THE FORMALIZATION OF GENERATIVE STRUCTURES WITHIN STRAVINSKY'S "THE RITE OF SPRING" Adriano De Matteis, Goffredo Haus L.I.M. - Laboratorio di Informatica Musicale Dipartimento di Scienze dell'Informazione Università degli Studi di Milano Introduction. In this paper we show how we can formally describe generative structures of musical pieces. We consider as a particular case study "The Rite of Spring" by I. Stravinsky. The concept of Music Object (MO) has a fundamental role in our research. An MO may be anything that could have a musical meaning and that we think of as an entity, either simple or complex, either abstract or detailed, an entity with a name and some relationship with other musical objects. Our formalization has been made by means of an "ad hoc" arrangement of Petri Nets (PNs) and a music algebra (Haus and Sametti, 1992). Music objects are associated to places; music transformations are described by algorithms associated to transitions and are coded by expressions which are based on the set of operators and the syntactic rules we have defined. This approach allows us to describe music objects and their transformations at various levels of representation. Our aim is to show that: 1) it is possible to find a set of general PNs that can work on a number of music pieces, 2) a set of MOs and few of these PNs can partially or completely well formalize the musical material within a composition, 3) this formalization is closely related to musical thinking and practice, because it preserves and shows the hidden structures within music scores. A further case study can be considered the model of Ravel's "Bolero" by Haus and Rodriguez (1993) which is based on an approach very similar to this one.