Integrity Constraints Practice Questions

In database management systems, a locked file typically utilizes an exclusive lock to manage concurrency and ensure data integrity. When a process $P$ locks a database resource $R$, the system enforces mutual exclusion, denoted as $Lock(R, P)$. This constraint prevents concurrent access by other users, ensuring that $Access(R) = P$ holds true for the duration of the lock. Because other processes are blocked from accessing or modifying the resource, the file remains accessible to only the single user holding the lock. Thus, the database file is effectively restricted to access by only one user at a time.

The deletion of tuple $(2, 4)$ triggers a cascade because $C$ is a foreign key referencing $A$. First, we identify rows where $C = 2$, which results in the deletion of $(5, 2)$ and $(7, 2)$. Next, we check for a secondary cascade triggered by the deletion of these primary keys ($A=5$ and $A=7$). Checking the table for $C = 5$, we find the tuple $(9, 5)$ must also be deleted. Since no tuple contains $C = 7$ or $C = 9$, the process stops. Thus, the set of additionally deleted tuples is $(5, 2)$, $(7, 2)$, and $(9, 5)$.

Referential integrity requires that every foreign key value $d$ in relation $S$ must exist as a primary key value $a$ in relation $R$.

• Insert into S (II): If we insert a row into $S$ with a foreign key $d$ that does not exist in $R$, the constraint is violated.
• Delete from R (III): If we delete a row from $R$ whose primary key $a$ is currently referenced by some $d$ in $S$, the constraint is violated.
• Inserting into $R$ (I) adds a primary key and cannot violate the existence of existing foreign keys, while deleting from $S$ (IV) simply removes a reference, which does not violate the integrity of remaining data.
  Thus, operations II and III are the only ones that can cause a violation.