Real-time collaborative Web applications allow a multitude of users to concurrently work on a shared document. Especially in business contexts it is often necessary to be able to precisely define and restrict who is allowed to edit which data field of such a shared document. Existing solutions for enforcing such access control restrictions typically rely on a central service, the policy decision point. However, for use cases with unreliable or limited connectivity, such as mobile devices, a permanent connection to this centralized policy decision point can not be guaranteed. To address this problem, we present a novel approach that includes methods for client-side enforcement of access control constraints for offline users, and merging of offline changes, that enables users to edit such access constrained shared documents offline. We propose a generic conflict detection and resolution approach that attempts to resolve merge conflicts that are inherent to access constrained documents automatically while prioritizing online users and maximizing the number of filled out data fields in a document. In addition, we discuss and evaluate our approach via a prototype implementation.

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