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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Real-world trust policies
Vinicius AlmendraDaniel Schwabe
Dept. of Informatics, PUC-RioISWC’05
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Agenda
Problem Statement What Does Trust Mean? The Trust Model Building Real-world Trust Policies An Example Future Work Conclusions
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Problem Statement
Scenario: collection of semantic web dataThrough exchange: P2P networks,
semantic social desktopsThrough web navigation: Piggy
Bank-like approaches Problem: is this information
trustful?
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
What Does Trust Mean?
Using a real-world model of trust: “trust is reliance on received information” (Gerck, 1998)
To trust someone or something => To rely on it to achieve some goal Reliance on a banking Website to move
money Reliance on a car or plane while doing a
trip Reliance on a statistical software
Reliance implies an action (actual or future) – boolean value
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Reliance
Reliance is NOT Blind Static Irrevocable
Reliance depends on Reasoning Circumstances Beliefs Freedom
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
What Does Trust Mean?
Reliance is useful because It gives a mental frame to think about
trustfulness It links trust with action, while keeping them
apart Why real-world trust?
The model is being built in order to support an easy mapping from daily trust decisions to a computable representation
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
The Trust Model
To trust is to virtually rely Trust is subjective: it depends on who
trusts, the trusting agent Object of trust: facts
Statements about reality Facts can be just known (asserted) and
can also be trusted. Trust decision: happens when the trusting
agent decides that an asserted fact can be trusted
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
The Trust Model
Trust decision must be reasonable: there must be a justification for accepting that a fact is trustful
Justification is based on beliefs, which are grounded on trusted facts
A trust policy is a set of rules that the trust agent uses to deduce the trustfulness of a fact. It is associated with a goal
Trust policies should be built incrementally
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Trust policies Answer the question: “is this fact trustful?” Reasoning behind a trust decision can be expressed
using classic logic Trust policy = predicate over a fact asserting its
trustfulness Fact = (s,p,o,c) – subject, predicate, object and
context Reasoning about trusted facts May use the domain theory of the agent Example: “I trust that a person A is a friend of a
person B when A is my friend and B is known to be a person”
),'','',(),,'','('
)'',(),,,(
cPersontypeottrustedFaccsfriendmettrustedFac
friendpequalcopsP
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Trust Policies
If the facts below were trusted: (‘Me’, ‘friend’, ‘John’, ‘My context’) (‘Erick’, ‘type’, ‘Person’, ‘My context’)
This fact would be trusted (‘John’, ‘friend’, ‘Erick’, ‘My context’)
But not these one (‘Mary’, ‘friend’, ‘John’, ‘Mary’s context’) (‘John’, ‘brother’, ‘Erick’, ‘Robert’s context’)
),'','',(),,'','('
)'',(),,,(
cPersontypeottrustedFaccsfriendmettrustedFac
friendpequalcopsP
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Trust Policies
Trust axiom Given a fact (s,p,o,c) Given a trust policy P
),,,(),,,(),,,(
copsPcopsctassertedFacopsttrustedFac
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Trust Policies
Trust Policies can be combined through aggregation (union of trustful facts) or specialization (intersection of trusted facts)
),,,(),,,(),,,(
),,,(),,,(),,,(),,,(
321
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copsPcopsPcopsP
copsPcopsPcopsPcopsP
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Scenario: a person looking for trustful news-related information
We start with three policies: Self-trust: trust everything contained in “my” context
Context info: trust everything stated about a context
Good News: trust news that come from friends
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Policies described as Prolog clauses:trustedFact(S,P,O,C) :-
assertedFact(S,P,O,C),goodNewsRelatedInfo(S,P,O,C).
goodNewsRelatedInfo(S,P,O,C) :-selfTrust(S,P,O,C).
goodNewsRelatedInfo(C,_,_,C).
goodNewsRelatedInfo(S,P,O,C) :- goodNews(S,P,O,C).
goodNews(_,rdf:type, 'news:News' ,C) :-trustedFact(C, dc:creator, Friend, _),trustedFact(myself, foaf:knows, Friend, my_context).
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsI foaf:knows John (my context)
Self-trustContext infoGood news
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsI foaf:knows John (my context)
Self-trustContext infoGood news
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsSelf-trustContext infoGood news
I foaf:knows John (my context)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsemail_mary dc:creator Mary (email_mary)
Self-trustContext infoGood news
I foaf:knows John (my context)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsemail_mary dc:creator Mary (email_mary)
Self-trustContext infoGood news
I foaf:knows John (my context)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsSelf-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsFootball_news rdf:type news:News (email_mary)
Self-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsFootball_news rdf:type news:News (email_mary)
Football_news dc:description ‘Brazil World Cup champ’ (email_mary)’
Self-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsFootball_news rdf:type news:News (email_mary)
Football_news dc:description ‘Brazil World Cup champ’ (email_mary)’
I foaf:knows mary (my context)
Self-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsFootball_news rdf:type news:News (email_mary)
Football_news dc:description ‘Brazil World Cup champ’ (email_mary)’
I foaf:knows mary (my context)
Self-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsFootball_news rdf:type news:News (email_mary)
Football_news dc:description ‘Brazil World Cup champ’ (email_mary)’
Self-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
I foaf:knows mary (my context)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsFootball_news dc:description ‘Brazil World Cup champ’ (email_mary)’
Self-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)
I foaf:knows mary (my context)
Football_news rdf:type news:News (email_mary)
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
An Example – Trust in News Info
Asserted facts Trust policies Trusted factsSelf-trustContext infoGood news
I foaf:knows John (my context)email_mary dc:creator Mary (email_mary)I foaf:knows mary (my context)Football_news rdf:type news:News (email_mary)Football_news dc:description ‘Brazil World Cup champ’ (email_mary)’
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Implementation
A first implementation was done using named graphs
We moved to logic programs (XSB Prolog) to better represent trust policies
Next step: link these logic programs with a RDF triple store.
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© 2005, Daniel Schwabe. Vinicius Almendra – SWPW – ISWC05
Conclusions and Future Work
Simple approach promising Ongoing work
Handling negation – could be pushed to the underlying KB
Adding support to inference – to take advantage of the domain knowledge
Linking with RDF triple stores Providing a method to build trust policies
that keeps “real-world” property Build to help users specify policies Apply to realistic case study
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