I have question on the constraint state "Disable Validate". Actually, I don't know the meaning behind. I have read the Oracle manual which reads:

"DISABLE VALIDATE disables the constraint, drops the index on the constraint, and disallows any modification of the constrained columns."

What I understand about DISABLE and VALIDATE is that DISABLE disables the constraint. VALIDATE ensures that existing data conforms to the constraint.

Why DISABLE VALIDATE will disallow any modification of the constrained columns?
Also, what is the use of setting contraints in this state?

Could someone please offer explanation?

Please help. I get stuck in it.