Heterogeneous computer systems means computer systems with different storage architectures, computer systems with different central processing units (CPUs), computer systems with different disk organization methods, computer systems with different access methods, computer systems that use different controller interfaces etc. Sharing data indicates that every one of the said computer systems can access the data independently, not relying on services from the other; a single copy of the data is maintained, as opposed to replicated data that is used, in some cases to overcome the same needs. Every system has direct access to the shared data, through the use of emulators that enable applications on every system to use the desired interfaces to the data, disguised as the ordinary local interfaces. A typical example of the use of this invention is accessing an IBM mainframe's DB2 data base from a UNIX environment. A special case of the above example is accessing an IBM mainframe's DB2 database through an Oracle like interface in the UNIX environment. Another use could be a fast down load program that derives an Oracle fast load compatible file from DB2.