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.