, which inevitably is an RDF
>> graph. The media type doesn't need to tell us any more than that -- how
>> to get an RDF graph out of the bytes.
> that's true as long as all you want to do is talk about RDF. if you want
> to build meaningful RDF-based interactions, you need media types, that's
> just how the web works. if you are really patient, reading
> https://gist.github.com/2927644 might be interesting. essentially, we are
> where application/xml was a while ago. if all you want to do is exchange
> XML across the web transparently, application/xml is fine. if, however,
> you want to build web-based interactions, you have to be able to talk
> about the nature of these interactions on the level of the web, and that's
> where media types are required. the fact that we just have application/rdf
> (so to speak) today just means that people still see RDF as a data format,
> not as something for building interactions on the web.

HTML does just fine with a single media type. Why not RDF?

I'll go read the thread you linked, anyway.

>> 2. In the RDF world, the semantics of the message is not communicated in
>> a media type but in the RDF vocabularies used within the graph. RDF terms
>> are globally unique, so this is unambiguous, unlike in say JSON where you
>> need media types to distinguish your format from someone else's.
> are you sure about that one? i think this is what started this thread: the
> inability to distinguish whether a server should interpret something as an
> opaque RDF graph (store this set of triples), or actually do something
> based on the interaction semantics.

That seems to be a non-issue for GET, PUT and DELETE. I can kind of see where you're coming from in the case of POST. But even there, the distinction between “take this set of triples, ignoring their semantics” and “take this set of triples, taking their semantics into account” still doesn't seem to call for a different media type. Again, the semantics is in the vocabularies. The fact that in some situations, one may want to exchange RDF graphs while  ignoring their semantics doesn't change that.

> that is exactly what media types give
> you, and what RDF by definition can not do just by itself, since it is
> only a data format: talking about the interaction semantics of what you
> expect to happen when you exchange certain representations.

But you can define RDF vocabulary that specifies the interaction semantics. Or are you somehow disputing that this is possible?

>> 4. This somewhat parallels the situation in HTML, where the interaction
>> semantics are not in the media type but described in the payload --
>> hyperlinks and forms. Although unlike in HTML, our ³forms² probably only
>> need to cover a few hardcoded kinds of actions -- create a new resource
>> in this container, go to the next page, stuff like that.
> interaction semantics in HTML are in the media type,

Well, fair enough, but my point is that you don't need to introduce new media types each time you build a new service with an HTML front-end, because the interaction semantics in HTML are rich enough and generic enough to work for all sorts of services. The same can work for RDF, with the addition of a few vocabularies.

> what you refer to are
> the "human-oriented semantics" that are represented by anchor text and so
> forth. if interaction semantics weren't part of HTML itself, the web as we
> know it (and particularly any agents that crawl and index) would not exist.

I didn't claim that HTML has no interaction semantics. I claimed that the semantics of RDF representations are in the vocabularies used within the graph, and that it is possible to define vocabularies that specify interaction semantics, and that therefore one doesn't need to introduce new media types in order to enable RESTful interactions on the web. One needs new vocabularies. (Such as the terms that LDP introduces.)


> cheers,
> dret.
Received on Thursday, 8 November 2012 16:31:04 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 16:17:33 UTC