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Co-authored documents are becoming increasingly important for knowledge representation and sharing. Tools for supporting document co-authoring are expected to satisfy two requirements: 1) querying changes over editing histories; 2) maintaining data consistency among users. Current tools support either limited queries or are not suitable for loosely controlled collaborative editing scenarios. We address both problems by proposing a new persistent data structure-partial persistent sequence. The new data structure enables us to create unique character identifiers that can be used for associating meta-information and tracking their changes, and also design simple view synchronization algorithms to guarantee data consistency under the presence of concurrent updates. Experiments based on real-world collaborative editing traces show that our data structure uses disk space economically and provides efficient performance for document update and retrieval.