A name–value pair, also called an attribute–value pair, key–value pair, or field–value pair, is a fundamental
data representation
Data and information visualization (data viz or info viz) is an interdisciplinary field that deals with the graphic representation of data and information. It is a particularly efficient way of communicating when the data or information is nu ...
in
computing systems and
applications
Application may refer to:
Mathematics and computing
* Application software, computer software designed to help the user to perform specific tasks
** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...
. Designers often desire an open-ended
data structure
In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...
that allows for
future extension without modifying existing code or data. In such situations, all or part of the
data model
A data model is an abstract model that organizes elements of data and standardizes how they relate to one another and to the properties of real-world entities. For instance, a data model may specify that the data element representing a car be co ...
may be expressed as a collection of
2-tuples in the form <
''attribute name'', ''value''> with each element being an attribute–value pair. Depending on the particular application and the implementation chosen by programmers, attribute names may or may not be unique.
Some of the applications where information is represented as attribute–value pairs are:
*
E-mail
Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" meant ...
, in RFC 2822 headers
*
Query string
A query string is a part of a uniform resource locator (URL) that assigns values to specified parameters. A query string commonly includes fields added to a base URL by a Web browser or other client application, for example as part of an HTML, cho ...
s, in
URLs
* Optional elements in
network protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...
s, such as
IP, where they often appear as
TLV (''type–length–value'') triples
* Bibliographic information, as in
BibTeX
BibTeX is reference management software for formatting lists of references. The BibTeX tool is typically used together with the LaTeX document preparation system. Within the typesetting system, its name is styled as . The name is a portmanteau ...
and
Dublin Core
220px, Logo image of DCMI, which formulates Dublin Core
The Dublin Core, also known as the Dublin Core Metadata Element Set (DCMES), is a set of fifteen "core" elements (properties) for describing resources. This fifteen-element Dublin Core has ...
metadata
* Element attributes in
SGML,
HTML
The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...
, and
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable ...
private
metadata
Metadata is "data that provides information about other data", but not the content of the data, such as the text of a message or the image itself. There are many distinct types of metadata, including:
* Descriptive metadata – the descriptive ...
in
RDF
* Some kinds of
database
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases sp ...
systems – namely a
key–value database
A key–value database, or key–value store, is a data storage paradigm designed for storing, retrieving, and managing associative arrays, and a data structure more commonly known today as a ''dictionary'' or ''hash table''. Dictionaries conta ...
* private map map data
*
Windows registry
The Windows Registry is a hierarchical database that stores low-level settings for the Microsoft Windows operating system and for applications that opt to use the registry. The kernel, device drivers, services, Security Accounts Manager, and use ...
entries
*
Environment variables
An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP envi ...
Some
computer language
A computer language is a formal language used to communicate with a computer. Types of computer languages include:
* Construction language – all forms of communication by which a human can specify an executable problem solution to a compu ...
s implement attribute–value pairs, or more frequently collections of attribute–value pairs, as standard language features. Most of these implement the general model of an
associative array
In computer science, an associative array, map, symbol table, or dictionary is an abstract data type that stores a collection of (key, value) pairs, such that each possible key appears at most once in the collection. In mathematical terms an ...
: an unordered list of unique attributes with associated values. As a result, they are not fully general; they cannot be used, for example, to implement electronic mail headers (which are ordered and non-unique).
In some applications, an attribute–value pair has a value that contains a
nested collection of attribute–value pairs. Some
data private formats such as
JSON
JSON (JavaScript Object Notation, pronounced ; also ) is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of attribute–value pairs and arrays (or other ser ...
support arbitrarily deep nesting.
Other data representations are restricted to one level of nesting, such as
INI file's section/name/value.
See also
*
Attribute (computing)
In computing, an attribute is a specification that defines a property of an object, element, or file. It may also refer to or set the specific value for a given instance of such. For clarity, attributes should more correctly be considered meta ...
*
Entity–attribute–value model
Entity–attribute–value model (EAV) is a data model to encode, in a space-efficient manner, entities where the number of attributes (properties, parameters) that can be used to describe them is potentially vast, but the number that will actuall ...
*
Query string
A query string is a part of a uniform resource locator (URL) that assigns values to specified parameters. A query string commonly includes fields added to a base URL by a Web browser or other client application, for example as part of an HTML, cho ...
*
Key–value database
A key–value database, or key–value store, is a data storage paradigm designed for storing, retrieving, and managing associative arrays, and a data structure more commonly known today as a ''dictionary'' or ''hash table''. Dictionaries conta ...
References
{{DEFAULTSORT:Attribute-Value Pair
Data modeling