A multidatabase system provides integrated access to heterogeneous, autonomous local databases in a distributed system. An important problem in current multidatabase systems is identification of semantically similar data in different local databases. The Summary Schemas Model (SSM) is proposed as an extension to multidatabase systems to aid in semantic identification. The SSM uses a global data structure to abstract the information available in a multidatabase system. This abstracted form allows users to use their own terms (imprecise queries) when accessing data rather than being forced to use system-specified terms. The system uses the global data structure to match the user's terms to the semantically closest available system terms. A simulation of the SSM is presented to compare imprecise-query processing with corresponding query-processing costs in a standard multidatabase system. The costs and benefits of the SSM are discussed, and future research directions are presented.

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Most large organizations have many different kinds of hardware and software. There are various large and small databases scattered throughout the network with different data models and access languages. Each user has a local data source or two that is strategic to their function. However, they also realize that there is more information out in the network, somewhere, that they need. These organizations need a data access system that can accommodate preexisting, heterogeneous, data sources scattered through the network. Multidatabase systems provide a uniform global database interface to exactly these types of systems. This global interface hides all the underlying distribution and heterogeneity of information in the system, so that users can submit a single query to capture data from any or all available databases. In addition, multidatabase systems allow participating local databases to remain autonomous; i.e., the local DBMS determines how to structure local data, what functions to expose to the multidatabase, what global queries it will process, and when it will join or leave the global system. This property of local autonomy means the multidatabase system provides global information access, but the organization does not have to replace its hardware, software, or user training. Organizations keep all their existing function, while adding significant global access capability. Multidatabase systems have their roots in traditional distributed databases, but were significantly influenced by the rise of networks and the connectivity of heterogeneous systems. Traditional distributed databases are designed top-down-the global function controls local DBMSs (which are typically all the same system-homogeneous). Multidata-Integrated Computer-Aided Engineering, 2(1) 1-2 (1995)