Int. J. System of Systems Engineering, Vol. 4, No. 1, 2013 55 Copyright © 2013 Inderscience Enterprises Ltd. Distributed consensus under ambiguous information Gabriele Oliva* Complex Systems and Security Laboratory, University Campus Biomedico of Rome, Via Álvaro del Portillo 21, 00128, Roma, Italy E-mail: g.oliva@unicampus.it *Corresponding author Stefano Panzieri Dipartimento di Informatica e Automazione, University ‘Roma TRE’, Via della Vasca Navale, 79, 00146, Roma, Italy E-mail: panzieri@uniroma3.it Roberto Setola Complex Systems and Security Laboratory, University Campus Biomedico of Rome, Via Álvaro del Portillo 21, 00128, Roma, Italy E-mail: r.setola@unicampus.it Abstract: This paper addresses the problem of composing different ambiguous and vague pieces of information without a central authority through a set of distributed agents, each with limited perspective, converging to a shared point of view by exchanging information only with a reduced subset of nodes (i.e., their respective neighbourhood). To this end, the distributed consensus problem is extended in the fuzzy fashion. As a result, the framework allows to compose several heterogeneous and ambiguous/linguistically expressed opinions in a decentralised way, both in terms of value with higher belief and in terms of ambiguity associated to the final agreement value. The proposed framework is applied to a case study related to crisis management for critical infrastructures, where human operators, each able to observe directly the state of a given infrastructure (or of a given area considering the vast and geographically dispersed infrastructures), reach a distributed consensus on the overall criticality of a situation expressed in a linguistic, fuzzy way. Such a consensus is reached in terms of actual severity of the scenario (single integrators) or in terms of both severity and evolution tendency (double integrators). Keywords: critical infrastructures; fuzzy systems; consensus; distributed systems. Reference to this paper should be made as follows: Oliva, G., Panzieri, S. and Setola, R. (2013) ‘Distributed consensus under ambiguous information’, Int. J. System of Systems Engineering, Vol. 4, No. 1, pp.55–78.