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Re: RDF* semantics

From: Olaf Hartig <olaf.hartig@liu.se>
Date: Sat, 17 Aug 2019 15:49:15 +0000
To: "public-rdf-star@w3.org" <public-rdf-star@w3.org>
CC: Kingsley Idehen <kidehen@openlinksw.com>
Message-ID: <2369041.MCJSzTz68t@porty3>
Kingsley,

On onsdag 14 augusti 2019 kl. 11:01:19 CEST Kingsley Idehen wrote:
> [...]
> >> It states that a Person named "Alice" :claims a Person named "Bob" has
> >> age 23 expressed as in integer.
> > 
> > I disagree. It states that a Person named "Alice" :claims something and
> > this something is of rdf:type foaf:Person. So, what she is claiming is a
> > person rather than being about a person.
> 
> I hope you are not interpreting :clams somewhat whimsically, since I
> didn't actually assert that the rdfs:range of :claims is an
> rdf:Statement instance in my original example sentence.

I know. That's why I am saying that, according to your example data, what 
Alice is claiming is a person (something of type foaf:Person) rather than a 
statement about the person. Let's break down your Turtle-formatted example 
data by writing it in Turtle *without* the syntactic abbreviations of Turtle 
that you have been using, which gives us the following snippet of Turtle:

_:b1  rdf:type  foaf:Person .
_:b1  foaf:name  "Alice" .
_:b1  :claims  _:b2 .
_:b2  rdf:type  foaf:Person .
_:b2  foaf:name  "Bob" .
_:b2  foaf:age "23"^^xsd:integer .

As I hope you see now, there is some thing--denoted by blank note _:b2--that 
the person Alice :claims and this thing is of rdf:type foaf :Person. So, 
according to this data, Alice claims a person. That's different from what was 
meant to be captured in my original example, namely, that Alice makes a claim/
statement *about* a person (in my original words: "we my want to capture that 
Alice told us that Bob's age is 23, even if we don't have a document from 
Alice with this statement/claim regarding Bob's age").

> [...]
> BTW -- I can also do all of this in a document (as per SPARQL Named
> Graphs) and just pepper the document with additional metadata for
> provenance purposes. Basically, why aren't  SPARQL Named Graphs a viable
> solution to this problem i.e., RDF stays as is for data definition while
> languages such as SPARQL handle operations on RDF structured data?

I never said that Named Graphs cannot be used as a solution (to the problem of 
representing and querying metadata about individual triples). In contrast, 
such an application of the concept of Named Graphs may be defined by assuming 
that every relevant Named Graph consists of a single triple only. However, by 
using the concept of Named Graphs to capture triple-level metadata, it becomes 
tricky to also represent and query graph-level metadata. More precisely, it 
becomes tricky to represent both triple-level metadata and graph-level 
metadata within the same dataset; and it becomes tricky to request both 
triple-level and graph-level metadata within the same query.

Olaf


> >> [...]
> >> 
> >>> I guess what you actually wanted to write was something
> >>> like the following:
> >>> 
> >>> [ a foaf:Person; foaf:name "Alice"]
> >>> 
> >>>            :claims [ a rdf:Statement ;
> >>>            :
> >>>                      rdf:subject   :Bob ;
> >>>                      rdf:predicate foaf:age ;
> >>>                      rdf:object    "23"^^xsd:integer ] .
> >> 
> >> No, that is just a reified version of my initial statement.
> > 
> > Are you saying that you consider the set of triples serialized as this
> > piece of Turtle to be semantically equivalent to the set of triples
> > serialized in the piece of Turtle above?
> 
> Of course not.
> 
> 
> Kingsley
> 
> >> [...]
> >> 
> >>> By the definition of the RDF* data model, every RDF graph is an RDF*
> >>> graph. Additionally, by the definition of the RDF*-to-RDF mapping, every
> >>> RDF* graph can be viewed as an RDF graph.
> >> 
> >> Sorta, but this is serious work to be done explaining all of this in a
> >> manner that prevents the confusion I fear.
> > 
> > Point taken.
> > 
> > Olaf


Received on Saturday, 17 August 2019 15:49:44 UTC

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