14. Specifying Intermedia Synchronization with a Domain-Specific Language: The Nested Context Language (NCL)

This chapter reports on the intermedia synchronization features of Nested Context Language (NCL), an XML-based domain-specific language (DSL) to support declarative specification of hypermedia applications. NCL takes media synchronization as a core aspect for the specification of hypermedia applications. Interestingly, NCL deals with media synchronization in a broad sense, by allowing for a uniform declaration of spatiotemporal relationships where user interactivity is included as a particular case. Following the W3C trends in modular XML specifications, NCL has been specified in a modular way, aiming at combining its modules into language profiles. Among the main NCL profiles are those targeting the domain of Digital TV (DTV) applications. Indeed, NCL and its standardized player named Ginga are part of ITU-T Recommendations for IPTV, Integrated Broadcast–Broadband (IBB) and DTV services, and Integrated Services Digital Broadcasting—Terrestrial (ISDB-T) International standards. This chapter discusses the main reasons that make NCL a comprehensive solution for the authoring of interactive multimedia applications. It also discusses the aspects of its conceptual model, the Nested Context Model (NCM), which defines an intrinsic support for easily specifying spatiotemporal synchronization among components (e.g., media and input assets).