Database Modification

1. Database modifications can cause violations of referential integrity. To preserve the referential integrity constraint

   

   in the following operations:

   • Insert: if a tuple is inserted into , the system must ensure that there is a tuple in such that , i.e.

     

   • Delete: if a tuple is deleted from , the system must compute the set of tuples in that reference :

     

     If this set is not empty, either reject delete command, or delete also the tuples that reference .

   • Update: two cases
     • updates to referencing relation: test similar to insert case must be made, ensuring if is new value of tuple,

       

     • updates to referenced relation: test similar to delete if update modifies values for primary key, must compute

       

       to ensure that we are not removing a value referenced by tuples in .