L7 Integrity Contraints

Question 1

What are integrity contraints?

Answer 1

Integrity constraints are logical statements that restrict the set of allowable relations in a database.

Question 2

What is the relationship between Keys and Functional Dependencies (FD)?

Answer 2

Keys are special cases of Functional Dependencies (FDs).

for instance: Stating that DNAME is a key of DEPT, means that no two distinct tuples in r2 have the same DNAME.

Question 3

What are inclusion dependencies?

Answer 3

The existence of attributes in a table R whose values must be a subset of the values of the corresponding attributes in another table S

Question 4

What is the relationship between Foreign Keys and Inclusion Dependencies?

Answer 4

Foreign keys are special cases of Inclusion dependencies (IND).

Question 5

What is a foreign key?

Answer 5

A foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table

Question 6

What are data dependencies?

Answer 6

Constraints that depend on the equality or inequality of values in tuples of relations are called data dependencies.

Question 7

Name two examples of data dependencies.

Answer 7

FDs and INDs are data dependencies

Question 8

What are domain dependencies?

Answer 8

Constraints that restrict the allowable domain values are called domain dependencies (DDs)

Question 9

Name an example of a domain dependency (DD).

Answer 9

• An example of a DD is that SALARY ranges between 15 and 40.
• Another example of a DD is that ENAME is a string of at most 25 characters.

Question 10

What are cardinality constraints?

Answer 10

Constraints that restrict the cardinality of a projection of a relation onto a set of attributes are called cardinality constraints (CCs)

Question 11

What are cardinality contstraints (CC)?

Answer 11

Constraints that restrict the cardinality of a projection of a relation onto a set of attributes are called cardinality constraints (CCs)

Question 12

Name an example of a cardinality constraint (CC)?

Answer 12

• An example of a CC is that there should not be more managers than employees.
• Another example of a CC is that the number of students doing the MSc course should not exceed 100.

Question 13

What is a functional dependency?

Answer 13

An FD over R is a statement of the form R: X →Y where X and Y are subsets of schema(R).

We say that X functionally determines Y .

An FD X → Y is satisfied in a relation r, if whenever two rows in r have the same X -value they also have the same Y -value.

An FD X → Y is satisfied in a relation r , if for each X -value of r there is at most one Y -value.