Watching Systems In Graphs: An Extension Of Identifying Codes

We introduce the notion of watching systems in graphs, which is a generalization of that of identifying codes. We give some basic properties of watching systems, an upper bound on the minimum size of a watching system, and results on the graphs which achieve this bound; we also study the cases of the paths and cycles, and give complexity results. (c) 2011 Elsevier B.V. All rights reserved.