  Distributed Constraint Optimization (DCOP) is a powerful framework for
representing and solving distributed combinatorial problems, where the
variables of the problem are owned by different agents. Many multi-agent
problems include constraints that produce different gains (or costs) for the
participating agents. Asymmetric gains of constrained agents cannot be
naturally represented by the standard DCOP model. The present paper proposes a
general framework for Asymmetric DCOPs (ADCOPs). In ADCOPs different agents may
have different valuations for constraints that they are involved in. The new
framework bridges the gap between multi-agent problems which tend to have
asymmetric structure and the standard symmetric DCOP model. The benefits of the
proposed model over previous attempts to generalize the DCOP model are
discussed and evaluated. Innovative algorithms that apply to the special
properties of the proposed ADCOP model are presented in detail. These include
complete algorithms that have a substantial advantage in terms of runtime and
network load over existing algorithms (for standard DCOPs) which use
alternative representations. Moreover, standard incomplete algorithms (i.e.,
local search algorithms) are inapplicable to the existing DCOP representations
of asymmetric constraints and when they are applied to the new ADCOP framework
they often fail to converge to a local optimum and yield poor results. The
local search algorithms proposed in the present paper converge to high quality
solutions. The experimental evidence that is presented reveals that the
proposed local search algorithms for ADCOPs achieve high quality solutions
while preserving a high level of privacy.
