1. A system for managing online documents, the system comprising: a sheet data store configured to store a plurality of sheets, wherein each sheet includes a set of rows, and wherein each row includes a set of columns; an interaction monitoring engine configured to monitor interactions by users with the plurality of sheets; an interaction data store configured to store records of the interactions monitored by the interaction monitoring engine; a sheet metadata data store configured to store sheet metadata representing relationships between sheets of the plurality of sheets; a collaboration graph generation engine configured to generate a collaboration graph that represents relationships between the sheets and the users based on the interaction records and the sheet metadata; and a collaboration graph analysis engine configured to analyze vertices the collaboration graph for similarities.