Entity-Relationship Modeling Essentials

Vocabulary flashcards covering core terms, constraints, traps, and enhanced concepts of Entity-Relationship and Enhanced ER modeling.

Entity

A thing or object in the environment that the organization wants to keep data about.

Entity Set

A collection of entities of the same type (e.g., all employees).

Entity Type

A group of objects with the same properties that the enterprise recognizes as having independent existence.

Entity Occurrence

A uniquely identifiable instance of an entity type.

Relationship Type

A named set of meaningful associations among two or more entity types.

Relationship Occurrence

A uniquely identifiable association that includes one occurrence from each participating entity type.

Binary Relationship

A relationship of degree two involving exactly two entity types.

Ternary Relationship

A relationship of degree three involving three different entity types.

Quaternary Relationship

A relationship of degree four involving four different entity types.

Recursive Relationship

A relationship where the same entity type participates more than once in different roles.

Attribute

A property or characteristic describing an entity.

Primary Key (PK)

An attribute, or set of attributes, whose values uniquely identify each entity occurrence.

Attribute Domain

The set of allowable values for an attribute.

Simple Attribute

An attribute composed of a single, indivisible component (e.g., Salary).

Composite Attribute

An attribute made up of multiple components, each with independent meaning (e.g., Address → Street, City, Postcode).

Single-Valued Attribute

An attribute that holds exactly one value for each entity occurrence.

Multi-Valued Attribute

An attribute that can hold multiple values for a single entity occurrence (e.g., multiple phone numbers).

Derived Attribute

An attribute whose value is calculated from other attributes (possibly in different entity types).

Strong Entity Type

An entity type that is not existence-dependent on any other entity type.

Weak Entity Type

An entity type that is existence-dependent on another entity type.

Attribute on Relationship

A property that belongs to a relationship type rather than to either participating entity (later modeled as a bridge entity).

Multiplicity

The number or range of possible occurrences of one entity that can relate to a single occurrence of another through a relationship (business rule).

Cardinality (in Multiplicity)

The maximum number of relationship occurrences for an entity in a given relationship type.

Participation (in Multiplicity)

Whether all (mandatory) or only some (optional) entity occurrences take part in a relationship.

One-to-One (1:1) Relationship

Each occurrence of both entity types relates to at most one occurrence of the other.

One-to-Many (1:*) Relationship

One entity occurrence relates to many occurrences of another, but the reverse is at most one.

Many-to-Many (:) Relationship

Entity occurrences on both sides can relate to many occurrences of the other.

Fan Trap

A connection trap where a path between entity occurrences is ambiguous due to misinterpreted relationships.

Chasm Trap

A connection trap where a model implies a relationship path that does not exist between certain entity occurrences.

Enhanced ER (EER) Model

An extension of the ER model that adds semantic concepts like specialization and generalization.

Superclass

An entity type that contains one or more distinct subgroupings (subclasses) of its occurrences.

Subclass

A distinct subgrouping of occurrences of a superclass entity type.

Attribute Inheritance

The property whereby a subclass entity inherits all attributes of its superclass and may add its own.

Specialization

The process of maximizing differences by identifying distinguishing characteristics among entity occurrences to form subclasses.

Generalization

The process of minimizing differences by identifying common characteristics to form a superclass.

Participation Constraint (in EER)

Specifies whether every superclass member must belong to at least one subclass (mandatory) or not (optional).

Disjoint Constraint

Specifies whether a superclass member can belong to only one subclass (disjoint) or multiple subclasses (nondisjoint/overlapping).