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This paper describes the design and implementation of a file system-based distributed authoring system for campus-wide workgroups. We focus on documents for which changes by different group members are harder to automatically reconcile into a single version. Prior approaches relied on using group-aware editors. Others built collaborative middleware that allowed the group members to use traditional authoring tools. These approaches relied on an ability to automatically detect conflicting updates. They also operated on specific document types. Instead, our system relies on users to moderate and reconcile updates by other group members. Our file system-based approach also allows group members to modify any document type. We maintain one updateable copy of the shared content on each group member's node. We also hoard read-only copies of each of these updateable copies in any interested group member's node. All these copies are propagated to other group members at a rate that is solely dictated by the wireless user availability. The various copies are reconciled using the moderation operation; each group member manually incorporates updates from all the other group members into their own copy. The various document versions eventually converge into a single version through successive moderation operations. The system assists with this convergence process by using the made-with knowledge of all causal file system reads of contents from other replicas. An analysis using a long-term wireless user availability traces from a university shows the strength of our asynchronous and distributed update propagation mechanism. Our user space file system prototype exhibits acceptable file system performance. A subjective evaluation showed that the moderation operation was intuitive for students.
Date of Publication: June 2012