![](bg8.png)
Our model is close to PathTrust (Kerschbaum et al.,
2006), a reputation system for member selection in
the formation phase of a VO. When inviting members
to join a VO, the initiator selects only those mem-
bers whose reputation is above a certain threshold and
probabilistically selects a member to be in the VO,
as we did for reputation-based scheduling in section
6. The reputation is built by aggregating positive and
negative feedback the user submits after transaction
execution. We consider our model more suitable for
Grid systems, since it does not require direct feedback
from users, the utility functions measures directly the
users’ satisfaction.
The GridEigenTrust model (von Laszewski et al.,
2005) integrates trust management as part of the QoS
management system. They consider both direct and
indirect trust, acquired at the level of grid entities and
contexts (i.e. service delivery), after transaction ex-
ecution. It is grounded on the EigenTrust approach
(Kamvar et al., 2003), which uses the notion of tran-
sitive trust: a peer i has a high opinion of those peers
who have provided it good services and therefore,
peer i is likely to trust the opinions of those peers. The
idea of transitive trust leads to a system where global
trust values correspond to the left principal Eigenvec-
tor of a matrix of normalized local trust values.
8 CONCLUSIONS
In this paper, we defined a utility-based reputation
model geared for Grids. The system is general in the
sense that it can be used to rate both users and re-
sources in a VO with respect to issues of interest such
as QoS and resource usage. It also allows an entity
reputation to be aggregated to the level of the Grid in
general.
The model constitutes the basis for a design of a
reputation management system that is being currently
implemented in EU FP6 project GridTrust. Finally,
we carried out simulations of the model to demon-
strate its behaviour regarding completion time and
welfare, both of which showed improvements over
non-reputation-based VOs. We plan to carry out fur-
ther simulations in order to understand better other
behaviour of the model.
ACKNOWLEDGEMENTS
This work is funded by the European Commission un-
der the FP6 IST project GridTrust (project reference
number 033817).
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