Re: Terminology: How to call "IRI or blank node"?

The danger is that one talks about a node when one means to talk about a 
resource, or vice versa.  This can be benign, if the misconception either is 
not important or can be easily fixed, or serious, if the misconception matters 
and is not easy to fix.

When one is writing specifications, the only safe assumption is that 
misconceptions are matter and are not easy to fix, because one does not know 
the contexts in which one's terminology will be used.

peter



On 12/22/2014 04:59 PM, Irene Polikoff wrote:
> So, let's say there is a theory and meta theory and even several layers of it. There used to be a joke slogan in the OO community, btw, "Anything you can do, I can do meta". And let's say, these get conflated.
>
> Who and what will such conflation impact negatively? What systems and applications get broken? How will it change what people who are using the standards to build solutions are doing and how they are putting the technologies to work?
>
> In other words why is this important and what parts are important?
>
> Irene
>
> Sent from my iPhone
>
>> On Dec 22, 2014, at 12:28 PM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com> wrote:
>>
>> Being the same is a concept that needs clarification here.
>>
>> Yes, "2"^^xs:integer is a literal and ex:two is a URI.  These cannot be the same in RDF because URIs, blank nodes, literals are disjoint.  However, ex:two can be required to denote an integer, which is a literal value.
>>
>> Yes, there is no atomic name in the metatheory of RDF that stands for those nodes in an RDF graph that can be the subject of a triple in an RDF graph. But why does there have to be?  One can always say "IRI or blank node".
>>
>> One could create such an atomic name.  One might use "entity" for this purpose.  However, one should *not* use rdf:Entity, as that would conflate the RDF theory (where one has names like rdf:Property, rdfs:Resource, and xs:Integer) and the RDF metatheory (where one has names like resource, RDF graph, IRI, and property).   Well, if rdf:Entity was not an IRI, then there might not be a conflation, but there would be other problems.
>>
>>
>>
>>
>> peter
>>
>>
>>
>>
>>> On 12/22/2014 07:49 AM, Irene Polikoff wrote:
>>> At some point in the discussion we have agreed not to talk about resources when discussing RDF graphs and, instead, talk about nodes.
>>>
>>> I am talking about literal nodes.
>>>
>>> Given the following triples
>>>
>>> ex:house ex:number "2"^^xs:integer
>>> ex:two rdf:type xsd:Integer
>>> ex:house ex:number ex:two
>>>
>>> There will be two different nodes for the number 2. The first one is the literal node. The second one is an IRI node. They will never be the same and the graph represented by the first triple is not the same graph as the graph represented by the two last triples.
>>>
>>> The fact that ex:two may stand for the "real world" resource that philosophically is the same is irrelevant here as we are talking about data structures and their processing.
>>>
>>> The vocabulary term that is missing is the one that identifies RDF terms that can be subjects of a triple. In the context of this working group, this is an important concept that needs its own name. I propose rdf:Entity.
>>>
>>> Irene
>>>
>>>
>>> Sent from my iPhone
>>>
>>>> On Dec 22, 2014, at 10:10 AM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com> wrote:
>>>>
>>>> There are a number of intertwined issues here.
>>>>
>>>> Are literal values resources in RDF?  Yes, a literal value (e.g., the number 2) is a resource.  This is just abiding by the principles of resources in the Semantic Web.
>>>>
>>>> Can literal values have property values in RDF?  Yes, a literal value (e.g., the number 2) can have property values.
>>>>
>>>> Can URIs denote literal values in RDF?  Yes, a URI (e.g., ex:two) can denote a literal value (e.g., the number 2).  This is just abiding by the principles of IRIs in the Semantic Web.
>>>>
>>>> Is it possible in RDFS to make a URI to denote a literal value without causing a contradiction?  Yes, via something like  ex:two rdf:type xsd:Integer.
