Serializability has been widely accepted as the correctness criterion for databases subject to concurrent access. Serializable execution generally requires transactions to hold locks for long periods and thus is inappropriate for high performance database systems or database systems supporting long running transactions. It is also difficult to implement in a federated database system (built of several autonomous database systems, possibly spread over a network) that supports transactions accessing data in more than one of the component systems. In this talk we will describe how the semantics of transactions can be used to define a new correctness criterion that has the potential for improving performance and is more suitable for implementation in a federated database.