ObjectStore is the primary product of ObjectDesignInc.  It's an OODBMS that at least in Java, is fairly intrusive into your system.  It seems to have very good performance, though...
-- KyleBrown

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Well, I'm not sure what he means by "intrusive".  In some ways yes, in other ways no.

See "The ObjectStore Database System", Communications of the ACM, 34(10), 1991.

-- DanWeinreb

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ObjectStore is also a generic term for an object-oriented data store. It is often used in comparison to a DataStore, a generic term for a data source. A canonical ObjectStore offers input and output streams of Object instances.
-- TomStambaugh

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[CategorySoftwareTool, CategoryDatabase, ObjectOrientedDatabase]