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The figure shows the containment hierarchy for instance types--in other words, what types can contain what types. The hierarchy has three levels.

The top level of the hierarchy consists of two types: OraField and OraParameter.

Either of these two types can contain any of the following types, which comprise the second level: OraObject, OraRef, OraCollection, OraBLOB, OraCLOB, OraBFILE, or any scalar type.

An OraObject or an OraRef can contain one or more OraAttributes.

An OraCollection can contain values for multiple collection elements.