Databases

Attribute

A part of a tuple or a value; in Entity/Relationship modeling a property of an entity or relationship. An attribute has a name and takes values from some domain

Entity Integrity

Attributes of the primary key can not be Null

Prime Attribute

An attribute in relation R is a part of a key of R

Column

Part of a row that holds a value from some domain; in a relational database it is a synonym for field.

Table

A collection of data organized in rows and columns. In database terminology a synonym for relation.

Table Instance

A collection of rows that are the current contents of a table. The table instance changes whenever rows are inserted, deleted or modified

Referential Integrity

A foreign key value is either Null or its value appears in the referenced table

Third Normal Form

A relation, R, is in 3NF if for every nontrivial functional dependency (X -> A) that lies in R either X is a super key or A is a prime attribute

Constraint

A restriction on the data that can be entered into the database

Tuple

A set of attributes; an ordered tuple is a sequence or list of attributes.

Relation

A set of tuples

Data Type

A set of values and operations that can be performed on the values

Key

A subset of the attributes of a table that has the super key property and does not contain a subset that also has the super key property.

Foreign Key

A subset of the attributes of a table that reference the primary key of a related table

Super Key

A subset of the attributes of a table that uniquely identifies each row in the table. In terms of functional dependencies a subset of the attributes of a table that functional determines all the attributes in the table.

Record

A synonym for row

Entity

A thing or concept about which data will be stored in the database. The data associated with an entity has multiple parts that are referred to as attributes

Relationship

An association among two or more entities

Query

An expression that retrieves data from the database that satisfies certain constraints

Row

An instance of data in a table also known as a record or tuple

Null Type

An unknown value

Metadata

Data about the data in the database such at the names of the tables.

Table Definition

Defines the structure of a table including the columns that are part of each row and the data types of the columns. The structure is determined when the database is designed.

Functional Dependency

Given a set of attributes X and an attribute A, X functionally determines A (written X -> A) if and only if for a given value of X there is at most one value for A

Primary Key

One of the keys of a table

SQL

The standard relational database language; it can be used to specify the structure of the database and to query the database.