Distributed Collaborative Graphics Editing Systems In The Environment Research

The Object-based Cooperative graphics Editing System (OCES) in distributed environment is now a very active research area of Computer Supported Cooperative Work. To support free and natural interaction, this kind of system should have such characteristics as collaborative distribution, interactive in real-time and operation's non-restriction. In order to satisfy these features, the fully replicated architecture should be used. One of the key problems in studying and designing the replicated collaborative editing system is the consistency of the multi-duplicated data view, and it's also the key problem discussed in this thesis.Technologies supporting consistency preservation based on a consistency model, which includes three consistency properties, are first surveyed. Our focus is how these properties are maintained. Several representative consistency schemes explored by other researchers are also introduced.Then an object-based multiple versions scheme and some techniques supporting this scheme are discussed. The emphasis is to on MOID, a multiple object versions identification model, and a garbage collection strategy, and also MOVM, a multiple object versions management framework. MOID is able to identify all objects and object versions made from the same original object, and also meets the following three properties: uniqueness, traceability and consistency. Compared with other model, MOID distinguishes a special kind of relationship from compatible relationship, the same concurrent relationship, and successfully resolves the inconsistency of identification related with different executing order of the same concurrent operations. The garbage collection strategy can be applied to clear redundant operations in operation log. Based on this strategy, a new algorithm of Delete is devised. The ability to undo is an indispensable feature of OCES, and undo is related closely with the consistency preservation. MOVM supports undo and itself is a framework to manage version creation, version deletion and version recreation involved in operations' do, undo and redo.A prototype system, CoDraftPaint, is built as a test-bed for the proposed strategies. Other related cooperative techniques used in this prototype, as well as its runtime performance, are also discussed briefly in the end of this thesis.