Key Concepts in Database Design and Relationships

Associative Entity

An entity used to represent a many-to-many relationship between two or more entities. Also known as a Composite Entity or a Bridge Entity (pg 94)

Attribute

A characteristic or property of an entity. (pg 36)

Associative Entity

An entity used to represent a many-to-many relationship between two or more entities. Also known as a Composite Entity or a Bridge Entity (pg 94)

Attribute

A characteristic or property of an entity. (pg 36)

Attribute Domain

The set of allowable values for an attribute. (pg 70)

Binary Relationship

A relationship between two entities. (pg 132)

Bridge Entity

Another term for an associative entity. Also known as a Composite Entity or a Associative Entity (pg 94)

Business Rule

A brief, precise, and unambiguous description of a policy, procedure, or principle within a specific organization. (pg 37)

Candidate Key

A minimal superkey—that is, a superkey without any unnecessary attributes (pg 73)

Cardinality

Expresses the minimum and maximum number of entity occurrences associated with one occurrence of the related entity. (pg 121)

Chen Notation

A type of entity-relationship diagram notation that uses rectangles to represent entities and diamonds to represent relationships and favors conceptual modeling. (pg 45)

Composite Attribute

An attribute that can be subdivided into other attributes. (pg 116)

Composite Entity

An entity designed to transform an M:N relationship into two 1:M relationships. Also known as a Associative Entity or a Bridge Entity (pg 94)

Composite Identifier

Another term for a Composite Key.

Composite Key

A key that is composed of more than one attribute. (pg 73)

Connectivity

The classification of the relationship between entities. (pg 121)

Constraint

A rule that restricts the values in a database.

Crow's Foot Notation

A type of entity-relationship diagram notation that uses symbols to represent the cardinality of relationships. (pg 45)

Data Dictionary

A repository of information that provides a detailed description of all tables in the database created by the user and designer. (pg 87)

Data Model

A relatively simple representation, usually graphical, of more complex real-world data structures. (pg 35)

Data Modeling

The process of creating a specific data model for a determined problem domain. (pg 35)

Dependent

An attribute whose value is determined by another attribute. (pg 72)

Derived Attribute

An attribute whose value is calculated from other attributes. (pg 119)

Determinant

An attribute on which some other attribute is fully functionally dependent. (pg 72)

Determination

The state in which knowing the value of one attribute makes it possible to determine the value of another. (pg 72)

Entity

A person, place, thing, or event about which data will be collected and stored. An entity represents a particular type of object in the real world, which means an entity is 'distinguishable'—that is, each entity occurrence is unique and distinct (pg 36)

Entity Instance

A single occurrence of an entity, also known as a row or a record. (pg 36)

Entity Integrity

A condition in which each row in a table has a unique, non-null primary key. (pg 74)

Entity Occurrence

Another term for an entity instance.

Entity Relationship (ER) Model

A data model that describes the structure of a database using entities, attributes, and relationships in a graphical manner. (pg 44)

Entity Relationship Diagram (ERD)

A graphical representation of an ER model. (pg 44)

Existence-Dependent

An entity that cannot exist without another entity. (pg 122)

Existence-Independent

An entity that can exist without relying on another entity. (pg 122)

Flags

Special codes Indicators used to indicate the absence of some value. (pg 77)

Foreign Key (FK)

An attribute in one table that is a primary key in another table, used to establish a relationship between the two tables. (pg 74)

Full Functional Dependence

A condition in which an attribute is functionally dependent on a composite key but not on any subset of the key. (pg 73)

Functional Dependence

A relationship in which one or more attributes uniquely determine another attribute. (pg 73)

Homonyms

Attributes that have the same name but different meanings. (pg 88)

Identifiers

One or more attributes that uniquely identify each entity instance. (pg 115)

Index

A data structure that improves the speed of data retrieval operations on a table.

Index Key

An attribute or set of attributes used to create an index.

Iterative Process

A process that repeats a series of steps until a desired outcome is achieved.

Key

An attribute or set of attributes that uniquely identifies a row in a table.

Key Attribute

An attribute that is part of a key.

Mandatory Participation

One entity occurrence requires a corresponding entity occurrence in a particular relationship.

Many-to-Many (M:N or ..) Relationship

A relationship in which many instances of one entity are associated with many instances of another entity. Cannot be implemented in an RDBMS.

Multivalued Attributes

Attributes that can have multiple values for a single entity instance.

Optional Attribute

An attribute that does not require a value; therefore, it can be left empty.

Optional Participation

A condition in which an entity may or may not participate in a relationship.

Participants

Entities that take part in a relationship.

Primary Key (PK)

An attribute or set of attributes that uniquely identifies each row in a table.

Recursive Relationship

A relationship between different instances of the same entity.

Referential Integrity

A condition in which every foreign key value matches a primary key value.

Regular Entity

Another term for a strong entity.

Relation

A two-dimensional structure composed of intersecting rows and columns. Another term for a table in a relational database.

Relational Diagram

A graphical representation of a relational database's entities, attributes, and relationships.

Relational Model

A data model based on the theory of relations, which uses tables to represent data and relationships.

Relational Schema

The structure of a relational database, including tables, columns, and relationships.

Relationship

An association between entities.

Relationship Degree

The number of entities involved in a relationship.

Required Attribute

An attribute that must have a value.

Schema

The overall structure of a database.

Secondary Key

An attribute used for data retrieval purposes, but not necessarily unique.

Simple Attribute

An attribute that cannot be subdivided.

Single-Valued Attribute

An attribute that can have only one value for a single entity instance.

Strong (Identifying) Relationship

A relationship in which the child entity is existence-dependent on the parent entity because the primary key of the entity contains a primary key component of the parent entity.

Strong Entity

An entity that is existence-independent, meaning it is not dependent on another entity for its identification.

Superkey

An attribute or set of attributes that uniquely identifies each row in a table.

System Catalog

A repository of metadata about the database. A detailed system data dictionary that describes all objects within the database, including data about table names, table's creator and creation date, number of columns in each table, data type corresponding to each column, index filenames, index creators, authorized users, and access privileges.

Table

A two-dimensional structure composed of intersecting rows and columns. Another term for a relation in a relational database.

Ternary Relationship

A relationship involving three entities.

Tuple

Another term for a row in a table.

Unary Relationship

A relationship between instances of the same entity.

Unique Index

An index that ensures all values in the indexed column are unique.

Weak (Non-Identifying) Relationship

A relationship in which the child entity is existence-independent of the parent entity because the primary key of the child entity does not contain a primary key component of the parent entity. Also known as a non-identifying relationship.

Weak Entity

An entity that is existence-dependent on another entity because it cannot exist without the entity with which it has a relationship and has a primary key that is partially or totally derived from the parent entity in the relationship.