Logical Design

Question 1

What is a relation?

Answer 1

A relation is a two-dimensional table with specific characteristics. A table/entity may be a relation.

Question 2

What is the degree of a relation?

Answer 2

The number of columns in that relation.

Question 3

What is the cardinality of a relation?

Answer 3

The number of tuples or rows in that relation.

Question 4

What is a foreign key?

Answer 4

A foreign key is a key that refers to an attribute (or set of attributes) within a relation that matches a candidate key of another.

Question 5

T/F: Each cell of a relation should have (one/multiple) atomic values.

Answer 5

One

Question 6

T/F: Each attribute (may/must) have a distinct name.

Answer 6

Must

Question 7

T/F: A relation has a name that (is/is not) distinct from all other relation names in the database.

Answer 7

Is

Question 8

T/F: Each tuple (may be/is) distinct.

Answer 8

Is

Question 9

T/F: The order of attributes and tuples (has/has no) significance.

Answer 9

Has no

Question 10

What is the difference between a relation instance and a relation schema?

Answer 10

A relation instance is an single tuple/instance of data in that relation, while a relation schema is the definition of that relation, by its name and attributes.

Question 11

What are integrity constraints?

Answer 11

Integrity constraints are restrictions placed on the values of attributes.

Question 12

What is entity integrity?

Answer 12

Entity integrity means that no two tuples can have identical candidate key values, and that no attribute of a candidate key can be NULL.

Question 13

What is referential integrity?

Answer 13

Referential integrity means that if a foreign key exists within a relation, either the foreign key value matches a primary key value in its home relation, or the foreign key value is NULL.

Question 14

What is a domain constraint?

Answer 14

A domain constraint allows the RDBMS to carry out checks on data errors and determine the range of operations that can be carried out in the domain.

Question 15

What is a view?

Answer 15

A view is a virtual subset of a base relation.

Question 16

How may we model a one-to-many binary relationship in a logical design?

Answer 16

In a one-to-many relationship, the foreign key must be placed on the many side. This is so that we can give each “many” a reference back to the “one”.

Question 17

How may we model a one-to-one binary relationship in a logical design?

Answer 17

In a one-to-one relationship, our modelling depends on which side is mandatory. We must place a foreign key on any table that is considered mandatory for the database.

In the case that both sides are optional, we can decide which side to place it on.

Question 18

How may we model a many-to-many binary relationship in a logical design?