Abstract: A method and system for processing and managing requests for concurrent use of data. Nested databases are utilized in order to create different environments in which the data can be accessed and modified. For each transaction which is in existence, there is an indication or reference to a database or subdatabase associated with that transaction. There are also data structures which indicate, for each data item at issue, which database or subdatabase is associated with that item. The use of data structures relating the transactions, subdatabases, and data items allows the creation of spheres of control for the various transactions and subdatabases. Thus, data can be readily shared among a plurality of users. The creation of the subdatabases does not require plural copies of data and the database management system may be implemented using one copy of the data, although multiple copies may be utilized, if desired.