>>>>
>>>> Is it possible in RDFS to state that some literal value has a property value without causing a contradiction?  Yes, via something like ex:two rdf:type xsd:Integer. ex:two ex:prime xsd:true.
>>>>
>>>> Is it possible in RDFS to directly state that a particular literal value has a property value?  No, because literals cannot be the subject of RDF triples.
>>>>
>>>> Is it possible in RDF to get close to stating that a particular literal value has a property value?  Yes, you can use reification as in  _:a rdf:subject 2. _:a rdf:predicate ex:prime. _:a rdf:object xsd:true.
>>>>
>>>> peter
>>>>
>>>>
>>>>> On 12/22/2014 06:39 AM, Irene Polikoff wrote:
>>>>> RDF specification clearly says that there are 3 types of RDF nodes: IRI, blank node and literal. Each has its own unique/different characteristics including, for example, that literal can only be an object of a triple and blank node can't be a predicate of a triple.
>>>>>
>>>>> I believe the specification makes it clear that these  three node types are disjoint. Thus, ex:two can not be a literal node as it is an IRI. I also thought we were discussing here RDF nodes, not abstract concepts of literals.
>>>>>
>>>>> I remember hearing that there were some discussions in the RDF working group about letting literals be subjects, but this proposal was rejected, wasn't it?
>>>>>
>>>>> Irene
>>>>>
>>>>> Sent from my iPhone
>>>>>
>>>>>> On Dec 22, 2014, at 8:49 AM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>> On 12/22/2014 01:45 AM, ☮ elf Pavlik ☮ wrote:
>>>>>>>> On 12/21/2014 01:38 AM, Peter F. Patel-Schneider wrote:
>>>>>>>> In RDF all resources can have property values, even literal values.
>>>>>>>>
>>>>>>>> peter
>>>>>>> Hi Peter :)
>>>>>>>
>>>>>>> Could you please explain it little more and if possible share links to
>>>>>>> relevant references?
>>>>>>>
>>>>>>> Thanks!
>>>>>>
>>>>>> The original version of RDF, as described in the RDF Model and Syntax Specification http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/, talks about Resources and Literals, but does not indicate directly whether they are disjoint.  However, there is already the idea that anything is a resource and that anything can described by a URI.  See Section 2
>>>>>> http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/#basic and Section 5 http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/#model for more information.
>>>>>>
>>>>>> The original version of RDFS, http://www.w3.org/TR/1998/WD-rdf-schema/, which never became a full W3C recommendation, has the initial class hierarchy, including rdfs:Resource, rdfs:Literal, rdfs:Class, and rdf:Property in Figure 2.   In this figure, rdfs:Resource is the universal class, with rdfs:Class, rdf:Property, and rdfs:Literal all as subclasses.  Here is the first direct requirement that literal values are resources.
>>>>>>
>>>>>> The first formal treatment of RDF is in RDF Semantics http://www.w3.org/TR/2004/REC-rdf-mt-20040210/.  Here interpretations for RDF are first defined, in Section 1.3 http://www.w3.org/TR/2004/REC-rdf-mt-20040210/#interp, with the domain of an interpretation being the set of resources and a subset of the resources being literal values, as in the original version of RDFS.  Properties are another subset of the resources, which are linked to their extent, which is a set of pairs over the resources.  There is no requirement here that literals cannot be the first element of a property pair.
>>>>>>
>>>>>>
>>>>>> One might argue that the formal treatment is a misreading of the informal 1999 description of RDF, but the ability for literals to have property values has definitely been in RDF since at least 2004.  This stance is also consistent with the dictum that URIs can identify anything, which includes literal values.
>>>>>>
>>>>>> For example, one can say in RDF
>>>>>>
>>>>>> ex:two rdf:type xsd:Integer .
>>>>>> ex:two ex:prime xsd:true .
>>>>>>
>>>>>>
>>>>>> Peter F. Patel-Schneider
>>>>>> Nuance Communications
>>>>>>

Received on Tuesday, 23 December 2014 01:31:35 UTC