vault backup: 2024-04-16 16:47:25

Semester 2/Database Systems/Trimester 2 Assignment.md

@@ -24,7 +24,7 @@ If the "street" attribute is unneeded, less IO operations are needed to retrieve
 #### i)
 
 ![](Pasted%20image%2020240415135455.png)
-
+# Add Projections
 #### ii)
 
 Root Node: $\pi$ ( factory.name )
@@ -41,32 +41,30 @@ Line-by-line:
 
 # Q2
 
-# **a)**
+### a)
 
-*Consistency: Database should be in a consistent state, prior to a transaction and after. e.g. Following constraints, relationships, etc.
-Isolation: All transactions should by fully independent from concurrently executing transactions.
-Durability: When a transaction is committed, it's effect should be permanent in the database, withstanding system failures or restarts.*
-
-*Atomicity: A transaction must be completed, or aborted. If a transaction fails, a DBMS ensures the rollback of data to allow the database to remain consistent.
-Consistency: A DBMS would enforce constraints on a transaction, assuring the defined rules / relationships are followed.
-Isolation: Reduces concurrency issues by restricting access to shared data until a transaction is committed.
-Durability: Guarantees data is permanent once committed, preventing inconsistency after failures.*
+Atomicity: A transaction must be completed, or aborted. If a transaction fails, a DBMS ensures the rollback of data to allow the database to remain consistent.
+Consistency: Database should be in a consistent state, prior to a transaction and after. A DBMS would enforce constraints on a transaction, assuring the defined rules / relationships are followed.
+Isolation: All transactions should by fully independent from concurrently executing transactions. Reduces concurrency issues by restricting access to shared data until a transaction is committed.
+Durability: Guarantees data is permanent once committed, preventing inconsistency after failures. Should withstand system failures or restarts.
 
 ### b)
 
 To guarantee consistency, a DBMS handles the enforcement of atomicity, consistency, isolation and durability, along with concurrency control to prevent conflicts.
-Transfer of crates:
+
+Ideal SQL Transfer of crates:
 
 ```sql
-UPDATE warehouses
+UPDATE warehouse
 SET crates = crates - 3
 WHERE wname = 'warehouse1'
 
-UPDATE warehouses
+UPDATE warehouse
 SET crates = crates + 3
 WHERE wname = 'warehouse2';
 ```
 
+If the second query is not run, it is not the fault of the DBMS. A DBMS can only enforce ACID rules and ensure consistency, not transaction logic.
 ### c)
 
 By allowing concurrent execution of transactions, system resources are allocated more efficiently due to multiple operations occurring simultaneously. This has an effect of being more performant, since more transactions can be processed per second.
@@ -114,7 +112,7 @@ Deadlock does not occur, since there are no cycles in the graph
 ### d)
 
 #### i)
-
+# TO DO
 The recovery manager would first identify in-progress transactions at the time of failure
 
 # Q4
@@ -132,5 +130,45 @@ WHERE partPrice > 100;
 #### ii)
 
 ```sql
-SELECT 
+SELECT carModel
+FROM car
+JOIN carPart ON car.carId = carPart.carId
+GROUP BY car.carModel
+HAVING COUNT(carPart.partID) > 4;
 ```
+
+
+### b)
+
+If the DBA revoked auth from U2 -> U1, U4, and U5 would also have auth revoked due to cascading revokes. There is no path from U1, U4 or U5 to the DBA if U2's authorisation is revoked. U3 and U6 still have a path to the DBA, as they do not depend on U2 for authorisation, authorisation is still valid.
+
+### c)
+
+#### i)
+
+```sql
+GRANT ALL PRIVILEGES ON * TO Isavella
+
+CREATE VIEW employeeView AS
+	SELECT *
+	FROM employee
+
+GRANT SELECT, UPDATE ON employeeView TO Laura, Naser;
+```
+
+#### ii)
+
+```sql
+CREATE VIEW projectsView AS
+	SELECT *
+	FROM project
+	WHERE level = 'advanced'
+
+GRANT SELECT ON projectsView TO Jane;
+```
+
+#### iii)
+
+```SQL
+REVOKE ALL PRIVILEGES ON * FROM Naser;
+```