Multidatabase systems are networks of interconnected autonomous database management system sites. The different aspects of the autonomy are design autonomy, execution autonomy and communication autonomy. Each site executes local transactions and also subtransactions of some global distributed transactions. An important research topic is achieving concurrency control of global transactions with as little violation of local autonomy as possible. The methods used in distributed (homogeneous) database systems would necessitate considerable violation of local autonomy.
In a multidatabase system, the component database system may be different in structures and behaviors, such as data model representation, interpretation, transaction management, etc. This kind of heterogeneity causes difficulties in managing replicated data. We are studying how to resolve the problems caused by heterogeneity in designing replica control.