A query and transaction specification in VPL is runnable. In particular, the MSQL query is decomposed into several local queries that are passed to the local database systems with the remote call 2 primitive. All local database systems may be incorporated into the multi database system. In the ex treme case, the MDBS might only pass uninterpreted statements to and from the local system. A global data model that is able to represent all possible data and queries will usually not exist.
Local databases are autonomous in their use of transaction models.
Often , only serializable schedules, sometimes strict or rigorous schedules will be produced. Flight tickets are not returned separately after the whole trip has been booked. The example integrates several real transactions on databases into VPL transactions. Example 3 shows the implementation of a small tool for the specification of time out values. Such a tool can be used to keep execution time within boundaries, especially in combination with function replication.