Title: A Survey of Trust and Reputation Systems for Online Service Provision
1A Survey of Trust and Reputation Systems for
Online Service Provision
- Audun Josang,
- Roslan Ismail, Colin Boyd
Presented by Matt Smith
2Outline
- Introduction
- Background for Trust and Reputation Systems
- Security and Trust
- Collaborative Filtering and Collaborative
Sanctioning - Trust Classes
- Category of Trust Semantics
- Reputation Network Architectures
- Reputation Computation Engines
- Commercial and Live Reputation Systems
- Problems and Proposed Solutions
- Discussion and Conclusion
3Introduction
- What risk exists in this online transaction?
Consumer Risk Has to pay for goods before
receiving them Cannot touch and try products
before buying
Service Provider Risk
Bob
Alice
Amazon
This asymmetric risk can be mitigated through
trust and reputation
4Definition 1 (Reliability Trust)
- Trust is the subjective probability by which an
individual, A, expects that another individual,
B, performs a given action on which its welfare
depends.
Gambetta (1998)
5Definition 2 (Decision Trust)
- Trust is the extent to which one party is willing
to depend on something or somebody in a given
situation with a feeling of relative security,
even though negative consequences are possible.
Inspired by McKnight Chervany (1996)
6Definition 3 (Reputation)
- Reputation is what is generally said or believed
about a persons or things character or standing - I trust you because of your good reputation
- I trust you despite your bad reputation
Concise Oxford Dictionary
7Principles of Reputation
- Reputation is one of the factors that trust is
based on - Reputation is someone elses story about me
- Reputation is based on identity
- Reputation exists in the context of community
- Reputation is a currency
- Reputation is narrative (evolves through time)
- Reputation is based on claims (verified or not),
transactions, ratings, and endorsements - Reputation is multi-level
- Multiple people holding the same opinion
increases the weight of that opinion
Windley et al
8Research Agenda
- Find adequate online substitutions for the
traditional cues to trust and reputation systems
that we are used to in the physical world, and
identify new information elements (specific to a
particular online application) which are suitable
for deriving measures of trust and reputation. - Take advantage of IT and the Internet to create
efficient systems for collecting that
information, and for deriving measures of trust
and reputation, in order to support decision
making and to improve the quality of online
markets.
9Properties of Reputation Systems
- 1. Entities must be long lived, so that with
every interaction there is always an expectation
of future interactions. - 2. Ratings about current interactions are
captured and distributed. - 3. Ratings about past interactions must guide
decisions about current interactions.
Resnick et al. (2000)
10Trust Transitivity Principle
Reliability Trust Semantic Constraints
11Security and Trust
- Hard Security
- Authentication
- Access Control
- Soft Security
- Social Control Mechanisms
- Trust and Reputation Systems
- Identity Trust
- A measure of the correctness of a claimed
Identity over a communication channel - Provision Trust
- The reliability of authenticated parties, or the
quality of goods and services they provide
Rasmussen Jansson (1996)
12Collaborative Filtering Sanctioning
- Collaborative Filtering
- Collect ratings
- Assumed subject to taste
- Optimistic world view
- Assumes all are trustworthy
- Rating things accurately improves your own
recommendations
- Collaborative Sanctioning
- Collect ratings
- Assumed insensitive to taste
- Pessimistic world view
- Assumes some will have ulterior motives
- Sometimes rating things inaccurately may benefit
you to achieve some goal
Reputation Systems
Recommendation Systems
13Trust Classes
Grandison Sloman (2000)
14Categories of Trust Semantics
- Interpretability of reputation ratings and scores
ex. Washing machine energy consumption ex.
Company fitness
15Reputation Network Architectures
- Centralized
- Server / Clients
ex. Peer-toPeer (P2P) Networks
ex. eBay, Epinions, Digg, etc.
16Outline
- Introduction
- Background for Trust and Reputation Systems
- Security and Trust
- Collaborative Filtering and Collaborative
Sanctioning - Trust Classes
- Category of Trust Semantics
- Reputation Network Architectures
- Reputation Computation Engines
- Commercial and Live Reputation Systems
- Problems and Proposed Solutions
- Discussion and Conclusion
17Reputation Computation Engines
- Simple Summation or Average of Ratings
- ex. Summation eBay, Average Epinions, Amazon.
