How to get the validation for the dependent flex fileds?

Hai Experts,

             How to get the validation for the dependent flex fileds? For example you have 2 values set 'My Value Set1' and 'My Value Set2'. And 2nd one is dependent on First. From PL/SQL how we can validate a perticuklar vlaue is valid as per Value set 'My value set2'?
For Example :
My Value Set1 Values: 1,2,3,4
My Value Set2 Values: 
For 1 (My Value Set1 Value) - 100,200
For 2 (My Value Set1 Value) - 1000,2000
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From Pl/Sql How can we validate 100 as the valid value as per 'My Value Set2' 

Thanks In Advance

Saravanan V