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Squaring the HTTP-range-14 circle [was Re: Schema.org in RDF ...]

From: Danny Ayers <danny.ayers@gmail.com>
Date: Sun, 12 Jun 2011 14:40:18 +0200
Message-ID: <BANLkTimB9Qw51jXBPmpG-TV+TSOzkvXeRA@mail.gmail.com>
To: Pat Hayes <phayes@ihmc.us>
Cc: Richard Cyganiak <richard@cyganiak.de>, Alan Ruttenberg <alanruttenberg@gmail.com>, Linked Data community <public-lod@w3.org>, Michael Hausenblas <michael.hausenblas@deri.org>
On 12 June 2011 01:51, Pat Hayes <phayes@ihmc.us> wrote:
>
> On Jun 11, 2011, at 12:20 PM, Richard Cyganiak wrote:
>
>> ...
>>>> It's just that the schema.org designers don't seem to care much about the distinction between information resources and angels and pinheads. This is the prevalent attitude outside of this mailing list and we should come to terms with this.
>>>
>>> I think we should foster a greater level of respect for representation
>>> choices here. Your dismissal of the distinction between information
>>> resources and what they are about insults the efforts of many
>>> researchers and practitioners and their efforts in domains where such
>>> a distinction in quite important. Let's try not to alienate part of
>>> this community in order to interoperate with another.
>>
>> Look, Alan. I've wasted eight years arguing about that shit and defending httpRange-14, and I'm sick and tired of it. Google, Yahoo, Bing, Facebook, Freebase and the New York Times are violating httpRange-14. I consider that battle lost. I recanted. I've come to embrace agnosticism and I am not planning to waste any more time discussing these issues.
>
>
> Well, I am sympathetic to not defending HTTP-range-14 and nobody ever, ever again even mentioning "information resource", but I don't think we can just make this go away by ignoring it. What do we say when a URI is used both to retrieve, um sorry, identify, a Web page but is also used to refer to something which is quite definitely not a web page? What do we say when the range of a property is supposed to be, say, people, but its considered OK to insert a string to stand in place of the person? In the first case we can just say that identifying and reference are distinct, and that one expects the web page to provide information about the referent, which is a nice comfortable doctrine but has some holes in it. (Chiefly, how then do we actually refer to a web page?) But the second is more serious, seems to me, as it violates the basic semantic model underlying all of RDF through OWL and beyond. Maybe we need to re-think this model, but if so then we really ought to be doing that re-thinking in the RDF WG right now, surely? Just declaring an impatient agnosticism and refusing to discuss these issues does not get things actually fixed here.

For pragmatic reasons I'm inclined towards Richard's pov, but it would
be nice for the model to make sense.

Pat, how does this sound:

>From HTTP we get the notions of resources and representations. The
resource is the conceptual entity, the representations are concrete
expressions of the resource. So take a photo of my dog -

<http://example.org/sasha-photo> foaf:depicts <http://example.org/Sasha> .

If we deref http://example.org/sasha-photo then we would expect to get
a bunch of bits that can be displayed as an image.

But that bunch of bits may be returned with HTTP header -

Content-Type: image/jpeg

or

Content-Type: image/gif

Which, for convenience, lets say correspond to files on the server
called sasha-photo.jpg and sasha-photo.gif

Aside from containing a different bunch of bits because of the
encoding, sasha-photo.jpg could be a lossy-compressed version of
sasha-photo.gif, containing less pixel information yet sharing many
characteristics.

All ok so far..?

If so, from this we can determine that a representation of a resource
need not be "complete" in terms of the information it contains to
fulfill the RDF statement and the HTTP contract.

Now turning to http://example.org/Sasha, what happens if we deref that?

Sasha isn't an information resource, so following HTTP-range-14 we
would expect a redirect to (say) a text/html description of Sasha.

But what if we just got a 200 OK and some bits Content-Type: text/html ?

We are told by this that we have a representation of my dog, but from
the above, is there any reason to assume it's a complete
representation?

The information would presumably be a description, but is it such a
leap to say that because this shares many characteristics with my dog
(there will be some isomorphism between a thing and a description of a
thing, right?) that this is a legitimate, however partial,
representation?

In other words, what we are seeing of my dog with -

Content-Type: text/html.

is just a very lossy version of her representation as -

Content-Type: physical-matter/dog

Does that make (enough) sense?

Cheers,
Danny.




-- 
http://danny.ayers.name
Received on Sunday, 12 June 2011 12:40:46 UTC

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