- Bayesian Systems
- Discrete Trust Models
- Belief Models
- Fuzzy Models
- Flow Models
- Transitive iteration through looped or
arbitrarily long chains - ex. Google PageRank
18Commercial and Live Systems
- eBay
- Expert Sites
- Product Review Sites
- Discussion Forums
- Google PageRank
- Supplier Reputation Systems
- Scientrometrics
19eBay
- Buyers and Sellers can provide feedback
- Positive 1, Negative -1, or Neutral 0
- Can also leave comments
- 1 Smooth transaction, Thank you! (typical)
- -1 Buyers beware! (atypical)
- Resnick et al Findings (2002)
- Buyers provide ratings 51.7 of the time1
- Sellers provide ratings 60.6 of the time1
- 99 positive, neutral1
- Primitive reputation score
- Can be misleading 100 , 10 same 90 , 0
- Comprehensible
- Minor ratings problem Ballot stuffing limited
by transactions - Despite primitive nature and drawbacks the
reputation system seems to have positive impact
on eBay as a marketplace.
20Expert Sites
- AllExperts site of self-proclaimed experts
- Rating on knowledge, clarity, timeliness, and
politeness - Score is numerical average of ratings
- AskMe closed to paying companies
- Advogato open-source programmer community
- Centralized, Flow model
- Others that you are familiar with?
21Product Review Sites
- Epinions
- Reviews consist of
- 1 to 5 star ratings for a set of product aspects
- Written prose
- Users rate reviews
- Not Helpful, Somewhat Helpful, Helpful, or Very
Helpful - Simple Web of Trust
- Users can Block or Trust others
- BizRate
- Vulnerable to ballot stuffing
- Amazon
- Any registered user can comment on any product
- Was this review helpful to you? Yes or No
- Reports of many attacks ballot stuffing
22Discussion Forums
- Slashdot news for nerds
- Kuro5in Technology and Culture
- Others (not in paper)
- Digg digg or bury stories
- SiteSays comment on any site as you browse
users can rate any comment (except their own).
23Google PageRank
- Ranks the best search results based on a pages
reputation. - Links from a web page can be seen as a positive
rating - Security by obscurity
- Trust transitivity to the extreme
24Outline
- Introduction
- Background for Trust and Reputation Systems
- Security and Trust
- Collaborative Filtering and Collaborative
Sanctioning - Trust Classes
- Category of Trust Semantics
- Reputation Network Architectures
- Reputation Computation Engines
- Commercial and Live Reputation Systems
- Problems and Proposed Solutions
- Discussion and Conclusion
25Problems
- Low Incentive for Providing Ratings
- Bias Toward Positive Rating
- Unfair Ratings
- Change of Identities
- Quality Variations Over Time
- Discrimination
- Ballot Box Stuffing
26P1 Low Incentive for Providing Ratings
- Ratings are provided after a transaction has
taken place - Users withhold negative ratings because they are
nice or fear retaliation - Often a user does not benefit directly by
providing a rating - Nonetheless, many do provide ratings
- On eBay 60.7 of buyers and 51.7 of sellers do
Resnick et al. - Why? Perhaps, due to hopes of reciprocal ratings
- Why do people Digg stories?
- Miller et al. (2003) proposed a scheme for
eliciting honest feedback based on financial
rewards. - Other incentives?
- Financial incentive (Cash Epinions, Discounts
BizRate) - Status or rank
- Community reciprocity?
27P2 Bias Toward Positive Rating
- There is often a positive bias when ratings are
provided - On eBay only 0.6 of ratings by buyers and 1.6
of ratings by sellers were negative Resnick et
al. - Other examples?
- Possible explanation
- Positive given in hope of receiving a positive
- Negative not given because of fear of retaliation
- Possible solution
- Anonymous reviews and/or ratings (e.g., Digg,
SiteSays) - Cryptographic scheme for anonymous ratings
proposed by Ismail et al. (2003)
28P3 Unfair Ratings
- Finding ways to avoid or reduce the influence of
unfairly positive or unfairly negative ratings is
a fundamental problem in reputation systems - Categories of proposed solutions
- Endogenous Discounting of Unfair Ratings
- Exogenous Discounting of Unfair Ratings
29Unfair Ratings Endogenous Discounting
- Description of Category
- Exclude or give low weight to presumed unfair
ratings based on analyzing or comparing the
rating values to themselves - Assumption
- Unfair ratings can be recognized by statistical
properties - Proposed Solutions
- Statistical Analysis Dellarocas (2000) and
Withby et al. - Collaborative Filtering Chen Singh (2001)
- Other Endogenous Discounting Methods
- ?
