HTSPN: An Experience in Formal Modeling of Multimedia Applications Coded in MHEG or Java

Abstract

Multimedia authoring involves people not familiar with formal design techniques, but eager to check documents against synchronization, scheduling and resource allocation errors. Visual modeling with Petri Nets answers that need with a graphic syntax and a formal semantics that makes models executable. A Petri Net defines a bipartite graph where summits are divided into places associated with data processing functions and transitions which represent synchronization points. The chapter discusses an experiment with Hierarchical Time Stream Petri Nets, a timed extension of Petri Nets which was designed with distributed multimedia systems in mind. HTSPNs define a unified framework to structure complex and interactive documents. Dynamic synchronization strategies based on temporal intervals composition make it possible to take the asynchronous nature of distributed systems into account. Last but not least, a HTSPN remains an open model, which can be extended with implementation details regarding, e.g., the URLs and the presentation characteristics. The interpreted model or I-HTSPN for short, has been instantiated for MHEG and Java, respectively. The MHEG I-HTSPN editor, document checker and code generator were prototyped in C++ for Solaris. The Java I-HTSPN counterpart has been developed in Java. Their use is exemplified on a guided tour of a university and a distance learning application.