Can peer-to-peer (P2P) reputation systems work?
Some of the successful and well known reputation systems on the
web are controlled and managed by a central entity. An example that
I have used in the past is the eBay feedback system. eBay enables
buyers and sellers to rate other buyers and sellers, and presents
that reputation information to everyone. Another example is the
industry for digital certificates in which there are a few large,
trusted "authorities" who vouch for the reputation of the
certificate holder. In both of these examples, the reputation system
is controlled by a large corporation - giving that company a lot of
power, competitive leverage, etc.
Since power in the hands of large corporation can easily corrupt,
the idea of a peer-to-peer reputation system - one that is
not controlled by a single entity - is very appealing to many
(including myself). But can such a system work? And if so, how?
First, I think we need to look at the main reasons why
centralized reputation systems are successful. One of the most
important reasons is trust. These systems work because people
trust the reputation information presented by them. When look at the
eBay reputation of someone, I have a high degree of confidence that
the person's feedback score is accurate - I don't stop to wonder if
that person has hacked the eBay system and changed the score. The
eBay system works a s a reputation system because people trust
eBay.
But in a P2P approach, there is no large, recognizeable
organization. Reputation information would be hosted in many
different places, perhaps on the web sites or computers of
individuals whom you do not know. So how do you know that you can
trust these people? In order to trust them, you need to learn about
their reputation.....here the problem becomes circular in nature.
Can can we be confident that reputation information information in a
P2P system is not forged or manipulated? One solution that comes to
mind quiclky is that the reputation information could be stored in
more than one place - in which case an anomoly could indicate
attempts to forge data. But what happens when reputations
legitmately change - the change must propagate to other nodes - how
do you know that it is a real change and not a forged change? How
can we trust reputation information in a peer to peer
system?
For the answer, I think we need to look at the most common
reputation system of them all, one that has been around for
thousands of years: word of mouth. For moment, let us forget about
the web, TV, radio, newspapers - without these sources of
information, how do we learn about the reputation of others?
Personal interaction is the first way we can do this. If we buy
products from a vendor at a (social) market, based on the quality of
the products and the vendor's claims, we develop and opinion about
the reputation of that person. Another way is by talking to others,
sharing our opinions about the reputations of others. If I believe
that the market vendor has a good reputation, and John believes the
same, it reinforces my opinion of the vendor's reputation. But what
if Mary tells a story about the vendor in which she was cheated?
That might decrease my opinion of the vendor. This also works for
people we have never met. Before I walk into a new shop, I might ask
a few people about their opinions and experiences with the shop
owner. Some of the people I ask may not have been in the shop
either, but may relate stories that others have told them. This way
I gather reputation information for someone that I never met -
which is exactly what we need to do on the web! but what
happens if I get 10 conflicting opinions about the shop owner? How
do I use these to form my own opinion? The answer again is
trust. Some opinions I will weight heavier than others,
depending on how much I trust the person giving the opinion -
depending on their reputation. I trust the opinion of my best
friend more than that of a casual aquaintance. This raises an
important difference between a centralized reputation system and a
word-of-mouth system: with a word-of-mouth reputation system,
reputation is relative, not absolute. In the real world, a
person's reputation is seen throught the eye of the beholder. Can
we harness this word of mouth system on the Internet?
The word-of-mouth system, as described above relies on a
social network to gather and disseminate reputation
information. Online social networks can be used in the same way,
whether they are centralized systems or peer-to-peer. Now we can
revisit the question: how can we trust reputation information in a
peer to peer system? The answer is that you trust the people that
you know best, just like in the word-of-mouth system. Online social
networks already track the friend-of-a-friend and six degrees of
seperation, and P2P applications can do the same. Members just need
to input the reputation information for the people that they know
directly, and reputation information could aggregated and
persoanlized based on each person's trust level and degrees of
separation. This way you don't need a big corporation to "trust",
you just need to trust your friends. Perhaps some of the online
social networks are already moving in this direction, I am not sure.
But it seems to me that the answer is "Yes", P2P reputations systems
can work.
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