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Re: Signal for semantic extensions

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sat, 18 May 2013 10:01:38 +0100
Message-Id: <6CDCFD15-F8CA-45D2-BD25-36046C47E9F9@cyganiak.de>
Cc: public-rdf-comments <public-rdf-comments@w3.org>
To: David Booth <david@dbooth.org>

(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?


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.
Received on Saturday, 18 May 2013 09:02:06 UTC

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