Entity Relationship Model Concept

These flashcards cover the fundamental concepts of Entity Relationship (ER) Modeling, including components, symbols, attribute types, relationship degrees, cardinality, participation constraints, and the distinction between strong and weak entities.

Entity-Relationship (E-R) Model

A way to represent real-world data in a form that is easy to understand and design for databases by mapping real-world enterprise interactions into a conceptual schema.

Conceptual Schema

A blueprint of how data will be structured within a database system.

ER Diagram (ERD)

A diagram that displays the relationship of entity sets stored in a database to help explain the logical structure.

Entity

A person, place, object, event, or concept in the real world with an independent existence.

Entity Set

A collection of similar entities that share common properties or characteristics.

Attributes

Properties that describe an entity, such as the name, age, and gender of a student.

Rectangle (ER Symbol)

The symbol used to represent Entities in an ER Model.

Ellipse (ER Symbol)

The symbol used to represent Attributes in an ER Model.

Diamond (ER Symbol)

The symbol used to represent Relationships among Entities.

Lines (ER Symbol)

The symbol used to represent links between attributes to entities and entity sets with other relationship types.

Double Ellipse (ER Symbol)

The symbol used to represent Multi-Valued Attributes in an ER Model.

Double Rectangle (ER Symbol)

The symbol used to represent a Weak Entity in an ER Model.

Simple Attribute

An attribute that cannot be broken down into component parts.

Composite Attribute

Attributes that can be divided into smaller subparts which represent more basic attributes with independent meaning, such as an address being divided into street and city.

Multi-valued Attribute

An attribute consisting of more than one value for a given entity, such as multiple phone numbers for a single student.

Key Attribute

A minimal set of attributes whose values uniquely identify an entity in a set, represented in an ER diagram with the name underlined inside an oval.

Derived Attribute

Attributes that contain values calculated from other attributes, such as age being calculated from a birthdate.

Stored Attribute

An attribute used to calculate a derived attribute, such as Birthdate being used to determine Age.

Relationship

A meaningful association between and among entity types, normally named using a verb or verb group.

Domain (Value Set)

A set of possible values that can be stored in a column of a database table, usually defined by a data type (e.g., an INTEGER type or an age range of $0-120$).

Null Value

A value used in a relational database when a column value is unknown or missing; it is neither an empty string nor a zero value.

Degree of a Relationship

The number of participating entity types in a relationship type.

Unary Relationship

An association involving only one entity type, also known as a relationship of $\text{Degree } 1$, such as a person being married to another person.

Binary Relationship

An association among two entity types, categorized as a relationship of $\text{Degree } 2$.

Ternary Relationship

A relationship of $\text{Degree } 3$ where three entities participate simultaneously.

N-ary Relationship

A simultaneous relationship among instances of four or more entity types, categorized as $\text{Degree } 4$ or higher.

Cardinality Ratio

Specifies the maximum number of relationship instances that an entity can participate in (e.g., $1:1$, $1:N$, or $M:N$).

One-to-One ($1:1$) Relationship

A relationship where each entity in set A is related to at most one entity in set B, and vice versa.

One-to-Many ($1:N$) Relationship

A relationship where one entity in the first set can be related to multiple entities in the second set, but each entity in the second set relates to only one in the first.

Many-to-Many ($M:N$) Relationship

A relationship where entities in all participating entity sets can take part more than once.

Participation Constraint

Defines how entities participate in a relationship, specifically whether the existence of an entity depends on its association with another entity.

Total Participation

A constraint where every entity in an entity set must participate in at least one relationship instance; represented by a double line.

Partial Participation

A constraint where the entities in an entity set may or may not participate in the relationship; represented by a single line.

Weak Entity

An entity that does not have key attributes of its own and depends on another entity for unique identification.

Strong (Regular) Entity

An entity that has a key attribute and exists independently of other entity types in the schema.

Partial Key

Attributes that, in conjunction with the primary key of another entity, uniquely identify a weak entity.