How is interactivity handled in MPEG-4?

Interactivity in MPEG-4 Systems is separated into two major categories: client side and server side. The former is available locally at an MPEG-4 terminal while the latter requires communication between the terminal and the sender. Client side interactivity can be further divided in simple object manipulation (repositioning, hiding, changing attributes, etc.) that does not require normative support from the standard, and more general types of events (hyper linking, triggers, etc.) that do require normative support. Note that server side interactivity also requires normative support. Client-side interactivity is handled via VRML's ROUTE mechanism, that links event source fields to event sink fields in the BIFS node tree. Server-based interactivity is provided via a Version 2 BIFS node, called ServerCommand. Additional interactivity can be provided by an application, by translating application events into local scene description updates. Sophisticated interactive applications can be created using the programmatic features of MPEG-4 Systems (ECMAScript as well as Java).