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When Matterhorn is running on a different server than Avalon and they don't share the same filesystem (and filesystem paths) for both the Rails web upload directory and dropbox, Avalon uses something called a working file path. The working file path is the full path for the file itself, and is used to refer to a copy of the originally uploaded file where Matterhorn has access and at a path shared by both servers. The working file path is stored on the MasterFile so that it can be cleaned up by a background job after the MasterFile has finished processing.
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