30Unfair Ratings Exogenous Discounting
- Description of Category
- Methods where the externally determined
reputation of the rater is used to determine the
weight given to ratings - Assumption
- Raters with low reputation are likely to give
unfair ratings and vice versa - Proposed Solutions
- Bayesian Reputation Engines Buchegger Le
Boudec (2003) - P2P Network of Gnutella Cornelli et al. (2002)
- Trust Builder for rating subcontractors Ekstrom
Bjornson (2002) - Weighted Majority Algorithm variant Yu Singh
(2003) - Other Exogenous Discounting Methods
- Google PageRank
- ?
31P4 Change of Identities
- Reputation systems generally assume
- Identities and pseudonyms are long-lived,
allowing ratings about a particular party from
the past to be related to the same party in the
future. - Changing identities is generally not in the best
interest of the community Gambetta (1990) - Proposed Solutions
- Penalize newcomers Zacharia et. al (1999)
32P5 Quality Variations Over Time
- Description
- Economic Theory indicates that there is a balance
between the cost of establishing a good
reputation and the financial benefit of having a
good reputation, leading to an equilibrium 37,
62. - Variations in the quality of service lead to
variations in reputation - Proposed Solutions
- Discounting of the past Huberman Wu (2003)
- Forgetting factor 32, aging factor 8, fading
factor 7, longevity factor 31 - Discounting can be a function of time or of the
frequency of transactions, or a combination of
both 7
The numbered citations are consistent with the
paper being presented. Please see the paper for
full references
33P6 Discrimination
- Description
- Discriminatory behavior can occur both when
providing services and when providing ratings - Examples and Possible Solutions
- A seller providing good quality to all buyers,
except one (exogenous discounting methods are
designed to solve this situation) - A single rater giving fair ratings except when
dealing with a specific partner (endogenous
discounting methods are designed to solve this
situation)
34P7 Ballot Box Stuffing
- Description
- More than the legitimate number of ratings are
provided. - Solutions / Deterrents
- ratings can only be provided after a transaction
(which costs money) eBay - Only registered users can rate
- Other ideas?
35Outline
- Introduction
- Background for Trust and Reputation Systems
- Security and Trust
- Collaborative Filtering and Collaborative
Sanctioning - Trust Classes
- Category of Trust Semantics
- Reputation Network Architectures
- Reputation Computation Engines
- Commercial and Live Reputation Systems
- Problems and Proposed Solutions
- Discussion and Conclusion
36Basic Criteria for Judging the Quality and
Soundness of Reputation Computation Engines
- Accuracy for long-term performance
- Weighting toward current behavior
- Robustness against attacks
- Smoothness
Dingledine et al. (2000)
Josang et al. claim that criteria (1), (2), and
(4) are easily satisfied by most reputation
engines except for the most primitive (e.g., eBay)
37Challenges Reiterated
- Unfair ratings
- Ballot stuffing
- Cheap pseudonyms
- Obtaining Ratings
- Little incentive
38Reliability and Robustness
- Reliability of the current commercial systems is
questionable - Assuming that reputation systems give unreliable
scores, why the are they used? - Possible answers
- Even though it is not robust it might serve its
purpose of providing incentive for good behavior
if participants think it works Resnick et al. - Even though it might not work well in the
statistical normative sense, it may function
successfully if it swiftly reacts against bad
behavior ( stoning) and if it imposes costs for
a participant to get established (initiation
dues) Resnick et al. - Do not need to be robust because their value lies
elsewhere - Serves as a social network to attract more people
- Positive bias may be desirable from a business
perspective
39Robustness
- Whenever robustness is crucial
- Measures should be taken to protect the stability
- Such as,
- Include routine manual control
- Keep the exact details of the computation
algorithm and how the system is implemented
confidential security by obscurity Epinions,
Slashdot, Google - They note, if ratings were objective it would be
much simpler to achieve high robustness
40No single solution
- There is no single solution that will be suitable
in all contexts and applications - Do you agree?
41Conclusion
- Commercial
- Relatively simple schemes
- Academic
- Advanced features, but lack coherence
- Period of Pioneers
- We hope that the near future will bring
consolidation around a set of sound and well
recognized principles for building trust and
reputation systems