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Re: Toward easier RDF: a proposal

From: Graham Klyne <gk@ninebynine.org>
Date: Mon, 26 Nov 2018 13:28:11 +0000
Message-ID: <5BFBF4EB.5040802@ninebynine.org>
To: Holger Knublauch <holger@topquadrant.com>, semantic-web@w3.org
On 22/11/2018 23:22, Holger Knublauch wrote:
> On 22/11/2018 10:21 PM, Graham Klyne wrote:
>
>> On 22/11/2018 00:38, Holger Knublauch wrote:
>>> Would you mind clarifying this statement a bit? What practical benefits would
>>> the foundation on formal logic add to a future (simplified) RDF, for average
>>> users? I have seen plenty of evidence that some aspects of the semantic
>>> technology stack are being regarded as too academic, and that the role of formal
>>> logic has been one driver of this detachment. Related topics are the
>>> non-unique-name-assumption and the open world assumption that are typically
>>> neither understood nor expected by average users.
>>
>> Jumping in, if I may...
>>
>> My view is that the formal logic underpinning of RDF serves (at least) one
>> important (and not-so-academic) purpose:
>>
>> Given two distinct RDF graphs that are taken to be descriptions of some world
>> or context, following the procedure of RDF graph merging guarantees that the
>> resulting graph is true of that world exactly when the individual graphs are
>> true of that world.
>
> Sorry, I cannot follow this explanation. What do you mean with a graph being
> true of a world? Could you maybe give a practical example?

The obvious example is being true of the real world we live in - the phrasing 
was just intended to allow for RDF use describing fictional or potential worlds.

So, to take an excerpt from TimBL's FOAF profile at [1]:

[[
     <rdf:Description 
rdf:about="http://www4.wiwiss.fu-berlin.de/booksMeshup/books/006251587X">
         <dc:creator rdf:resource="http://www.w3.org/People/Berners-Lee/card#i"/>
         <dc:title>Weaving the Web: The Original Design and Ultimate Destiny of 
the World Wide Web</dc:title>
     </rdf:Description>
]]
-- [1] http://dig.csail.mit.edu/2008/webdav/timbl/foaf.rdf

We may have some common understanding that the URIs 
http://www4.wiwiss.fu-berlin.de/booksMeshup/books/006251587X, 
http://www.w3.org/People/Berners-Lee/card#i, dc:creator and dc:title refer to a 
book, a person and two RDF properties respectively, and that under that 
understanding they describe a true statement about authorship of a book with a 
given title.

Without this understanding, maybe the URIs can be interpreted as referring to, 
say, a declaration of intent and a megalomaniac spider, etc.  The graph might be 
true of this world too.

But we don't need to know any of this to combine the graph at from [1] with a 
graph from another source that may use some of the same URIs.  As long as the 
interpretation of all the URIs used is consistent, and both graphs make 
statements that are true under that interpretation, then the resulting combined 
graph (constructed according to the rules of RDF graph merging) is also true.

This ability to combine independent graphs is, to my mind, is what RDF semantics 
gives us (while remaining completely agnostic about what the URIs actually 
denote).  It's not something that concerns us much in day-to-day work with RDF, 
but I feel that the semantics provide an important underpinning for some of the 
things that we wish to do with RDF.

>>
>> To my mind, this underpins the (open-world?) idea of being able to
>> meaningfully combine RDF information from independent sources. (Without
>> implying any guarantee of absolute truth, whatever that may be.)
>
> In my viewpoint, an RDF graph is primarily a data structure - a set of triples.
> Combining RDF triples produces another data structure as the union of these
> triples.  That's it.

If that's all it is, I think it has less real value than we like to think.  What 
makes it better than XML or JSON or any other data structure with some plausible 
merging rules?

I perceive the notion of permissionless innovation around RDF data depends on 
being to bring data together from independent sources, without requiring 
specific agreement by every party about what all the terms mean, while providing 
a guarantee that intended meanings are maintained.

> ... BTW neither SPARQL nor Turtle nor many other RDF-based
> standards require "open world", so this interpretation could be made entirely
> optional.

Sure, not required.  But in locally closed contexts, I find it hard to see why 
RDF is significantly better than the other formats and tools that many 
developers prefer to work with.  Even if much (or even most) use of RDF is in 
locally closed contexts, I feel that what sets it apart is the capability to be 
used dependably across contexts in which the assumed knowledge does not entirely 
overlap.

(Many years ago, Dan Brickley used the phrase "missing isn't broken" [citation 
lost], which has stuck with me as a key differentiator for RDF.  I perceive this 
idea as being underpinned by RDF's formal semantics that allow it to be 
interpreted consistently with varying levels of knowledge about the world.)

#g
--
Received on Monday, 26 November 2018 13:28:37 UTC

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