Conceptually, each X3D application is a 3D time-based space that contains graphic and aural objects that can be loaded over a network and dynamically modified through a variety of mechanisms. The semantics of X3D describe an abstract functional behaviour of time-based, interactive 3D, multimedia information. X3D does not define physical devices or any other implementation-dependent concepts (e.g., screen resolution and input devices). X3D is intended for a wide variety of devices and applications, and provides wide latitude in interpretation and implementation of the functionality. For example, X3D does not assume the existence of a mouse or 2D display device.

Each X3D application:

1. implicitly establishes a world coordinate space for all objects defined, as well as all objects included by the application;
2. explicitly defines and composes a set of 2D, 3D and multimedia objects;
3. can specify hyperlinks to other files and applications;
4. can define object behaviours;
5. can connect to external modules or applications via programming and scripting languages.

The X3D system architecture is shown below. This figure was lifted from ISO/IEC 19775-1:2014 and needs to be upgraded to reflect the changes for X3D V4. In particular the event handling is different between the DOM and Classic execution environments in that the DOM environment

1. Does not support
   1. ECMAScript
   2. Prototypes
   3. External Prototype
   4. ClassicVRML or Binary Encoding
   5. X3D V3 event cascades with a single timestamp
2. Does support
   1. Full DOM interaction
   2. Continuously running time
   3. HTML embedded and rendered in X3D scene

Figure 4.1 — X3D architecture

The abstract structure of the sequence of statements that form an X3D world is specified in TBD.