W3C home > Mailing lists > Public > public-hydra@w3.org > January 2015

Re: remove hydra:Resource and hydra:Class (ISSUE-90)

From: Kingsley Idehen <kidehen@openlinksw.com>
Date: Wed, 14 Jan 2015 08:47:29 -0500
Message-ID: <54B67371.4030102@openlinksw.com>
To: public-hydra@w3.org
On 1/14/15 4:18 AM, Tomasz Pluskiewicz wrote:
> January 14 2015 9:43 AM, "Ruben Verborgh"<ruben.verborgh@ugent.be>  wrote:
>>> >>Right, but the goal is not to find out whether they are dereferenceable or
>>> >>not but whether it is worth (from the publishers POV) to follow them.
>> >
>> >That's not how they are defined and used in the Hydra Core Vocabulary.
>> >
>>> >>It's like putting URLs in the content (text) of an HTML document vs. marking
>>> >>them up as links.
>> >
>> >I disagree.
>> >With Linked Data, URLs in RDF are links, cfr. what Kingsley said:
>> >
>>> >>You could write a regex that finds all URLs in text,
>>> >>includes all namespace declaration etc. and follows them. Or you just follow
>>> >>things that have been marked as being hyperlinks and thus intended to be
>>> >>followed.
>> >
> But again, as Kingsley said, it's the predicate that informs the client that a URL could be dereferenced. Even if it's just a hint. Think <link />, <a href="" /> and Link: header. What if the server returns a resource like
> {
>    "@context": {
>      "author": "dcterms:author"
>    },
>    "author": { "@id":"http://example/person/Tom"  }
> }
> There is no indication thathttp://example/person/Tom  is or isn't dereferencable. Does that mean that client should not try? Or assume that it's not dereferencable? The only solid way is to declare the dcterms:author relation as a Link.
>> >Users want to be able to follow any URL.
>> >If a URL is not made “clickable”, it's nearly always omission of the publisher.
>> >Then we default to copy/paste, but still dereference.
>> >
>>>> >>>Indeed, every resource that is_not_  labeled with hydra:Resource,
>>>> >>>but still dereferences, is by definition a hydra:Resource.
>>> >>
>>> >>I can see how you come to that conclusion based on its current definition
>>> >>but that wasn't the intention.
>> >
>> >Yeah. To me, an indication that we really need something else.
> Agreed. And I think that the conclusion is logical indeed in light of open world assumption. The problem is that the semantics of hydra:Resource. You cannot infer that a resource is hydra:Resource by using a reasoner for example. This may sound weird that I bring it up but I think that the word semantics is used is a different meaning than it usually is when talking about the Semantic Web.

Yes! Colloquial use of "Semantics" rarely has anything to to with the 
semantics of a relation (predicate/property/verb). In short, colloquial 
use of "Semantics" is more often than not all about "Syntax" :(

I try to explain these issues as follows:

RDF is a Language. When its pitched as a model confusion creeps in fast!

A Language is a framework for using Signs (for Identification), Syntax 
(arrangement of signs rules/grammar), and Relationship Role Semantics 
(meaning of subject, predicate, object relationship roles) for encoding 
and decoding of information.

Information is Data in some Context.

Knowledge is Data in some Comprehensible (inference and reasoning) context.

Data is basically Observation represented by Entity Relations.

If all of the above is true, then we end up with:

1. Sentence (what an RDF triple represents) being a Datum
2. Paragraph being a Relation (collection/group of sentences that share 
a common predicate [a sentence forming relation] -- Data == Relations
3. So called SPARQL Named Graph -- Document Name [used to group sentence 
collections or paragraphs] or Data Source Name .


-- Predicate Definition
-- Relations
[3] http://www.slideshare.net/kidehen/understanding-29894555 - 
-Understanding Data
[4] http://www.jfsowa.com/pubs/fflogic.htm -- Fads & Fallacies about 
Logic .


Kingsley Idehen	
Founder & CEO
OpenLink Software
Company Web: http://www.openlinksw.com
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Received on Wednesday, 14 January 2015 13:47:54 UTC

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