Database Management 8

Question 1

Computing a derived attribute can be as simple as adding two attribute values located on the same row, or it can be the result of aggregating the sum of values located on many table rows (from the same table or from a different table).

Answer 1

info …

Question 2

The entities that participate in a relationship are also known as participants, and each relationship is identified by a name that describes the relationship. The relationship name is an active or passive verb; for example, a STUDENT takes a CLASS, a PROFESSOR teaches a CLASS etc …

*** connectivity is used to describe the relationship classification.

Answer 2

info …

Question 3

expresses the minimum and maximum number of entity occurrences associated with one occurrence of the related entity. In the ERD, cardinality is indicated by placing the appropriate numbers beside the entities, using the format (x,y). The first value represents the minimum number of associated entities, while the second value represents the maximum number of associated entities.

Answer 3

Cardinality

Question 4

denotes an instance of a specific entity is optional or mandatory in a relationship. For instance an open order must have a customer associated with it, but every customer does not need to have an open order. Modality is expressed with a straight line for modality 1 or a circle for modality 0.

Answer 4

Modality

Question 5

refers to the minimum number of times an instance of an entity can be associated with an instance in a related entity while cardinality refers to the maximum number of times this relationship may occur.

Answer 5

Modality

Question 6

if it can exist in the database only when it is associated with another related entity occurrence. an entity is existence-dependent if it has a mandatory foreign key—that is, a foreign key attribute that cannot be null.

*** If an entity can exist apart from all of its related entities, then it is existence-independent, and it is referred to as a strong entity or regular entity.

Answer 6

existence-dependent

Question 7

is based on how the primary key of a related entity is defined. To implement a relationship, the primary key of one entity (the parent entity, normally on the “one” side of the one-to-many relationship) appears as a foreign key in the related entity (the child entity, mostly the entity on the “many” side of the one-to- many relationship).

Answer 7

The concept of relationship strength

Question 8

also known as a non-identifying relationship, exists if the primary key of the related entity does not contain a primary key component of the parent entity. By default, relationships are established by having the primary key of the parent entity appear as a foreign key (FK) on the related entity (also known as the child entity).

Answer 8

Weak Relationship

Question 9

exists when the primary key of the related entity contains a primary key component of the parent entity.

Answer 9

strong (identifying) relationship

Question 10

(1) The entity is existence-dependent; it cannot exist without the entity with which it has a relationship. (2) The entity has a primary key that is partially or totally derived from the parent entity in the relationship.

Answer 10

Weak Entity