Modeling and Evaluation of Software Systems with Object Stochastic Activity Networks M. Abdollahi Azgomi, A. Kamandi and A. Movaghar Abstract—Stochastic activity networks (SANs) are a stochastic generalization of Petri nets. SAN models have been used to evaluate a wide range of systems and are supported by several modeling tools. We have introduced object stochastic activity networks (OSANs) to overcome some restrictions of these models. OSANs integrate the concepts of object-orientation into SAN models. Elements of OSANs and their submodels are defined as classes. OSANs have several distinguishing properties, which are not found in other object-oriented or high-level extensions of Petri nets. In this paper, we will present the definitions, behavior and methods for the solution of OSAN models. Then, we will present the result of a case study on transformation of the UML use case and activity diagrams into OSAN models. The derived OSAN models have been evaluated using our modeling tool called SANBuilder. The object-orientation of OSANs and the flexibility of having functions for activities, make these models more appropriate than other extensions of Petri nets for modeling and evaluation of software systems. Index Terms—Modeling, Evaluation, Petri Nets, Stochastic Activity Networks, Software Engineering, SANBuilder. 1. Introduction Stochastic activity networks (SANs) [Movaghar84] are a stochastic generalization of Petri nets (PNs) [Peterson81]. These models are more powerful and flexible than most other stochastic extensions of Petri nets including notable models such as stochastic Petri nets (SPNs) [Molloy82] and generalized stochastic Petri nets (GSPNs) [Ajmone86]. SAN models have been used to evaluate the performance, dependability and performability of a wide range of systems. These models have been used as a modeling formalism in several modeling tools, such as UltraSAN [Sanders95] and Möbius [Deavours02]. In order to integrate the concepts of object- orientation (OO) into SANs and to overcome some restrictions of these models, we have recently introduced a new extension for SANs, called object stochastic activity networks (OSANs): OSANs = SANs + Hierarchy + Colour + OO [Abdollahi03c, Abdollahi04d]. Primitives of OSANs and their submodels (called super activity) are defined as classes. Tokens of OSANs are objects of a user-defined colour class. These models adapt some useful ideas and features from the existing high-level and object-oriented extensions of Petri nets. However, OSANs have several distinguishing properties that are not found in the existing OO or high-level extensions of Petri nets. We have implemented OSAN models in SANBuilder modeling tool [Abdollahi04a]. SANBuilder provides features for construction, animation, simulation and analytic solution of OSAN and other SAN-based models. As a case study, we have transformed the unified modeling language (UML) use case and activity diagrams into OSAN models. The derived OSAN models have been evaluated using SANBuilder modeling tool. The results of this case study proved that OSANs can be used as a complement or even an alternative of the UML for modeling and evaluation of software systems. This paper is organized as follows. Sec. 2 mentions the motivations of this work and gives a survey on related work. In Sec. 3, the informal definitions, graphical notations, Meta model and an example of OSAN models are presented. The behavior of OSANs is discussed in Sec. 4. In Sec. 5, methods for the solution of OSAN models are introduced. Sec. 6 gives an overview of a modeling tool for OSANs. The transformation of UML use case and activity diagrams into OSANs and their evaluation is presented in Sec. 7. A summary of advantages of OSANs for application in software systems is mentioned in Sec. 8. Finally, in Sec. 9, some concluding remarks are mentioned. 2. Motivations In this section, some motivations of this work and a survey on related work on integration of object- orientation and Petri nets are presented. Technical Report, Department of Computer Eng., Sharif University of Technology, Tehran, Iran. 2004.