Distributed Collaborative Version Control Technology

The Object-based Cooperative Graphics Editing System (OCGES) in distributed environment is now a very active research area of Computer Supported Cooperative Work (CSC W). To support free and natural interaction, this kind of system should have the following characteristics: (1) distributed; (2) real-time; (4) transparent; (3) unconstrained. The requirements for good responsiveness and for supporting unconstrained collaboration have led us to adopt a replicated architecture for the storage of shared documents. One of the most significant challenges in designing and implementing real-time cooperative editing systems with a replicated architecture is consistency maintenance of replicated documents, which is also the key problem discussed in this paper.Technologies supporting consistency maintenance based on a consistency model, which includes three consistency properties, are first surveyed. Our focus is how these properties are maintained. Several representative consistency maintenance schemes explored by other researchers are also introduced.Then a distributed collaborative multi-versioning scheme based on version replication and some supporting techniques are discussed in detail. Major technical contributions of this work include a version expression scheme, a formal specification of a unique combined effect for an arbitrary group of conflict and compatible operations, a distributed algorithm for incremental creation of multiple versions (MVIC), a consistent version identification scheme for multiple versions (CVID), a target version recognition scheme (TarVER), and a multi-versioning management scheme.The version expression scheme can preserve information of mid-versions, which is helpful for users to trace their views back. The MVIC algorithm can efficiently resolve those discordant conflicts induced by geometrical/non-geometrical attributes, and can also support non-reversibility of geometrical resolution of complex graphic objects. It's a general strategy for cooperative graphics editing systems. The CVID scheme is able to identify all versions and also meets the following three properties: uniqueness, traceability and consistency. Compared with other models, the CVID distinguishes a special kind of relationship from compatible relationship, the same concurrent relationship, and successfully resolves the inconsistency of identification related with the same concurrent operations.All algorithms and schemes presented in this paper have been implemented and verified in an Internet-based prototype system CoDraftPaint.