alternate key
all candidate keys not chosen as the primary key
Alternate keys are all candidate keys not chosen as the primary key.
candidate key
a simple or composite key that is unique (no two rows in a table may have the same value) and minimal (every column is necessary)
A candidate key is a simple or composite key that is unique and minimal.
characteristic entities
entities that provide more information about another table
You should also be familiar with different kinds of entities including independent entities, dependent entities and characteristic entities.
composite attributes
attributes that consist of a hierarchy of attributes
Composite attributes are those that consist of a hierarchy of attributes.
composite key
composed of two or more attributes, but it must be minimal
A candidate key is a simple or composite key that is unique and minimal.
dependent entities
these entities depend on other tables for their meaning
You should also be familiar with different kinds of entities including independent entities, dependent entities and characteristic entities.
derived attributes
attributes that contain values calculated from other attributes
Derived attributes are attributes that contain values calculated from other attributes.
derived entities
see dependent entities
Dependent entities, also referred to as derived entities, depend on other tables for their meaning.
EID
employee identification (ID)
Employee (EID, Name, Address, Age, Salary) – EID is the simple primary key.
entity
a thing or object in the real world with an independent existence that can be differentiated from other objects
An entity is an object in the real world with an independent existence that can be differentiated from other objects.
entity relationship (ER) data model
also called an ER schema, are represented by ER diagrams. These are well suited to data modelling for use with databases.
The entity relationship (ER) data model has existed for over 35 years.
entity relationship schema
see entity relationship data model
ER models, also called an ER schema, are represented by ER diagrams.
entity set
a collection of entities of an entity type at a point of time
An entity set is a collection of entities of an entity type at a particular point of time.
entity type
a collection of similar entities
Another term to know is entity type which defines a collection of similar entities.
foreign key (FK)
an attribute in a table that references the primary key in another table OR it can be null
It is existence-dependent if it has a mandatory foreign key (i.e., a foreign key attribute that cannot be null).
independent entity
as the building blocks of a database, these entities are what other tables are based on
If we refer back to our COMPANY database, examples of an independent entity include the Customer table, Employee table or Product table.
kernel
see independent entity
Independent entities, also referred to as kernels, are the backbone of the database.
key
an attribute or group of attributes whose values can be used to uniquely identify an individual entity in an entity set
The Spouse table, in the COMPANY database, is a weak entity because its primary key is dependent on the Employee table.
multivalued attributes
attributes that have a set of values for each entity
Multivalued attributes are attributes that have a set of values for each entity.
n-ary
multiple tables in a relationship
Note n-ary means multiple tables in a relationship.
null
a special symbol, independent of data type, which means either unknown or inapplicable; it does not mean zero or blank
It is existence-dependent if it has a mandatory foreign key (i.e., a foreign key attribute that cannot be null).
recursive relationship
see unary relationship
A unary relationship, also called recursive, is one in which a relationship exists between occurrences of the same entity set.
relationships
the associations or interactions between entities; used to connect related information between tables
Many to many relationships become associative tables with at least two foreign keys.
relationship strength
based on how the primary key of a related entity is defined
Relationship strength is based on how the primary key of a related entity is defined.
secondary key
an attribute used strictly for retrieval purposes
A secondary key is an attribute used strictly for retrieval purposes (can be composite), for example: Phone and Last Name.
simple attributes
drawn from the atomic value domains
Simple attributes are those drawn from the atomic value domains.
SIN
social insurance number
In the Employee table, both EID and SIN are possible candidate keys.
single-valued attributes
see simple attributes
Simple attributes are also called single-valued attributes.
stored attribute
saved physically to the database
In this situation, Birthdate is called a stored attribute, which is physically saved to the database.
ternary relationship
a relationship type that involves many to many relationships between three tables.
A ternary relationship is a relationship type that involves many to many relationships between three tables.
unary relationship
one in which a relationship exists between occurrences of the same entity set.
A unary relationship, also called recursive, is one in which a relationship exists between occurrences of the same entity set.
These terms were extracted from Database Design – 2nd Edition by Adrienne Watt, eCampusOntario (originally published by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License. Chapter text adapted from Data Modeling Using Entity-Relationship Model by Nguyen Kim Anh, licensed under CC BY 3.0.