Databse Management 9

Question 1

means that one entity occurrence does not require a corresponding entity occurrence in a particular relationship.

Answer 1

Optional Participation

Question 2

means that one entity occurrence requires a corresponding entity occurrence in a particular relationship. If no optionality symbol is depicted with the entity, the entity is assumed to exist in a mandatory relationship with the related entity. If the mandatory participation is depicted graphically, it is typically shown as a small hash mark across the relationship line. The existence of a mandatory relationship indicates that the minimum cardinality is at least 1 for the mandatory entity.

Answer 2

Mandatory Participation

Question 3

indicates the number of entities or participants associated with a relationship. A unary relationship exists when an association is maintained within a single entity. A binary relationship exists when two entities are associated. A ternary relationship exists when three entities are associated. Although higher degrees exist, they are rare and are not specifically named.

Answer 3

Relationship Degree

Question 4

is one in which a relationship can exist between occurrences of the same entity set.

Answer 4

Recursive Relationship

Question 5

partial dependency exists when there is a functional dependence in which the determinant is only part of the primary key.

A transitive dependency exists when there are functional dependencies such that X → Y, Y → Z, and X is the primary key. In that case, the dependency X → Z is a transitive dependency because X determines the value of Z via Y.

Answer 5

partial / transitive dependency

Question 6

derives its name from the fact that a group of multiple entries of the same type can exist for any single key attribute occurrence.

Answer 6

repeating group