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

Peter Ansell ansell.peter at gmail.com
Thu Jun 25 23:51:32 CEST 2009

Accidentally sent off-list reply...

---------- Forwarded message ----------
From: Peter Ansell <ansell.peter at gmail.com>
Date: 2009/6/26
Subject: Re: [foaf-dev] [foaf-protocols] revisiting FOAF project goals
To: Dave Brondsema <dave at brondsema.net>

2009/6/26 Dave Brondsema <dave at brondsema.net>:
> 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
>    ]
> ].

If you assume that people will create a single relationship for each
trusted topic it could be much simpler than that.

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

Relying on people understanding the completely abstract k:about and
k:Item isn't useful if they can just as easily create the relationship
with a single level of structure and have the same functionality in
the end.



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