Trust on the
Seyyed asgary ghasempouri
Sharif University of Technology
Web of Trust?
Objective of paper & Contributions
Networks in Semantic Web?
How to build a Trust Network?
Computation of Trust
Trust Web Service
Applications -> TrustBot, TrustMail
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Web of Trust?
Web of trust-> each user explicitly specify a
(possibly small) set of users she trusts. The resulting
web of trust may be used recursively to compute a
user‟s trust in any other user
Web of trust
Research has been concentrated more on source of
information which misses trust in terms of human sense.
Focused largely on digital signatures, certificates,
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Apply social networks to semantic web
Consider trust in to account with a much more
Ex: How much credence should I give to a what this
person says about a topic
The degree of trust associated with it could be based on
your past encounter or could be based on what your
friends says about him
Build a Trust Network extending FOAF ontology &
by adding their own Trust Ontology
Compute trust values between two people
Illustrate its usefulness using applications
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Networks on Semantic Web
Information is machine readable
Concepts in semantically marked up pages are
automatically linked through ontological relations
visualized as a large graph where web resources are
nodes & edges form relations between objects or
Generating Social Networks
Individuals manage data about themselves and
Information about individuals in a network is
maintained in distributed sources
Digital signature can be associated to files going
across the network
Security measures builds trust about the
authenticity or data contained within the network
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Building Trust Network
FOAF can be used to describe information
about himself, such as name, email address,
homepage, people he knows
Extended FOAF ontology (Friend-Of-A-Friend)
Following properties were added to it, which allows users to
indicate a level of trust for people they know
Trusts neutrally, Trusts slightly, Trusts moderately, Trusts
highly, Trusts absolutely
Distrust absolutely, Distrust highly, Distrust moderately,
Users can sign these files so that information
source can be verified Sharif University of Technology 6
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Directed Edges in the graph contain explicitly
specified trust values
It can be used to infer the trust values between two
people who are not directly connected
Several Basic calculations
Maximum and minimum capacity paths
Identify the trust capacity of the paths with highest
Determined by making a network flow calculation for
each individual path between the source and sink
Maximum amount of trust a source can give to a
sink is limited by the smallest edge weight along the
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Trust Graph Contd..
Maximum and minimum length paths
measure of the number of edges between the source
and the sink
Weighted average between two people (node X & Y)
General notion is that users would want lower trust
ratings for someone many links away as opposed to
a direct neighbor
Distrust notion is very ambiguous:
Ex: A distrust B regarding a specific subject and in turn, B
distrust C on that subject, it is possible that A distrust C, or
A trust C.
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It uses the maximum
capacity of each path to the
Algorithm is recursive &
calculates the average
For any node that has direct
edge to sink node , they
ignore the paths & use the
direct edge weight.
Otherwise they determine
the weighted average
values for each of the
neighbors, which have a
path to sink
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Trust Web Service
Trust Web service
A web users can provide two email addresses &
in return the service would return the weighted
User can provide their own algorithms for
It retrieves the neighbors, gets the list of trust
rating for a given edge, detecting the presence or
absence of path between two individuals, &
finding path lengths.
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TrustBot is an IRC bot.
Gives trust recommendations when call is made
Builds an internal representation of the trust
network from a collection of distributed sources.
User can query from IRC channel, & the bot
returns the trust values
Provides the weighted average, as well as
maximum and minimum path lengths, and
maximum and minimum capacity paths
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Applications - TrustMail
Email client, developed on top of Mozilla
provides an inline trust rating for each email
calls the web service, passing in the email
address of the sender & mailbox address
If a user has a trust rating with respect to email,
that value is used else general trust rating is used
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Two groups of people
Each group has a Professor & set of students
The two professors know each other & have their trust
ratings in trust Graph
“My advisor has collaborated with you on this topic in the past
and she suggested I contact you.”
Professor on receiving the email needs to verify either by
calling the other professor etc..
Using TrustMail reduces this by providing trust ratings for each
emails & may be with respect to the email subject topic
TrustMail lowers the cost of sharing trust judgments across
widely dispersed and rarely interacting groups of people
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Social Network & application of “small world”
”Small World” notion by Stanley Milgram, almost everybody
in the world are at most separated by “six degrees of
Complex networks show this “small world” phenomenon
Small average distance between two nodes, a high
connectance or clustering co-efficient
“Smallworld” have been studied with respect to random
graphs. Studies have been undertaken with respect to
spread of diseases between networks
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Related Works -Trust on the
Yolanda Gil and Varun Ratnakar
Addressed trusting content and information sources
Users included the credibility and reliability values while
Their trust assessments were based on individual feedback
about the source of information
Trust values are averaged and presented to the viewer.
Uses TRELLIS system, users could view information,
annotations (averages of credibility, reliability etc) and then
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Social Networks exists in the current web
In current web, its hard to determine the topic
based on which the clustering (or social
networks have been formed)
In Semantic Web everything is machine
readable, & trust information can be
annotated along with FOAF, so that trust can
be associated with individuals in social
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Trust network is a directed graph with nodes
forming the person and edges forming the
Trust value computed is based on the
Priority is given to direct link between two people
Otherwise they try to find a weighted average of
the path between X & Y.
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Concept of trust and distrust is subjective,
there can be several different metrics for
inferring trust values between two people
Authors, do not concentrate of developing an
optimal algorithm for computing trust
Authors focus on simple algorithm
They try show some applications in which
trust ratings can be used- TrustMail
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Good thing about the paper is that they build
trust networks on semantic web in a much
more human sense.
They show that some of the applications like
TrustMail can utilize the trust ratings.
Their claim is that Trust values can be
inferred between two people even though
there isn‟t direct trust rating.
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Jennifer Golbeck link to Web of Trust,
Trust Networks on the Semantic Web -
Jennifer Golbeck, Bijan Parsia, James
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