Relationships

Question 1

What is a one-to-one relationship?

Answer 1

A one-to-one relationship is where each record in one table is related to exactly one record in another table.

Question 2

What is a one-to-many relationship?

Answer 2

A one-to-many relationship is where each record in one table is related to many records in another table.

Question 3

What is a many-to-many relationship?

Answer 3

A many-to-many relationship is where each record in one table can be related to many records in another table, and vice versa.

For example, a student may be taught by multiple professors, and a professor may be teaching multiple students.

Question 4

What is the cardinality of a relationship?

Answer 4

The cardinality of the relationship is the maximum values for the multiplicity ranges on either side of the relationship.

e.g. If a relationship is 1:4, the cardinality is 4, because we may have at maximum 4 on the largest side.

Question 5

What is the participation of a relationship?

Answer 5

The minimum values for the multiplicity ranges on either side of the relationship.

e.g. If a relationship is 1:4, the participation is 4, because we need at least 1 to participate.

Question 6

What is meant by the multiplicity constraints of a relationship?

Answer 6

How many or how little of that entity must exist for the relationship to be valid.

e.g. An entity with multiplicity constraints 0..1 implies that the entity may or may not exist, while one that is 1..4 implies that there must be between 1 and 4 of that entity.

Question 7

What is a connection trap in a database?

Answer 7

A connection trap occurs when a pathway between two entities is either ambiguous or false existent.

Question 8

What is the difference between a fan and chasm connection trap?

Answer 8

A fan trap occurs when a path between certain entity occurrences is ambiguous, while a chasm trap occurs when it does not exist at all.

Question 9

How may we most efficiently begin to conceptually design a database?

Answer 9

We start by identifying the types of entity and relationships, to give a purely conceptual model to connect our entities.

Then, we may identify any attributes and the primary keys of that entity.

We may then check for multiplicity constraints and traps, then validate the model against user transactions, finally reviewing it with the end user.