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Re: What should we call RDF's ability to allow multiple models to peacefully coexist, interconnected?

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 8 Mar 2014 11:25:18 -0600
Cc: David Booth <david@dbooth.org>, "Timothy W. Cook" <tim@mlhim.org>, semantic-web <semantic-web@w3.org>
Message-Id: <5BA27EE1-8394-46AC-AD25-E1DC863171AC@ihmc.us>
To: Graham Klyne <GK@ninebynine.org>

On Mar 8, 2014, at 8:36 AM, Graham Klyne <GK@ninebynine.org> wrote:

> On 07/03/2014 20:09, David Booth wrote:
>> On 03/07/2014 02:33 PM, Timothy W. Cook wrote:
>>> [ . . . ]  What RDF really does is;
>>> provide a data model agnostic 'layer for semantic connections across
>>> information resources'.
>> That is true, but I am hoping for a term that somehow also succinctly conveys
>> the **value proposition** of doing so -- i.e., a term that somehow alludes to
>> the benefit that this characteristic provides.
> I see the key value proposition is that is provides a semantically sound basis to combine data from different sources -- provided that the different sources use terms in consistent ways (i.e. satisfying the same semantic models).
> The core if this, IMO, is the semantic entailment associated with RDF graph merges, per the "Merging Lemma" in http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ (section 2 and appendix A).  (I just noticed this is omitted from the latest model theory - I assume it hasn't been invalidated by the changes.)

Yes and no. The new specs simply refuse to define a notion of entailment between *sets* of graphs and a graph. We had many debates about whether the merge or the union of a set of graphs best represented the same content as the 'combination' of them. (Unions treat shared bnodes as genuinely held in common between the graphs; merges do not.) Rather than try to resolve these debates, which seemed impossible, PFPS wisely suggested that we simply define entailment between graphs, and leave it to users to decide whether a set of graphs is best merged or unified (or indeed some combination of the two) into a single graph. 

So, the actual *content* expressed by the merging lemma is still true, but the way it is stated would need to be revized in the new semantics; and when you do that change, it becomes almost trivial. 

> It turns out, per a poster by Patel-Schneider and Haves presented at ISWC 2013 (http://iswc2013.semanticweb.org/content/posters/14) these core semantics are extremely weak.  IMO, that's a feature not a bug, if sufficient to allow graph merging without loss of corruption of meaning.

Yes indeed. No corruption is guaranteed; if you merge everywhere you might lose some content when bnodes are shared between the graphs being merged. Safer, IMO, to always take the union; but as I say, this is controversial. 


> #g
> --
>> David
>>> Cheers,
>>> Tim
>>> On Fri, Mar 7, 2014 at 1:20 PM, David Booth <david@dbooth.org
>>> <mailto:david@dbooth.org>> wrote:
>>>    I -- and I'm sure many others -- have struggled for years trying to
>>>    succinctly describe RDF's ability to allow multiple data models to
>>>    peacefully coexist, interconnected, in the same data.  For data
>>>    integration, this is a key strength of RDF that distinguishes it
>>>    from other information representation languages such as XML.   I
>>>    have tried various terms over the years -- most recently "schema
>>>    promiscuous" -- but have not yet found one that I think really nails
>>>    it, so I would love to get other people's thoughts.
>>>    This google doc lists several candidate terms, some pros and cons,
>>>    and allows you to indicate which ones you like best:
>>>    http://goo.gl/zrXQgj
>>>    Please have a look and indicate your favorite(s).  You may also add
>>>    more ideas and comments to it.  The document can be edited by anyone
>>>    with the URL.
>>>    Thanks!
>>>    David Booth
>>> --
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Received on Saturday, 8 March 2014 17:25:46 UTC

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