An important trait of a heterogeneous database system is its ability to stay synchronized with the component databases in terms of their schema and data changes. For example, a system that allows users to interface directly with component databases is data-synchronized with the component databases. Conversely, a system that allows users to interact with component databases via a data warehouse cannot inherently be synchronized with the component databases. Similarly, systems that are based on global schemas or support local views of heterogeneous databases, need to be able to reflect the structural (schema) changes of component databases whenever they occur.
If a heterogeneous database system cannot be kept synchronized with the component databases, they need to be periodically brought in synch with these databases. The speed, complexity, and frequency of such synchronization processes are important in characterizing a heterogeneous database system.
Heterogeneous database systems should also be characterized by their ability of tolerating the growth of component databases and of incorporating new component databases. The growth of component databases, for example, could interfere with possible limits on the size of a data warehouse or require slow update processes.
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