Can some please explain little elaborately why it is difficult to achieve logical data independence.
So for logical data independence, any changes at the logical levels have to be such that you also have to adapt the user views so that they still produce the same result as before. This way the users that access these views will not notice the changes in the logical data model. To do this you need full support for both updates and queries over views, but most DMBS implementations do not fully support this. So you have limited support for independence and changes to the logical schema can cause your views to become un-updateable.
There is also the issue that not all updates over views have an intuitive translation to updates over the base tables.