Negotiating data access in federated database systems

A protocol is presented for negotiating access to data in a federated database. This protocol deals with several important aspects of data sharing in an environment where databases belonging to different organizations coexist and cooperate. It is based on the concept of quasicopies. These are cached values that are allowed to deviate from the central value in a controlled fashion. The degree of consistency of a quasicopy is established by the entity where the quasicopy is to reside. Two techniques are presented that can be used for numerical data and for copies that rely on version numbers. It is believed that these two ideas encompass many of the interesting cases in practice. However, it is also possible to fine tune the estimation of this function once the exact semantics of the data involved are known.<>