Re: Show me the money - (was Subjects as Literals)

[Jeremy Carroll]

 On 7/1/2010 8:44 PM, Pat Hayes wrote:
Jeremy, your argument is perfectly sound from your company's POV, but 
not from a broader perspective. Of course, any change will incur costs 
by those who have based their assumptions upon no change happening


I was asking for the economic benefit of the change, as opposed to the 
elegance benefit.
Personally, I am wholly convinced by the elegance argument - but it will 
not convince my management, nor should it.


I suspect there are several other companies and other open source 
activities that have investments that assume literals do not occur in 
subject position.


Elegance is not, IMO, a sufficient argument to negate those investments.
(The sort of thing we are talking about, is what sort of display is 
appropriate for a subject of a triple - we know that it is not a 
literal, so certain code paths, and options are not considered).


Of course, in an industrial consortium costs to one member maybe 
justified by benefits to another - but costs to any member do need to be 
offset by some benefit to some member ... I have yet to see much of an 
argument (Henry got a small bit of the way), that there are any such 
benefits (i.e. ones which have a dollar, euro or yuan value). I have 
pointed to dollar costs ... I expect to see some such benefit. I don't 
think that expectation is unreasonable, more a boundary that keeps 
people honest ... and not just indulging in an intellectual game (he 
says politely).


Jeremy

RE: Subjects as Literals, [was Re: The Ordered List Ontology]

[Michael Schneider]

On Behalf Of Nathan wrote on Friday, July 02:

>Pat Hayes wrote:
>> On Jul 1, 2010, at 11:18 AM, Yves Raimond wrote:
>>> "A literal may be the object of an RDF statement, but not the subject
>>> or the predicate."
>>
>> Just to clarify, this is a purely syntactic restriction. Allowing
>> literals in subject position would require **no change at all** to the
>> RDF semantics. (The non-normative inference rules for RDF and RDFS and
>> D-entailment given in the semantics document would need revision, but
>> they would then be simplified.)
>
>I have to wonder then, what can one all place in the s,p,o slots without
>changing the RDF semantics? literal and bnode predicates for instance?

Short answer: you can put URIs, literals and bNodes in all three positions
of a triple, without needing to touch the current RDF semantics spec. 

Longer answer:
 
The syntactic restrictions of RDF (no literal subjects, no literal or bnode
predicates) are not "checked" by the semantic conditions of the RDF
semantics. Every node in a triple is (in a first "step") simply related to
some resource in the interpreted universe. For URI nodes this is probably
clear, but even literals are meant to represent resources: all datavalues
are treated as resources in RDF! bNodes are a bit different, since they do
not stand directly for a specific resource, but indicate that some resource
/exists/. 

But, in the end, all you receive from the interpretation of all the nodes
occurring in an RDF triple is essentially a binary relationships between two
resources. And the rest of the semantics specification of RDF(S), and even
of OWL Full, works exclusively on these kinds of sets of binary
relationships, below the "syntax surface", so to speak. So the whole stack
of RDF-based semantics is ready to be used with "generalized" RDF out of the
box -- just waiting for the RDF syntax to give up its restrictiveness. :-)

As a special note: Even bNode predicates, and even literal predicates are
allowed in the RDF semantics and make sense (in a technical sense, at
least), because: 

  (a) Properties are also treated as regular resources by the RDF semantics.
They have some binary relation "attached" to them (in order to allow to use
them to relate two resources), but you can still treat them like any other
resource, e.g. relate themselves to another resource by some other
property).

  (b) Literals stand for data value resources, and nothing stops a data
value resource from being used as a predicate resource. (I leave it to the
philosophers here in the list to debate whether this is good use or bad use
in practice.) 

>variables or formulae as in n3?

For formulae: Certainly "no", since formulae are normally not interpreted to
denote resources, but are assertions being interpreted by a truth value. 

For variables: Firstly, /existentially/ quantified variables are already
treated, since they are represented by bNodes. Remains /universally/
quantified variables, as they exist in N3. Supporting them would definitely
need /some/ extension of the RDF semantics, since it has at least to be said
how such variables are interpreted (this is only said for URIs, plain and
typed literals, and for bNodes so far in the spec, see Sections 1.4 and 1.5
of the RDF Semantics [1]). I just cannot tell how much extension would be
required without more deeply thinking about it. So this question keeps open
from my side at the moment. Maybe Pat has an answer?
 
>read as: if a new serialization/syntax was defined for RDF what are the
>limitations for the values of node/object and relationship specified by
>the RDF Semantics?
>
>Best,
>
>Nathan
>
>ps: apologies if this is a dumb question, I fear i'd still be hear next
>year trying to answer it myself though ;)

Not dump at all. Technically pretty demanding, in fact.

Cheers,
Michael
 
[1] 

--
Dipl.-Inform. Michael Schneider
Research Scientist, Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: michael.schnei...@fzi.de
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===
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Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
===

RE: Show me the money - (was Subjects as Literals)

[Michael Schneider]

Henry Story wrote:

>So just as a matter of interest, imagine a new syntax came along that
>allowed literals in
>subject position, could you not write a serialiser for it that turned
>
>"123" length 3 .
>
>Into
>
>_:b owl:sameAs "123";
>   length 3.

But this is not an equivalent translation in RDF(S). 

The URI owl:sameAs has no specific meaning in RDF(S); you could likewise
write "ex:yz" instead. Only OWL tools, or at least RDF(S) tools with
additional support for owl:sameAs would be able to understand what you are
intending here. For other RDF tools, you are just asserting that there is
some resource with two properties, but the values of these two properties
are in no way related to each other -- quite in contrast to the original
triple.

So this should certainly not be suggested as "best practice" in an RDF
context.

Michael

--
Dipl.-Inform. Michael Schneider
Research Scientist, Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: michael.schnei...@fzi.de
WWW  : http://www.fzi.de/michael.schneider
===
FZI Forschungszentrum Informatik an der Universität Karlsruhe
Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
Tel.: +49-721-9654-0, Fax: +49-721-9654-959
Stiftung des bürgerlichen Rechts, Az 14-0563.1, RP Karlsruhe
Vorstand: Prof. Dr.-Ing. Rüdiger Dillmann, Dipl. Wi.-Ing. Michael Flor,
Prof. Dr. Dr. h.c. Wolffried Stucky, Prof. Dr. Rudi Studer
Vorsitzender des Kuratoriums: Ministerialdirigent Günther Leßnerkraus
===