for the first question ...........there is nothing like a field addition in IMS DB.....what ever we add are segments through program in IMS DB.......i am not sure if the interviewer know IMS or you have wrongly took the question........
for secong question .............referential intergrity terms are related to relational database management systems like DB2.........there will not be any such instance in IMS as IMS is a hierarchial database management system........probably the question is wrongly taken by you or the interviewer himself is in confused state when he asked this question.....
Nilu is correct.
Here is the of information regarding your questions:
There is no field adding in ims db.
Segment is the smallest unit of information that a DLI transfers between IMS Buffer Pool and application program....filelds are defined in Segment....and there is no question of adding fields in ims database
(Segment type is simply a catagory of data which contains characteristics of segment...this is formed with collection of fields)
Since referencial integrity is established between two or more tables in Relational database(this relation is made physically)
where as in IMS DB there will not be any physical relation ship between two databases...only logical relation ship exists that is through PSB(Program Specification Block)