A system for managing data items at an electronic data repository with respect to a plurality of parties includes an electronic data repository and a computer processor programmed to receive data items from parties remote from the repository and from each other. The program stores the received data items in the repository. It provides each remote party access only to those data items within one or more data item sets corresponding to the remote party. The program prohibits any remote party from modifying any data item in the repository, and from deleting any data item from the repository, while the data item is part of a data item set of another remote party. A first remote party may access data items in a set corresponding to a second remote party, responsively to the second remote party.