Difference between logical data independences and physical data independences.Whish is harder to achieve and why?
Answers
PHYSICAL DATA INDEPENDENCE:
physical storage structure or devices can be changed without affecting conceptual schema
Modification are performed to improve performance
It is not difficult because, we have to only replace the data from one device to another device. No need to change the data only change the location of data
It provide independence and immunity to conceptual and external schema
LOGICAL DATA INDEPENDENCE:
Conceptual schema can be changed without affecting external schema
We change/modify conceptual schema when structure of database is altered
It is very difficult because, we have to see that the relationship must not changing, data is not getting lost and some other factors
It only provide immunity to external schema and application program