Much research has been conducted on information sharing among multiple database systems. According to [1 ], there are six categories of information-sharing systems. Two of these categories which are concerned with homogeneous databases, i.e. database systems that are of the same kind, are not of interest to this research. Among the remaining four categories of heterogeneous databases, three of them contain some element of global schema, i.e. one which integrates a number of schemas belonging to some component database systems. There could be one single global schema, a number of partial global schemas, or a number of dependency schema, which may be described with customized multidatabase language ([7]). The only one categoiy that requires no global integration is called interoperable systems, which is the subject matter of this research. These systems, as defined in [1] have limited global functions which consists of mainly simple data exchange using standardized communication protocols. In addition, these systems do not support full database functionality.
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