A study of concurrency control in Web-based distributed real-time database system using extended time Petri nets

The Web-based database system has both distributed and real-time features. In addition to satisfying data consistency requirements as in conventional distributed database systems, concurrency control in Web-based distributed real-time database systems (DRTDBS) must also satisfy timing constraints, such as deadlines associated with transactions. So, the concurrency control problems become more complex and extremely difficult in a Web-based DRTDBS. Petri nets are promising tools for modeling and analysis information processing systems that are characterized as being concurrent, asynchronous, parallel and distributed. An extended time Petri net model for describing and analyzing the concurrent control of the Web-based DRTDBS is presented in this paper. The model has features of deadlock-free and serializability and can prevent useless restarts and useless waits. We compose the reduced Petri net models of all sites into a Petri net model for globe concurrent transactions using synchronizing composition. Moreover, the paper largely reduces the scale of the Petri net model for every site with reduction technique before composing. It solves the state explosion problem in reachability analysis of Petri nets. Last, a sufficient and necessary condition for judging whether the whole system is deadlock is given in the paper.