Lecture Notes in Computer Science 5185

72 F. Pingel and S. Steinbrecher
Unlinkability of ratings and actions: Users want their ratings and actions
to be unlinkable. Otherwise behaviour profiles of pseudonyms could be built.
If the pseudonym becomes linked to a real name, as it often does in a reputation
network, the profile becomes related to this real name as well.
Anonymity of users: Users want to inform themselves anonymously about
others’ reputation to prevent behaviour profiles of their possible interests.
Authorisability of interactions, ratings and reputation computation:
Interactions should only take place between authorised members. Ratings
should only be given by members if an interaction took place between them.
Confidentiality of interactions, ratings and reputations: Though a reputation
system’s functional requirement is to collect ratings, the aggregated
reputation should only be obtainable by members. Concrete users also might
want only a subset of other members to know their ratings and reputation.
There exist countless models to design possible ratings and the reputation
computation algorithm [8]. As outlined in [6] the following requirements hold:
Accuracy of the reputation computation algorithm: The reputation
computation algorithm has to consider all ratings given. This should also
consider long-term performance. Other aspects include soliciting ratings,
but also educing hidden one (e.g. lack of rating). It should be possible to
distinguish between newcomers and users with bad reputation.
Trustworthiness of the raters: Existing social networks, and weighting recommendations
according to the trustworthiness of the raters should be used
to scale the reputation computation algorithm to the needs of the one who
wants to inform himself about others’ reputation.
Self-correction: If a user agrees not or no longer with certain ratings for a
certain reputation object, he should correct both the trust values for the
corresponding raters in the reputation computation algorithm and the reputation
of the reputation object.
These requirements show the need for individual reputation in contrast to the
common concept of global reputation. Due to the need of multilateral secucurity
we also favoured global repuation and had to neglect the last two requirements
above to reach anonymity and unlinkability of the uders involved.
2.2 Cross-Community Reputation Management
With the help of cross-community reputation a significant reputation can be
built up easily in short time even in very small communities.
The reputation system should be independent from the communities the reputation
it aggregates s used for. The reputation system provides the communication
protocols necessary. But it might offer the communities the possibility to
define their own reputation computation algorithm that should be used by the
reputation system. In practice this will mean that the reputation visible in the
communities will differ. For this reason the ratings given should consist of