The following is the cause of this error:
The values of a scalar datatype such as CHAR or REAL have a predefined order, which allows them to be compared.
But an object type, such as a some_type, which can have multiple attributes of various data types, has no predefined axis of comparison.
To be able to compare and order variables of an object type, you must specify a basis for comparing them.
Two special kinds of member methods can be defined for doing this: map methods and order methods.
The action you can take to resolve this issue: Define a MAP or ORDER method for the object type.
For more information, you can see https://docs.oracle.com/cd/B19306_01/appdev.102/b14260/adobjbas.htm#sthref211
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