Chapter 4 - Entity Relationship (ER) Modeling

iterative process

A process based on repetition of steps and procedures.

existence-dependent

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

weak relationship

A relationship that exists when the PK of the related entity does not contain a PK component of the parent entity. Also known as a non-identifying relationship.

identifying relationship

A relationship that exists when the related entities are existence-dependent. Also called a strong relationship or strong identifying relationship because the dependent entity's primary key contains the primary key of the parent entity.

recursive relationship

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

non-identifying relationship

A relationship that occurs when the primary key of the dependent (many side) entity does not contain the primary key of the related parent entity. Also known as a weak relationship.

mandatory participation

A term used to describe a relationship in which one entity occurrence must have a corresponding occurrence in another entity. Example: EMPLOYEE works in DIVISION. (A person cannot be an employee if he or she is not assigned to a company's division.)

ternary relationship

An ER term used to describe an association (relationship) between three entities. Example: A CONTRIBUTOR contributes money to a FUND from which a RECIPIENT receives money.

binary relationship

An ER term used to describe an association (relationship) between two entities. Example: PROFESSOR teaches COURSE.

unary relationship

An ER term used to describe an association within an entity. Example: A COURSE is a prerequisite to another COURSE.

participants

An ER term used to label the entities that participate in a relationship. Example: PROFESSOR teaches CLASS. (The teaches relationship is based on the participants PROFESSOR and CLASS.)

composite attribute

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

multivalued attribute

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.

single-valued attribute

An attribute that can have only one value.

simple attribute

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

derived attribute

An attribute that does not physically exist within the entity and is derived via an algorithm. Example: Age = current date - birth date.

existence-independent

An entity that can exist apart from one or more related entities. It must be created first when referencing an existence-dependent table to it.

weak entity

An entity that displays existence dependence and inherits the primary key of its parent entity. Example: A DEPENDENT requires the existence of an EMPLOYEE.

cardinality

Assigns a specific value to connectivity. Expresses the range (minimum to maximum) of allowed entity occurrences associated with a single occurrence of the related entity.

connectivity

Describes the classification of the relationship between entities. Classifications include 1:1, 1:M, and M:N.

composite identifier

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

optional participation

In ER modeling, refers to a condition where one entity occurrence does not require a corresponding entity occurrence in a particular relationship.

optional attribute

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

required attribute

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

relationship degree

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

identifiers

The ERM uses identifiers to uniquely identify each entity instance. In the relational model, such identifiers are mapped to primary keys in tables.

strong relationship

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