Inside MASSIVE-3: flexible support for data consistency and world structuring

MASSIVE-3 is our third generation of Collaborative Virtual Environment (CVE) system. This paper describes the goals, design and implementation of key aspects of the MASSIVE-3 system, and in particular its support for data consistency, and world structuring and interest management. MASSIVE-3 adopts a distributed database model, in which all changes to items in the database are represented by explicit events that are themselves visible to the system. Networking is logically multicast, but physically client-server (the reasons for this are explained). MASSIVE-3 makes application behaviours explicitly visible within the database in the form of “Behaviour” data items. MASSIVE-3 implements and extends work on consistency by the University of Reading. In particular, it adds an explicit “Update Request” data item, which allows the system to support a number of different consistency mechanisms within a single virtual world. World structuring in MASSIVE-3 extends the notion of “Locales” from the SPLINE system to include distinctions based on functional class, organisational scope and fidelity. It also allows flexible and general replication and rendering policies to be specified and used for interest management.