Ch 4

Question 1

Required attribute

Answer 1

A required attribute is an attribute that must have a value, i.e. it cannot be left empty.

Question 2

Optional attribute

Answer 2

An optional attribute is an attribute that does not need to have a value, i.e. it can be left empty.

Question 3

Identifiers

Answer 3

One or more attributes that uniquely identify each entity instance.

Question 4

Composite identifier

Answer 4

A primary key composed of more than one attribute.

Question 5

Composite attribute

Answer 5

A composite attribute, not to be confused with a composite key, is an attribute that can be further subdivided to yield additional attributes.

Question 6

Simple attribute

Answer 6

A simple attribute is an attribute that cannot be subdivided.

Question 7

Single-valued attribute

Answer 7

A single-valued attribute is an attribute that can only have a single value. E.g. social security numbers, serial numbers.

Question 8

Multivalued attributes

Answer 8

Multivalued attributes are attributes that can have many values. E.g. college degrees (you can have many different ones).

Question 9

Derived attribute

Answer 9

A derived attribute is an attribute whose value is derived (calculated) from other attributes.

Question 10

Participants

Answer 10

The entities that participate in a relationship are known as participants.

Question 11

Cardinality

Answer 11

Cardinality expresses the minimum and maximum number of entity occurrences associated with one occurrence of the related entity.

Question 12

Existence-dependency

Answer 12

An entity is said to be existence-dependent if it can exist in the database only when it is associated with another related entity occurrence.

Question 13

Existence-independence

Answer 13

If an entity can exist apart from all of its related entities, then it is existence-independent.

Question 14

Strong/regular entity

Answer 14

Entities that are existence-independent are strong (or regular) entities.

Question 15

Weak/non-identifying relationship

Answer 15

A weak relationship, 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.

Question 16

Strong/identifying relationship

Answer 16

A strong relationship, also known as an identifying relationship, exists when the primary key of the related entity contains a primary key component of the parent entity.

Question 17

Weak entity

Answer 17

A weak entity is one that meets two conditions:

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.

Question 18

Optional participation

Answer 18

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

Question 19

Mandatory participation

Answer 19

Mandatory participation means that one entity requires a corresponding entity occurrence in a particular relationship.

Question 20

Relationship degree

Answer 20

A relationship degree indicates the number of entities or participants associated with a relationship.

Question 21

Unary relationship

Answer 21

A unary relationship exists when an association is maintained within a single entity.

Question 22

Binary relationship

Answer 22

A binary relationship exists when two entities are associated.

Question 23

Ternary relationship

Answer 23

A ternary relationship exists when three entities are associated.

Question 24

Recursive relationship

Answer 24

A recursive relationship is one in which a relationship can exist between occurrences of the same entity set (naturally, such a condition is found within a unary relationship).

Question 25

Steps to build an ERD

Answer 25

1. Create detailed narrative of organization’s descriptions of operations.
2. Identify the business rules based on the description of operations.
3. Identify the main entities and relationships from the business rules.
4. Develop the initial ERD.
5. Identify attributes and primary keys that adequately describe the entities.
6. Revise and review the ERD.