TPS T rust and P rovenance in S weto
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Transcript of TPS T rust and P rovenance in S weto
TPSTrust and Provenance in Sweto
Meenakshi Nagarajan
Willie Milnor
Nicole Oldham
Introduction
Nature of the Semantic Web Machine understandable informationOpen, distributed, low barriers with publicationNew techniques to validate information
Provenance is key to establishing trust in the information
Not adequate to associate trust in the content of the source
Unreasonable to know trust in every statement by verifying provenance and source
Option1: Associate a trust value with every sourceCNN = 0.9
Counter-Intuitive to how we process informationStatement about “War in Iraq” and “The Iraqi
People’s leader” made by CNN and Iraq Daily.
Option 2: May be, a trust value for every source for every domain under consideration Infinite domains and sources – not scalable
Option 3: Possibility of finite users ascertaining their
confidence in some statementsTrust anyone has on a statement as a
function of their trust on the user who placed a confidence on this statement
Very close to humans analyze content to ascertain credibility
Recommendation systems, e-Bay etc TPS
Trust a member of a network can associate with a statement on the Semantic Web is proportional to the belief asserted on the statement by some user (also in the network) and the trust the member has on this user.
statement
User
have beliefs in
truststrusts
trusts
trusts
Belief in statement
trusts
Ux
trusts
trusts
Based on this..
We identified the requirement of two modelsProvenance model (essentially Sweto itself)
Provenance information of statements
Trust model Trust between users who placed a confidence
value in a statement in Sweto
Related Work Knowledge management to determine the
validity and origin of information on the web http://www.eil.utoronto.ca/km/papers/fox-kp1.pdf
Proof-like support system for explaining provenance informationhttp://www.ksl.stanford.edu/people/pp/papers/PinheirodaSilva_DEBULL_2003.pdf
Role of trust in ascertaining credibility of information – Web of trusthttp://www.cs.washington.edu/homes/pedrod/papers/iswc03.pdf
A framework for trust propagation using notions of trust and distrust in a web of trust – e-commerce systemshttp://tap.stanford.edu/trust04.pdf
Issues related to using trust in web based social networks, specifically in building and maintaining a trust network on the web http://trust.mindswap.org/
Combining trust and provenancehttp://ebiquity.umbc.edu/v2.1/_file_directory_/resources/58.pdf
The Models ..
Provenance Model – enhancing SwetoCaptures
Provenance information of statements in Sweto Confidence / truth value of a statement User who placed that confidence / truth value
The Models ..
Trust Model WOTCaptures
Trust between users, where a user E users who entered a confidence / truth value in a statement
When a user enters a confidence / truth value into the provenance model, he is
Added to the provenance model Optionally, he could add himself to the WOT if he wishes
to place trust values in other users
Placing trust in other users of the WOT intuitively, user1 verifies the confidence value
placed by userx in the statementDepending on the confidence values, user1
establishes trust in userx
A BIG ASSUMPTION
ALL USERS ARE BASICALLY TRUSTWORTHY AS FAR AS GOING THROUGH THE PROCESS OF ENTERING TRUTH AND TRUST VALUES
Unique features and contribution
Features Source and domain consideration. No single source,
single trust value concept Personalized trust metrics for every user in the
system – respecting the subjective nature of trust Adaptive model
Ability to change trust in users and/or truth values on statements
Immediately reflects on results obtained
Aggregation in TPS
Primary Question we are trying to answer How much can I trust an association I get
from Sweto ? Can also answer
How much do I trust user x ? (directly or through propagation of trust / distrust)
Web Of Trust A directed Graph of users of the system with edge
weights as the trust values between them.
Every user who places a truth value in an assertion is represented as a node in this graph.
A
B
E
C
D
F
0.7
0.2
0
1.0
0.6
0.7
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0.4
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Representation of Trust in the WOT
A matrix that contains the actual trust values that each of the n users placed in any of the other users is maintained.
ti is the row representing the trust that user i has for each of the other users. User i can specify trust tik for any user k.
If user i does not trust user k
then tik = 0. tik ≠ tki.
uA uB uC uD uE uF
tA 1.0 .7 1.0
tB 1.0 0
tC 1.0 .6
tD .2 .7 1.0 .4
tE .8 1.0
tF .3 1.0
A
B
E
C
D
F
0.7
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Propagation of Trust in the WOT
The trust will then be propagated throughout the WOT to obtain a matrix that contains trust values for all users.
The trust value associated with each path is calculated by applying a concatenation function to multiply the trusts along the path. For example, tik * tkj is the amount that user i trusts user j via k.
A B E D = 0 Aggregate Maximum for tAD is .6A C D = .6
The trust value tik will be recalculated as the trust values change for any of the users.
uA uB uC uD uE uF
tA 1.0 .7 1.0 .6 .072 .24
tB 0 1.0 0 0 0 0
tC .12 .42 1.0 .6 .072 .24
tD .2 .7 .2 1.0 .12 .4
tE .16 .55 .16 .8 1.0 .32
tF .048 .168 .048 .24 .3 1.0
Trust in a semantic association
Trust on a statement function of truth value on the statement and trust on user who placed this truth value
Extending this to a semantic association – function of trusts on individual statements
Trust in a semantic association
Calculating trust in individual statements Calculating trust in the association
User X Calculating trust in a statement S
More than one user can place a truth value on a statement
Trust in S = truth value placed on S by user that user X trusts the most
Calculating trust in a semantic associationOnly as strong as its weakest link. The value of its least trustworthy component.
(statement)
TIPS Architecture
WOT
SWETOBeliefs
Trustaggregator
Queryprocessor(SemDis)
Web Interface
Trust ranking module
Schema
user usertrusts
WOT
trust_value
to_degree
stmt userbelieved_by
truth_value
with_probability
Beliefs
Test Set
Small/manageable set of SWETO instances
Synthetically generated 15 WOT usersAdded corresponding nodes to the graphGenerated synthetic trust relationships
Random values between 0 and 1
Synthetically generated statements of truthRandom values between 0 and 1
Test Cases
1. A user requests both unranked and then ranked results for the same query.
1. Unranked results appear in order found.
2. A user adds an explicit truth value to a statement in an association.
1. All corresponding associations are affected2. Some may be now have different ranks
3. A users changes/states and explicit trust in a believer of a statement.
1. Corresponding associations are affected2. Some now have different ranks
References http://lsdis.cs.uga.edu/library/download/SAA+2004-PISTA.pdf http://ebiquity.umbc.edu/v2.1/_file_directory_/resources/58.pdf http://www.eil.utoronto.ca/km/papers/fox-kp1.pdf http://www.ksl.stanford.edu/people/pp/papers/PinheirodaSilva_DEBULL_2003.pdf http://www.cs.washington.edu/homes/pedrod/papers/iswc03.pdf http://tap.stanford.edu/trust04.pdf http://trust.mindswap.org/ http://lsdis.cs.uga.edu/projects/SemDis/Sweto/sweto.pdf http://lsdis.cs.uga.edu/projects/SemDis/ http://lsdis.cs.uga.edu/lib/download/AS03-WWW.pdf http://lsdis.cs.uga.edu/library/download/iswcRanking2004.pdf http://tap.stanford.edu/trust04.pdf http://www.cs.cornell.edu/home/kleinber/auth.pdf http://www.semagix.com/ http://moloko.itc.it/paoloblog/papers/trust2004.pdf