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Re: Signal for semantic extensions

From: Sandro Hawke <sandro@w3.org>
Date: Sat, 18 May 2013 10:46:08 -0400
To: Richard Cyganiak <richard@cyganiak.de>,David Booth <david@dbooth.org>
CC: public-rdf-comments <public-rdf-comments@w3.org>
Message-ID: <197706bc-17dd-47e2-9400-6e888fad05c2@email.android.com>


Richard Cyganiak <richard@cyganiak.de> wrote:

>David,
>
>(Unofficial response to ask for clarification)
>
>Given that any RDF vocabulary is a semantic extension, isn't the answer
>here simply that if a client sees a class or property IRI that it
>doesn't know, then it must assume that additional inferences are
>possible?
>

+1

It may turn out in some cases that consumers can inspect (including dereference) unknown terms and learn what inferences are possible.   That would be nice, but I don't think we quite know how to do that with a guarantee of completeness yet.

I'd probably argue against a 'requires' thing as too error prone and not really necessary.

   - Sandro

>Richard
>
>
>On 18 May 2013, at 04:05, David Booth <david@dbooth.org> wrote:
>
>> This comment raises an issue that is somewhat theoretical at present.
>I mentioned it over a year ago (message below) but have not seen any
>discussion about it.  I have not seen it be a problem in practice yet,
>so I do not think it is urgent for the working group to address.  But
>if RDF gains popularity over the coming years, and more semantic
>extensions are introduced, it could become a practical consideration,
>given the long time span between RDF versions.
>> 
>> At present there is no standard way in RDF to unambiguously signal
>the expectation of a particular semantic extension.  I'll explain
>further what I mean, and make a specific proposal.  Perhaps others will
>think of a better way to solve the problem, but hopefully this will at
>least explain what it is.
>> 
>> Suppose an RDF consumer receives a graph written by an RDF author and
>(roughly speaking) the RDF consumer wants to be able to fully
>"understand the author's intended meaning" of that graph.  More
>precisely, the RDF author has used certain semantic extensions that
>imply certain entailments, and wishes to allow consumers of that graph
>to be able to automatically (by machine) determine these entailments.
>In turn, the RDF consumer wishes to be able to compute all of those
>entailments.  Note that this is *not* suggesting that the RDF consumer
>be *required* to compute the RDF author's intended entailments.  It is
>only about *enabling* the RDF consumer to do so if desired.
>> 
>> For semantic extensions that are well known, such as OWL, the RDF
>consumer can detect the presence of well known URIs (such as OWL
>predicates) to know that those well known semantic extensions are
>intended.  But for semantic extensions that are *not* well know --
>non-standard semantic extensions -- the RDF consumer has no standard
>automatable way to know that certain URIs are intended to signal the
>use of particular semantic extensions.  Thus, the RDF consumer has no
>standard way of determining whether or not he/she/it has computed all
>of the entailments that the RDF author intended to convey.
>> 
>> When the RDF consumer processes an RDF graph, the processor should be
>able to clearly indicate to the user either: "I have computed all of
>the author's intended entailments" or "I cannot compute all of the
>author's intended entailments because I do not have the module for
>semantic extension 'http://example/BobsFavoriteExtension'.  Please load
>it and try again."  But this is only possible if the RDF author has an
>unambiguous standard way to signal the intended semantic extensions.
>> 
>> The motivation for this use case is to enable the vision of the
>semantic web to work, even in the presence of new semantic extensions. 
>This means that: (a) the RDF consumer cannot be expected to have any
>other communication with the RDF author (other than obtaining the graph
>that the author had provided); and (b) the RDF consumer must be able to
>perform these steps automatically (by machine).
>> 
>> I suggest the RDF working group define a standard predicate
>rdf:requires (or whatever name the group chooses) that an RDF author
>can use to indicate that a particular semantic extension is intended. 
>It could be used like this:
>> 
>> <> rdf:requires <http://example/BobsFavoriteExtension> .
>> 
>> which would indicate that the current document uses semantic
>extension <http://example/BobsFavoriteExtension> .  Hence, to be
>assured of determining all of the document author's intended
>entailments, the RDF processor must understand that semantic extension.
>> 
>> Furthermore, for backward compatibility with OWL, it would be good to
>define:
>> 
>>  owl:imports rdfs:subPropertyOf rdf:semanticExtension .
>> 
>> and recommend that RDF processors also recognize owl:imports as
>signaling a semantic extension.
>> 
>> Again, since I have not yet seen this issue arise in practice, I
>would consider it a low priority to fix, and would not mind if the
>working group decides to defer it to a future RDF version.  On the
>other hand, it is a very easy gap to fix.
>> 
>> Thanks,
>> David
>> 
>> 
>> On 03/30/2012 06:18 PM, David Booth wrote:
>>> -------- Forwarded Message --------
>>> From: David Booth <david@dbooth.org>
>>> To: Pat Hayes <phayes@ihmc.us>
>>> Cc: Jonathan A Rees <rees@mumble.net>, Jeni Tennison
>>> <jeni@jenitennison.com>, www-tag@w3.org List <www-tag@w3.org>
>>> Subject: Re: The TAG Member's Guide to ISSUE-57 Discussion - F2F
>reading
>>> Date: Fri, 30 Mar 2012 18:17:06 -0400
>>> 
>>> Hi Pat,
>>> 
>>> On Wed, 2012-03-28 at 14:24 -0500, Pat Hayes wrote:
>>>> FWIW, I am willing to work actively (on- or off-list) with anyone
>who
>>>> wants to try reconciling any proposal with the RDF semantics, or
>just
>>>> to explore any semantic issues. This is particularly timely as the
>>>> RDF2 WG is right now debating issues which impinge on the RDF
>>>> semantics framework, so it would be good to get any pending issues
>or
>>>> problems out into the open.
>>> 
>>> I would suggest that the RDF WG look at Part 3 "Determining Resource
>>> Identity" of "Resource Identity and Semantic Extensions: Making
>Sense of
>>> Ambiguity":
>>> http://dbooth.org/2010/ambiguity/paper.html#part3
>>> That section proposes a standard process for determining resource
>>> identity.  As far as I know, I did not invent this process.  I
>simply
>>> documented what seemed to be the general ideas floating around.
>>> 
>>> However, I did identify one specific gap in the RDF specs:
>>> [[
>>> At present there is a minor gap in the RDF standards, in that there
>is
>>> no standard way for an RDF processor to recognize that a particular
>URI
>>> is intended to signal an opaque semantic extension: the knowledge of
>>> which URIs are intended to signal opaque semantic extensions must be
>>> externally supplied to the RDF processor.  The RDF processor must
>>> magically know about them in advance.  It cannot alert the user to
>the
>>> need for a new opaque semantic extension that was previously
>unknown.
>>> This gap could be addressed by defining a standard predicate, such
>as
>>> rdf2:requires, to explicitly indicate when a particular semantic
>>> extension is required.  However, since it currently seems unlikely
>that
>>> many semantic extensions will be needed that cannot be defined using
>>> standard inference rules, this does not seem like a major gap.
>>> ]]
>>> 
>>> I will forward this message separately to the RDF comments list,
>since I
>>> cannot post to the regular RDF list.
>> 

-- 
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Received on Saturday, 18 May 2013 14:46:07 UTC

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