Querying Object Tables - Quiz Explanation

The answers you selected are indicated below, along with text that explains the correct answers.

1.	What is the correlation argument for the `DEREF` operator? Please select the best answer.
	A.	Like `VALUE` and `REF`, `DEREF` expects a table name alias as its correlation argument.
	B.	The correlation argument is the object name.
	C.	The correlation argument is the object type.
	D.	The correlation argument is the `REF` (reference) to the object.
	Answer D is correct. `DEREF` is a dereferencing operator and returns the object when a reference is passed to it. Hence, answer D is correct. Answer A is incorrect because `DEREF` expects a `REF` as the correlation argument. Answer B is incorrect because the object name is not a valid argument. Answer C is incorrect because the object type is also an invalid argument.

2.	What is the difference between `REF` and `DEREF` operators? Please select the best answer.
	A.	`REF` returns a reference to the object and `DEREF` returns the object itself.
	B.	`REF` returns the object and `DEREF` returns the `REF` of the object after dereferencing it.
	C.	There is no difference.
	D.	`REF` returns the value of the object and `DEREF` returns the object itself.
	Correct answer is A. A REF operator returns the OID of the referencing object and `DEREF` returns the object itself after accepting the `REF` as a correlation argument. Hence, answer A is correct. Answer B is incorrect because `REF` does not return the object. Answer C is incorrect because `REF` and `DEREF` are completely opposite operators. Answer D is incorrect because `REF` does not return the value of an object.

Oracle SQL

3.	To view the data of the object that is referenced within another object, which operator--`REF`, `DEREF`, or `VALUE`--should you use in a query? Please select the best answer.
	A.	Use the `REF` operator because it returns the reference to the object within an object table.
	B.	Use the `DEREF` operator because the reference must be dereferenced before displaying the data of the referenced object.
	C.	Use the `VALUE` operator because it returns the complete object.
	D.	Use a combination of the `REF` and `DEREF` operators to return the data from the referenced object.
	Answer B is correct . Answer B is correct because the `DEREF` operator dereferences the reference to the object table and returns data from the associated object. Answer A is incorrect because the `REF` operator returns the reference to the object, which is a 128-character OID. Answer C is incorrect because the `VALUE` operator returns the complete object, that is, all the columns and attributes (if applicable) of the object table, but no data from the associated reference. Answer D is incorrect because a combination of the `REF` and `DEREF` operators is not required to accomplish this task.