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.

Because the relational model emphasizes search rather than navigation, it does not make relationships between different entities explicit in the form of pointers, but represents them rather using primary keys and foreign keys.

The rigidity of the relational model, in which all data is held in tables with a fixed structure of rows and columns, has increasingly been seen as a limitation when handling information that is richer or more varied in structure than the traditional ' ledger-book ' data of corporate information systems: for example, document databases, engineering databases, multimedia databases, or databases used in the molecular sciences.

The relational model is a simple model that provides flexibility.

The most common language associated with the relational model is the Structured Query Language ( SQL ), though it differs in some places.

Products offering a more general data model than the relational model are sometimes classified as post-relational.

Some of these extensions to the relational model integrate concepts from technologies that pre-date the relational model.

A major Relational model language supported by all the relational DBMSs and a standard.

SQL was one of the first commercial languages for the relational model.

Despite not adhering to the relational model as described by Codd, it has become the most widely used database language.

Clearly separating the three levels was a major feature of the relational database model implementations that dominate 21st century databases.

In practice usually a given DBMS uses the same data model for both the external and the conceptual levels ( e. g., relational model ).

DBMSs can be categorized according to the database model ( s ) that they support, such as relational or XML, the type ( s ) of computer they support, such as a server cluster or a mobile phone, the query language ( s ) that access the database, such as SQL or XQuery, performance trade-offs, such as maximum scale or maximum speed or others.

DBMSs may use a variety of database models, such as the relational model or object model, to conveniently describe and support applications.

The relational model solved this by splitting the data into a series of normalized tables ( or relations ), with optional elements being moved out of the main table to where they would take up room only if needed.

In the relational model, related records are linked together with a " key "

In the relational model, some bit of information was used as a " key ", uniquely defining a particular record.

IBM itself did one test implementation of the relational model, PRTV, and a production one, Business System 12, both now discontinued.

Alternatively, and especially in connection with the relational model of database management, the relation between attributes drawn from a specified set of domains can be seen as being primary.

The fundamental assumption of the relational model is that all data is represented as mathematical n-ary relations, an n-ary relation being a subset of the Cartesian product of n domains.

In accordance with this Principle, a relational database is a set of relvars and the result of every query is presented as a relation.

To fully appreciate the relational model of data it is essential to understand the intended interpretation of a relation.

The relational model requires there to be no significance to any ordering of the attributes of a relation.

The relational model depends on the law of excluded middle under which anything that is not true is false and anything that is not false is true ; it also requires every tuple in a relation body to have a value for every attribute of that relation.

Basic notions in the relational model are relation names and attribute names.

The next definition defines relation which formalizes the contents of a table as it is defined in the relational model.

Usually in the relational model a database schema is said to consist of a set of relation names, the headers that are associated with these names and the constraints that should hold for every instance of the database schema.

It is usually written in the form of a pair of expressions denoting the values in question, with a relational sign between them indicating the specific inequality relation.

In the relational model, a relation is a ( possibly empty ) finite set of tuples all having the same finite set of attributes.

We define headers as finite subsets of C. A relational database schema is defined as a tuple S = ( D, R, h ) where D is the domain of atomic values ( see relational model for more on the notions of domain and atomic value ), R is a finite set of relation names, and

a function that associates a header with each relation name in R. ( Note that this is a simplification from the full relational model where there is more than one domain and a header is not just a set of column names but also maps these column names to a domain.

First normal form ( 1NF ) is a property of a relation in a relational database.

First normal form is an essential property of a relation in a relational database.

This usually embodies the relational ( as opposed to functional ) view of a rule of inference, where the turnstile stands for a deducibility relation holding between premises and conclusion.

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

* the unary operation of selection on a database relation in relational algebra

This corresponds to a single relation in a relational database, or to data ( though not calculations ) in a typical spreadsheet.

In a relational database, similar issues are readily handled by creating a separate relation for each such group, and connecting " child " records to the related " parent " records using a foreign key ( such as an ID number or name for the parent ).

The adjective expresses three main ideas: quality ( qualitative adjectives, kakovostni pridevniki ), relation ( relational adjectives, vrstni pridevniki ) and possession ( possessive adjectives, svojilni pridevniki ).

— Introduction to Tarskian relation theory and its applications within the relational programming paradigm.

Berkeley DB is not a relational database.

A normal relational database however, is not efficient for business intelligence reports where dimensional modelling is prevalent.

Results from an experiment by Davachi, Mitchell, and Wagner ( 2003 ) and numerous subsequent studies ( Davachi, 2006 ) show that activation in the hippocampus during encoding is related to a subject's ability to recall prior events or later relational memories.

In the design of a relational database, the process of organizing database relations to minimize redundancy is called normalization.

In a relational database clustering the two respective relations " Items " and " Orders " results in saving the expensive execution of a Join operation between the two relations whenever such a join is needed in a query ( the join result is already ready in storage by the clustering, available to be utilized ).

Further, there is no reason that relational normalization concepts cannot be applied to CODASYL databases however, in the final tally, CODASYL was very complex and required significant training and effort to produce useful applications.

The relational structure is the most commonly used today.

The multidimensional structure is similar to the relational model.

The dominant model in use today is the ad hoc one embedded in SQL, despite the objections of purists who believe this model is a corruption of the relational model since it violates several fundamental principles for the sake of practicality and performance.

A relational normalised database imposes a heavy access load over physical storage of data even if it is well tuned for high performance.

Database normalization is the process of organizing the fields and tables of a relational database to minimize redundancy and dependency.

Informally, a relational database table is often described as " normalized " if it is in the Third Normal Form.

Settlement geography, including urban geography, is the study of urban and rural areas with specific regards to spatial, relational and theoretical aspects of settlement.

A key field is a field or set of fields ( a key is then said to be a composite key ) of a database ( typically a relational database ) table which together form a unique identifier for a database record ( a table entry ).

WordNet " is a type of an online electronic lexical database organized on relational principles, which now comprises nearly 100, 000 concepts " as Dirk Geeraerts states it.

There are attempts to introduce a category of relational disorder, where the diagnosis is of a relationship rather than on any one individual in that relationship.