Relational model

relationalrelational data modelrelationshipsrelational databaserelational datarelational model of dataRelationship relationaldatabase keymodeling the relational patterns
The relational model (RM) for database management is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations.wikipedia
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Edgar F. Codd

E. F. CoddCoddE.F. Codd
The relational model (RM) for database management is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations. There have been several attempts to produce a true implementation of the relational database model as originally defined by Codd and explained by Date, Darwen and others, but none have been popular successes so far.
Edgar Frank "Ted" Codd (19 August 1923 – 18 April 2003) was an English computer scientist who, while working for IBM, invented the relational model for database management, the theoretical basis for relational databases and relational database management systems.

Relational database

relational databasesrelationaldatabase constraints
A database organized in terms of the relational model is a relational database.
A relational database is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970.

SQL

Structured Query LanguageSQL DatabasesWikibook SQL
Most relational databases use the SQL data definition and query language; these systems implement what can be regarded as an engineering approximation to the relational model.
SQL was one of the first commercial languages for Edgar F. Codd's relational model.

Hugh Darwen

Darwen
There have been several attempts to produce a true implementation of the relational database model as originally defined by Codd and explained by Date, Darwen and others, but none have been popular successes so far.
Hugh Darwen is a computer scientist who was an employee of IBM United Kingdom from 1967 to 2004, and has been involved in the history of the relational model.

Null (SQL)

NULL NULLs
Codd himself, some years after publication of his 1970 model, proposed a three-valued logic (True, False, Missing/NULL) version of it to deal with missing information, and in his The Relational Model for Database Management Version 2 (1990) he went a step further with a four-valued logic (True, False, Missing but Applicable, Missing but Inapplicable) version.
Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfil the requirement that all true relational database management systems (RDBMS) support a representation of "missing information and inapplicable information".

Structure (mathematical logic)

structuremodelstructures
The content of the database at any given time is a finite (logical) model of the database, i.e. a set of relations, one per predicate variable, such that all predicates are satisfied.
In database theory, structures with no functions are studied as models for relational databases, in the form of relational models.

Rel (DBMS)

Rel
Rel is one of the more recent attempts to do this.
Rel is an open-source true relational database management system that implements a significant portion of Chris Date and Hugh Darwen's Tutorial D query language.

Network model

networknetwork data modelnetwork database
Other models are the hierarchical model and network model.
Secondly, it was eventually displaced by the relational model, which offered a higher-level, more declarative interface.

Hierarchical database model

hierarchical databasehierarchical modelhierarchical
Other models are the hierarchical model and network model.
The hierarchical data model lost traction as Codd's relational model became the de facto standard used by virtually all mainstream database management systems.

Relational algebra

joinrelational logicθ''-join
Data are operated upon by means of a relational calculus or relational algebra, these being equivalent in expressive power.
Relational algebra received little attention outside of pure mathematics until the publication of E.F. Codd's relational model of data in 1970.

The Third Manifesto

In The Third Manifesto (first published in 1995) Date and Darwen attempt to show how the relational model can allegedly accommodate certain "desired" object-oriented features.
The Third Manifesto proposes to maintain the relational model for databases and to support objects as user-defined types.

Database normalization

normalizationnormalizednormal form
The theory includes a process of database normalization whereby a design with certain desirable properties can be selected from a set of logically equivalent alternatives.
It was first proposed by Edgar F. Codd as an integral part of his relational model.

Candidate key

candidatecandidate keyskey candidates
In practice, several useful shorthands are expected to be available, of which the most important are candidate key (really, superkey) and foreign key constraints. Usually one candidate key is chosen to be called the primary key and used in preference over the other candidate keys, which are then called alternate keys.
In the relational model of databases, a candidate key of a relation is a minimal superkey for that relation; that is, a set of attributes such that:

Christopher J. Date

Chris DateC.J. DateChristopher J Date
There have been several attempts to produce a true implementation of the relational database model as originally defined by Codd and explained by Date, Darwen and others, but none have been popular successes so far.
He was also involved with Edgar F. Codd’s relational model for database management.

Superkey

In practice, several useful shorthands are expected to be available, of which the most important are candidate key (really, superkey) and foreign key constraints.
A superkey or super-key is defined in the relational model of database organization as a set of attributes of a relation variable for which it holds that in all relations assigned to that variable, there are no two distinct tuples (rows) that have the same values for the attributes in this set.

Database

database management systemdatabasesdatabase systems
The relational model (RM) for database management is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations. The access plans and other implementation and operation details are handled by the DBMS engine, and are not reflected in the logical model.
The relational model, first proposed in 1970 by Edgar F. Codd, departed from this tradition by insisting that applications should search for data by content, rather than by following links.

Query plan

access planexecutionexecution path
The access plans and other implementation and operation details are handled by the DBMS engine, and are not reflected in the logical model.
This is a specific case of the relational model concept of access plans.

Relational calculus

Data are operated upon by means of a relational calculus or relational algebra, these being equivalent in expressive power.
Relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries.

Primary key

alternate keydefining database keykey
Usually one candidate key is chosen to be called the primary key and used in preference over the other candidate keys, which are then called alternate keys.
In the relational model of databases, a primary key is a specific choice of a minimal set of attributes (columns) that uniquely specify a tuple (row) in a relation (table).

Object database

object-oriented databaseobject-oriented databasesobject-oriented
Also of note are newer object-oriented databases.
Relational model

Table (database)

tabletablesdatabase table
A table is an accepted visual representation of a relation; a tuple is similar to the concept of a row.
In terms of the relational model of databases, a table can be considered a convenient representation of a relation, but the two are not strictly equivalent.

Relvar

Base relvarrelation variablerelvars
A relvar is a named variable of some specific relation type, to which at all times some relation of that type is assigned, though the relation may contain zero tuples.
In relational databases, relvar is a term introduced by C. J. Date and Hugh Darwen as an abbreviation for relation variable in their 1995 paper The Third Manifesto, to avoid the confusion sometimes arising from the use of the term relation, by the inventor of the relational model, E. F. Codd, for a variable to which a relation is assigned as well as for the relation itself.

First-order logic

predicate logicfirst-orderpredicate calculus
The relational model (RM) for database management is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations.
Relational model

Database design

Database Constructiondatabase structuredatabase system architecture
There is a flaw in our database design above.
(NOTE: A common misconception is that the relational model is so called because of the stating of relationships between data elements therein.

Relational database management system

RDBMSrelational database management systemsrelational database
Relational database management system
A relational database management system (RDBMS) is a database management system (DBMS) based on the relational model of data.