1) If we consider knowing the availability of data is a type of
Yes, knowing the availability of data is a type of confidentiality violation. Example is error message revealing whether a username exists or not in the database.
2) What is the referential integrity problem in database security?
For database elements to be consistently synchronized, multiple tables which segregates data about a single attribute has to be linked properly. In otherwords, no rogue data set should exist.
Suppose I have an application with two database tables
user_credentials has columns
Referential integrity is the property by which both the tables have exactly all the same values in
user_name field. This ensures consistency in accessing or removing the table elements.
3) Can confidentiality violation lead to integrity violation?
It is possible. But both has to be considered separately. Consider a scenario where a broken hashing algorithm with a known collission is used. Knowledge about the broken algorithm can be used to bypass the integrity checks. But from an Information security perspective theintegrity violation happens because of the use of a broken algorithm, though it is a result of confidentiality compromise.