Redes de petri orientadas a objetos

Abstract

This thesis discusses the integration of object oriented concepts and Petri nets modelling of systems. In particular, distributed and concurrent software systems. We argue that the main cause for the unsuccessful object oriented Petri nets notations is the approach used to combine concepts which emphasizes syntactical aspects instead of the semantic ones. We defend that semantic integration principles must guide the combination of syntactical structures in an orthogonal way. This approach promotes the development of notations that are more easily accepted by designers, since i t minimizes the influence the paradigms have on each other. The essence of each language is better preserved this way. Also, it maximizes the chances of adapting the existing analysis techniques, because most of them depend on semantical aspects. Present notations combine concepts in a syntactical way. Such approach does not provide two complementary, articulated views of the models. Instead, it provides a single statically compound view. One of the main reasons is the unbalanced integration of concepts. Because object orientation is often explained informally, formalizations are clearly Petri-net biased. This has two consequences. First, it forces different interpretation for existing concepts of Petri nets, so they can be adapted to object language. This has a severe impact on the chances of adaptation of existing techniques, because they rely heavily on concepts whose interpretations are modified. Second, it forces the adaptation of object concepts, so they fit well within Petri nets. This leads to a loose/weak characterization of the object paradigm and, as a consequence, to a badly accepted notation. As a result, we present an integration strategy that avoids the problems mentioned above. The strategy consists on balancing the emphasis and the role that each paradigm has on the proposed notation, assuring that the notation and its meaning are defined in a orthogonal way, and defining a semantic composition of the involved concepts. In practice, this was achieved through the explicit adoption of a conceptual computing model for concurrent and distributed systems for which the central notion is the object. We also present a (Petri net independent) formalism that allows the modelling of the evolution of concurrent object systems. Finally, we propose an integrated notation, which is based on meaning composition instead of syntactical integration.