(4) The Relational Model of Data

Question 1

Relationship degree

Answer 1

The number of entities or participants associated with a relationship. A relationship degree can be unary, binary, ternary, or higher.

Question 2

Optional attribute

Answer 2

In ER modeling, an attribute that does not require a value; therefore, it can be left empty.

Question 3

Binary relationship

Answer 3

An ER term for an association (relationship) between two entities. For example, PROFESSOR teaches CLASS.

Question 4

Strong entity

Answer 4

An entity that is existence-independent, that is, it can exist apart from all of its related entities. Also called regular entity.

Question 5

Iterative process

Answer 5

A process based on repetition of steps and procedures.

Question 6

Participants

Answer 6

An ER term for entities that participate in a relationship. For example, in the relationship “PROFESSOR teaches CLASS,” the teaches relationship is based on the participants PROFESSOR and CLASS.

Question 7

Existence-independent

Answer 7

A property of an entity that can exist apart from one or more related entities. Such a table must be created first when referencing an existence-dependent table.

Question 8

Identifiers

Answer 8

One or more attributes that uniquely identify each entity instance.

Question 9

Composite attribute

Answer 9

An attribute that can be further subdivided to yield additional attributes. For example, a phone number such as 615-898-2368 may be divided into an area code (615), and exchange number (898), and a four-digit code (2368). Compare to simple attribute.

Question 10

Weak relationship

Answer 10

A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.

Question 11

Ternary relationship

Answer 11

An ER term used to describe an association (relationship) between three entities. For example, a DOCTOR prescribes a DRUG for a PATIENT.

Question 12

Existence-dependent

Answer 12

A property of an entity whose existence depends on one or more other entities. In such an environment, this table must be created and loaded first because the existence-dependent key cannot reference a table that does not yet exist.

Question 13

Multi valued attributes

Answer 13

An attribute that can have many values for a single entity occurrence. For example, an EMP_DEGREE attribute might store the string “BBA, MBA, PHD” to indicate three different degrees held.

Question 14

Mandatory participation

Answer 14

A relationship in which one entity occurrence must have a corresponding occurrence in another in tiny. For example, an EMPLOYEE works in a DIVISION. (A person cannot be an employee without being assigned to a company’s division).

Question 15

Cardinality

Answer 15

A property that assigns a specific value to connectivity and expresses the range of allowed entity occurrences associated with a single occurrence of the related entity.

Question 16

Simple attribute

Answer 16

An attribute that cannot be subdivided into meaningful components. Compare to composite attribute.

Question 17

Required attribute

Answer 17

In ER modeling, an attribute that must have a value. In other words, it cannot be left empty.

Question 18

Non-identifying relationship

Answer 18

A relationship in which the primary key of the related entity does not contain a primary key component of the parent entity.

Question 19

Single-valued attribute

Answer 19

An attribute that can have only one value.

Question 20

recursive relationship

Answer 20

A relationship found within a single entity type. For example, an EMPLOYEE is married to an EMPLOYEE or a PART is component of another PART.

Question 21

Unary relationship

Answer 21

An ER term to describe an association within an entity. For example, and EMPLOYEE might manage another EMPLOYEE.

Question 22

Strong (identifying) relationship

Answer 22

A relationship that occurs when two entities are existence-dependent; from a database design perspective, this relationship exists whenever the primary key of the related entity contains the primary key of the parent entity.

Question 23

Optional participation

Answer 23

In ER modeling, a condition in which one entity occurrence does not require a sores pounding entity occurrence in a particular relationship.

Question 24

Weak entity

Answer 24

An entity that displays existence dependence and inherits the primary key of its parent entity. For example, a DEPENDENT requires the existence of an EMPLOYEE.

Question 25

Composite identifier

Answer 25

In ER modeling, a key composed of more than one attribute.

Question 26

Derived attribute

Answer 26

An attribute that does not physically exist within the entity and is derived via an algorithm. For example, the Age attribute may be derived by subtracting the birth date from the current date.

Question 27

Relational schema

Answer 27

The organization of a relational database as described by the database administrator.