[foaf-dev] [foaf-protocols] revisiting FOAF project goals

Dave Brondsema dave at brondsema.net
Thu Jun 25 19:08:11 CEST 2009

Matthew Rowe wrote:
> Hi Olaf
> Thanks for the comments.
> On 25 Jun 2009, at 06:14, Olaf Hartig wrote:
>> Hey Matthew,
>> On Wed Jun 24 14:37:39 CEST 2009 Matthew Rowe wrote:
>>> On 24 Jun 2009, at 12:40, Melvin Carvalho wrote:
>>> [...]
>>>> Perhaps named graphs can help, or maybe storing an extra field in  
>>>> a DB
>>>> for the weighting?
>>> Yeh this is something I have been puzzled by aswell. Olaf Hartig's
>>> paper on "Querying trust in RDF data with rSPARQL" [1] details that
>>> RDF graphs can be trust weighted, and expresses individual statements
>>> within the RDF graph as having trust values (ranging from 0-1).
>>> However, the paper does not explicitly say how trust values would be
>>> stored (ie. what the semantics would be for expressing a trust  
>>> value).
>>> As you suggested it appears that the db contains an associated trust
>>> value with a given triple. I assume that in terms of assigning trust
>>> values to relationships, trust values would be assigned to the
>>> relationship triple:
>>> (<#Alice> foaf:knows <#Bob>) 0.9
>> Just to make this clear, my trust values represent the  
>> trustworthiness of RDF
>> statements. There is a difference to trust values that represent the
>> trustworthiness of persons. You should not confuse both. If you want  
>> to
>> represent the trust value associated with the relationship between  
>> persons
>> you must not assign a trust value to the relationship triple (as you
>> suggest). Associating 0.9 to the triple
>> :Alice foaf:knows :Bob
> Granted, that was just a naive example I was using but I see your point.
>> means the statement that "Alice knows Bob" can be trusted to a high  
>> degree
>> (considering a trust value of 1.0 is the upper bound). It does not  
>> mean that
>> Alice highly trusts Bob.
>> BTW - Intentionally, I do not write about storing trust values (of
>> statements!) in my paper because I assume in the majority of cases  
>> these
>> values do not have to be materialized. Usually, the trustworthiness of
>> processed statements is determined on demand; i.e. when it is needed  
>> in the
>> application (or in the query engine in my case). At best these  
>> values are
>> cached for a while. I don't see no value in explicitly describing  
>> them with
>> RDF.
>> However, for the unlikely requirement to materialize trust values  
>> determined
>> for statements (i.e. to explicitly describe the trustworthiness of  
>> statements
>> with RDF) I developed a vocabulary [1]. This approach is based on RDF
>> reification.
>> In contrast to trust values for statements I think it is reasonable to
>> explicitly represent the trust values for persons (i.e. describe  
>> these values
>> with RDF). That's what you want to do, right? My vocabulary may be  
>> used for
>> this, too. Notice, in this case you don't need no reification. For  
>> example,
>> the statement Alice trusts Bob with trust value 0.9 can be described  
>> as
>> follows:
>> :Bob tv:trustworthiness [ rdf:type tv:TrustValue ;
>>                                       rdfs:value 0.9 ;
>>                                       tv:truster :Alice ]
> I like this form but I think there is an issue about how different  
> people interpret trust. From a philosophical perspective when we say  
> that we trust someone:
> Do we simply trust someone in general? i.e. In the broad sense of the  
> term? Alice trusts Bob
> or
> Do we trust a person given a context? i.e. Alice trust Bob's opinion  
> on the Semantic Web
> I am more inclined to say the latter. Is there are any way this could  
> be included in your vocabulary as something like:
> Bob: tv:trustworthiness [rdf:type tv:TrustValue;
> 					rdfs:value 0.9 ;
> 					tv:truster :Alice;
> 					tv:context <http://dbpedia.org/resource/Semantic_Web> ]

With Konfidi's vocabulary http://www.konfidi.org/ns/trust/1.2# I do:

[ a k:Relationship ;
    k:truster <http://brondsema.net/dave#> ;
    k:trusted _:andy ;
    k:about [ a k:Item ;
        k:topic ktopic:internet-communication ;
        k:rating 0.95

That is more similar to the ontology Melvin mentioned.

Dave Brondsema : dave at brondsema.net
http://www.brondsema.net : personal
http://www.splike.com : programming

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