Phase 2 Checkpoint (15 questions)

15 questions · 24 marks · 40 minutes. Negative marking on MCQ only: −1/3 mark for a wrong 1-mark MCQ, −2/3 for a wrong 2-mark MCQ. No negative marking for MSQ or NAT; MSQ has no partial credit.

Q1 · NAT · 1 mark(s) — Degree

A relation has attributes (a, b, c, d) and 50 tuples. What is its degree?

Numerical answer: ________

Q2 · MCQ · 1 mark(s) — Properties

Which is true in the relational model?

1. (A) Every value is atomic or NULL
2. (B) A relation may contain duplicate tuples
3. (C) Attributes must have numeric domains
4. (D) Tuples are ordered by primary key

Q3 · NAT · 2 mark(s) — NULL

Column x: 3, NULL, 3, 8, NULL, 1. How many rows satisfy NOT (x = 3)? (NOT of UNKNOWN is UNKNOWN.)

Numerical answer: ________

Q4 · NAT · 2 mark(s) — Superkeys

R(A, B, C, D, E, F) has candidate keys {A, B} and {A, C}. How many superkeys?

Numerical answer: ________

Q5 · MCQ · 2 mark(s) — Keys

Instance of R(A, B, C): (1, a, x), (2, a, y), (3, b, x), (4, b, y). Which can be a candidate key based on this instance?

1. (A) {B}
2. (B) {C}
3. (C) {B, C}
4. (D) {A, B}

Q6 · MSQ · 2 mark(s) — Foreign keys

Which are allowed for a foreign key FK in R₁ referencing R₂'s primary key?

1. (A) An FK value missing from R₂
2. (B) The same FK value in many tuples of R₁
3. (C) FK referencing R₁ itself
4. (D) FK value NULL (FK not part of R₁'s PK)

Q7 · MCQ · 1 mark(s) — Constraints

Updating the cgpa of a student (non-key, non-FK) can violate:

1. (A) domain constraint
2. (B) key constraint
3. (C) entity integrity
4. (D) referential integrity

Q8 · MSQ · 2 mark(s) — Constraints

Which operations can never violate referential integrity?

1. (A) Inserting into the referencing relation
2. (B) Inserting into the referenced relation
3. (C) Deleting from the referenced relation
4. (D) Deleting from the referencing relation

Q9 · NAT · 2 mark(s) — Cascade

R(A, B) with B → R.A ON DELETE CASCADE: (1, NULL), (2, 1), (3, 1), (4, 2), (5, 4), (6, 3), (7, NULL), (8, 7). Delete A = 2. How many tuples remain?

Numerical answer: ________

Q10 · MCQ · 2 mark(s) — Set null

Same R but ON DELETE SET NULL. Delete A = 1. Which tuples change?

1. (A) (2, 1) and (3, 1) become (2, NULL) and (3, NULL)
2. (B) (2, 1), (3, 1), (4, 2), (6, 3) all change
3. (C) all tuples are deleted
4. (D) nothing; the delete is rejected

Q11 · MCQ · 1 mark(s) — Mapping

A composite attribute is mapped to:

1. (A) a foreign key
2. (B) a separate table
3. (C) its simple components as columns
4. (D) a multivalued column

Q12 · NAT · 1 mark(s) — Minimum tables

E1 —M:N— E2, where E1 has 1 multivalued attribute. Minimum tables?

Numerical answer: ________

Q13 · NAT · 2 mark(s) — Minimum tables

E1 —1:N— E2 —1:1 (both total)— E3, E2 is a weak entity owned by E1 through the 1:N relationship. Minimum tables?

Numerical answer: ________

Q14 · MCQ · 2 mark(s) — Ternary

A ternary relationship R(E1, E2, E3) with all sides many and no attributes needs:

1. (A) one table whose PK is the three keys together
2. (B) no table; FKs are added to the entity tables
3. (C) one table whose PK is E1's key
4. (D) three tables, one per pair

Q15 · MCQ · 1 mark(s) — Specialisation

A total, disjoint specialisation of ACCOUNT into SAVINGS and CURRENT can be mapped without NULLs and without a superclass table using:

1. (A) one table with flags
2. (B) superclass table only
3. (C) one table with a type attribute
4. (D) subclass tables only