The graphical formalism of Petri Nets (PNs) is established on a strong mathematical foundation that can be applied in systems speci®cation, analysis and veri®cation. However, classical (low-level) models suer from the state explosion problem as resulting PNs become larger. Thus, their ability to represent and analyze realistic large scale systems is reduced. High-level PNs have been introduced in order to extend the modeling power of low-level models. This paper presents an assessment of high-level PNs from an engineering perspective. A set of categories is proposed for classifying several extensions presented in the literature. Models which belong to the same category are compared by discussing the formalism, the descriptive power and the inherent limitations of each. All categories are compared using a set of general criteria including compactness, ease of analysis, degree of supporting re®nement/ abstraction and specifying communication. The modeling power of representative models of each category is discussed by presenting illustrative application examples. Ó 1998 Elsevier Science Inc. All rights reserved.

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