Relational Database Fundamentals

thin client

A client designed to be small so that the bulk of the data processing occurs on the server.

fat client

A client that performs the bulk of the data-processing operations.

foreign key

A column or concatenated columns that are identical to the primary key of a relation in the same database.

entity-relationship (ER) modeling

A conceptual database design method that describes relationships between entities.

view

A data operation given a name and stored in a database that creates virtual tables when invoked by a user.

null

A database value meaning "unknown."

Data Definition Language (DDL)

A descriptive language used to create and name entities and the relationships between them in a database.

data model

A formal method of describing data and data relationships.

Data Manipulation Language (DML)

A language that provides the interface necessary to perform data operations on data within a database.

Data Control Language (DCL)

A language used to control access to data in a database.

composite key

A primary or foreign key that is made up of multiple attributes.

column (attritubte)

A property of a relation.

referential integrity

A relational constraint stating that every foreign key that is not null must reference an existing primary key value.

entity integrity

A relational constraint stating that no part of a primary key may be null.

domain constraints

A set of restrictions on the values allowed for the attributes of relations.

data dictionary

A set of tables created as a result of DDL operations that hold metadata about a database.

relation

A two-dimensional table consisting of columns and rows in a relational database.

primary key

A unique identifier within a row.

entity

A uniquely identifiable element about which data is stored in a database.

weak entity

An entity that must reference another entity for its data to be meaningful.

strong entity

An entity whose data is meaningful without having to reference another entity in the data model.

virtual tables

Database relations created as a result of a data manipulation operation and not a permanent part of the database.

row (tuple)

The collection of one set of attributes in a relation.

degree

The number of attributes in a relation.

cardinality

The number of rows in a relation.

query language

The part of nonprocedural DML that retrieves data from a database.

parent key

The primary key referenced by a foreign key.

normalization

The process of organizing and refining relations within a relational database.

base tables

The relations actually defined within a database.

domain

the allowable values for an attribute.