On the definition of forward and backward citation generations

A publication exerts direct and indirect influence on other articles (by citing articles and by articles that cite citing articles) and is itself influenced directly as well as indirectly (by references and references of references). This citation network leads to generations of citing and cited publications. In this contribution we show that these generations can be defined in different ways. We also propose methods to calculate indicators derived from these citation generations. We claim that, when studying a publication's contribution to the evolution of its field or to science in general, taking only direct citations into account, tells only part of the story. (C) 2010 Elsevier Ltd. All rights reserved.