A Hierarchical Petri Net Model for SMIL Documents

Abstract

The increasing number of services and products proposed on the Web is mainly marked by the proliferating use of rich media to transmit information. The static Web as it was known during the glorious years of HTML is disappearing to let place to a more dynamic and interactive Web. Synchronized Multimedia Integration Language (SMIL) (SMIL1.0,1998) was developed by the World Wide Web Consortium (W3C) to address the lack of HTML for multimedia over the Web. It provides an easy way to compose multimedia presentations. With the W3C efforts, SMIL is becoming the most popular language in authoring multimedia presentations and it is supported by the newest versions of browsers. In authoring a SMIL multimedia presentation, the author always wants to guarantee the correctness of the SMIL script, not only syntactically but also semantically. However, the complexity of the SMIL synchronization model is such that it is difficult to guarantee the validity of a scenario using non formal methods. On the other hand, the formal techniques based on mathematical models offer a complete formal semantics and propose formal techniques for consistency checking, but are in general time consuming. In order to respect the interactivity constraint in an authoring environment, a formal model for SMIL documents must offer the best compromise between formal verification capabilities and efficiency in terms of computation time. Although many research studies were dedicated to multimedia documents authoring, only few of them has addressed temporal consistency checking problems. Yet, it is clear that the temporal consistency of a document has a direct impact on the quality of the presentation and consequently on the client satisfaction (consider the case of a presentation that stops playing before its end, a part of its semantic is lost). In order to address the lack in SMIL modelling and verification solutions, we have defined a hierarchical temporal extension of Petri Nets, named H-SMIL-Net (Hierarchical SMIL-Petri Net) (Bouyakoub & Belkhir, 2008), for the incremental authoring of SMIL multimedia documents. The H-SMIL-Net model is mapped on the SMIL hierarchical temporal structure to better fit with the modelling needs of this language. The H-SMIL-Net model is based on the SMIL-Net model defined in (Bouyakoub & Belkhir, 2007). In order to better fit with SMIL authoring requirements, we have implemented the H-SMIL-Net model within an interactive authoring environment for SMIL documents. 15