Abstract In this paper we show how we can formally describe Generative Structures (GS) of musical pieces. We considered as a particular case study “The Rite of Spring”, by I. Stravinsky. The first goal of our research has been the identification of relationships among Music Objects (MOs) belonging to the piano duet or the orchestral score or both. Our formalization has been made by means of an “ad hoc” arrangement of hierarchical Petri Nets (PNs) and a music algebra; music objects are connected to places; music transformations are described by algorithms connected to transitions and are coded by expressions which are based on the set of operators and the syntactic rules we have defined.