(2) (a) Define the terms Candidate key and Primary key. () (b) With the aid of example relations, explain what Referential Integrity is, and how the options RESTRICT and CASCADE are applied when a referenced tuple is updated or deleted. (6) (c) Describe, in the context of a database, what a Transaction is. Your an- swer should discuss each of the ACID properties and how these prop- erties are ensured by the Database Management system (DBMS). (6) (d) Given the 3 relations below (Student, Grade, Module): SID 1 1 Student SID Name 1 Alex 2 Ben 3 Carl 4 Drew 1 Grade mCode AE1PRG AE1DBS AE1FUN AE1DBS AE1PRG AE1FUN AE1PRG Mark 60 65 70 75 80 50 50 Module mCode Title AE1PRG Programming AE1DBS Databases AEIUST Unix AE1FUN Haskell 2 2 3 3 Write the results for the following relational algebra expressions. Note:: The notation used below is as such: 0 :: Selection; 1 :: Projection; U :: Union; n :: Intersection; - :: Set Difference; X :: Cartesian Product. (i) TimCode (Grade) (ii) OsID=1(Grade) (1) (iii) 1 31D(Student) U T IDO Mark>=80(Grade) (2) (iv) Translate the following SQL query into relational algebra (using only 0,7, X operators): (4) as @ 13 SELECT Name, Title, Mark FROM Student NATURAL JOIN Grade NATURAL JOIN Module