Constrainsts in Databases

Question 1

A ________ is a relationship among data elements that the DBMS is required to enforce

Answer 1

constraint

Question 2

What are 5 types of constraints?

Answer 2

• Functional Dependencies
• Inclusion Dependencies
• Value-based constraints
• Tuple-based constraints
• Assertions

Question 3

DB instances that satisfy all constraints are called _____

Answer 3

legal

Question 4

Many kinds of constraints can expressed in ____

Answer 4

RA

Question 5

What is an equivalent way to represent R (subset) S?

Answer 5

R-S = (empty set)

Question 6

What is an equivalent way to represent R = (empty set)?

Answer 6

R (subset) (empty set)

Question 7

_______________ style of expressing constraints is common in SQL

Answer 7

equal-to-emptyset

Question 8

Give examples of a domain constraint on an attribute

Answer 8

Integers only/ strings of length 20

Question 9

What is a key constraint?

Answer 9

A set of attributes for a relation that does not allow 2 tuples in a relation instance to have the same values

Question 10

What is a foreign-key constraint?

Answer 10

A value appearing in the attribute(s) of one relation must also appear as a value in attribute(s) that are a key of another relation

Question 11

(Foreign) Key constraints are special cases of ____________ dependencies and ___________ dependencies

Answer 11

functional, inclusion

Question 12

________ dependencies are constraints in the form X -> Y where X, Y are sets of attributes

Answer 12

functional

Question 13

In FDs, the values of X ________ the values of Y

Answer 13

determines

Question 14

Why are relation keys are special case of the FD X->Y?

Answer 14

Y is just the whole set of attributes of a relation when determining a key

Question 15

What form do INDs take?

Answer 15

Constraints of the form R[X] (subset) S[Y]

Question 16

For INDs, the _______ of attributes matter

Answer 16

order

Question 17

INDs are _________ constraints, meaning they link the contents of one table to another table

Answer 17

referrential

Question 18

When does a set of constraints imply or entail a single constraint?

Answer 18

When every instance that satisfies the set of constraints also satisfies the single constraint

Question 19

What is the notation of an implication of constraints?

Answer 19

Σ |= φ

Question 20

A _______ axiomatization implies every derived constraint

Answer 20

sound

Question 21

A ______ axiomatization can derive implied constraints

Answer 21

complete

Question 22

Σ |= φ IFF Σ |- φ

Answer 22

Σ |= φ IFF Σ |- φ

Question 23

If Y (subset) X, then…

Answer 23

X -> Y

Question 24

If X -> Y, then…

Answer 24

XZ -> YZ for any Z

Question 25

If X -> Y and Y -> Z, then

Answer 25

X -> Z

Question 26

If X -> Y and X -> Z, then…

Answer 26

X -> YZ

Question 27

If X -> YZ, then…

Answer 27

X -> Y and X -> Z

Question 28

The ________ F+ of F is the set of all FDs implied by the FDs in F

Answer 28

closure

Question 29

A closure can be computed using ________ axioms

Answer 29

Armstrong’s

Question 30

Compute the closure of F = { A -> B, B -> C}

Answer 30

F+ = F U {A -> C, AC -> BC, AB -> AC, AB -> BC} U {all trivial FDs on A, B, C}