![Web 2](https://upload.wikimedia.org/wikipedia/commons/a/a7/Web_2.0_Map.svg)
In
information system
An information system (IS) is a formal, sociotechnical, organizational system designed to collect, process, store, and distribute information. From a sociotechnical perspective, information systems are composed by four components: task, people ...
s, a tag is a
keyword or term assigned to a piece of information (such as an
Internet bookmark
In the context of the World Wide Web, a bookmark is a Uniform Resource Identifier (URI) that is stored for later retrieval in any of various storage formats. All modern web browsers include bookmark features. Bookmarks are called favorites or I ...
,
multimedia
Multimedia is a form of communication that uses a combination of different content forms such as text, audio, images, animations, or video into a single interactive presentation, in contrast to tradit ...
, database
record, or
computer file
A computer file is a computer resource for recording data in a computer storage device, primarily identified by its file name. Just as words can be written to paper, so can data be written to a computer file. Files can be shared with and trans ...
). This kind of
metadata helps describe an item and allows it to be found again by browsing or searching. Tags are generally chosen informally and personally by the item's creator or by its viewer, depending on the system, although they may also be chosen from a
controlled vocabulary
Control may refer to:
Basic meanings Economics and business
* Control (management), an element of management
* Control, an element of management accounting
* Comptroller (or controller), a senior financial officer in an organization
* Controllin ...
.
Tagging was popularized by
website
A website (also written as a web site) is a collection of web pages and related content that is identified by a common domain name and published on at least one web server. Examples of notable websites are Google, Facebook, Amazon, and Wi ...
s associated with
Web 2.0
Web 2.0 (also known as participative (or participatory) web and social web) refers to websites that emphasize user-generated content, ease of use, participatory culture and interoperability (i.e., compatibility with other products, systems, and ...
and is an important feature of many Web 2.0 services.
It is now also part of other
database system
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 spa ...
s,
desktop application
A desktop traditionally refers to:
* The surface of a desk (often to distinguish office appliances that fit on a desk, such as photocopiers and printers, from larger equipment covering its own area on the floor)
Desktop may refer to various compu ...
s, and
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...
s.
Overview
People use tags to aid
classification, mark ownership, note
boundaries, and indicate
online identity
Internet identity (IID), also online identity or internet persona, is a social identity that an Internet user establishes in online communities and websites. It may also be an actively constructed presentation of oneself. Although some people choo ...
. Tags may take the form of words, images, or other identifying marks. An analogous example of tags in the physical world is
museum
A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make thes ...
object tagging. People were using textual
keyword
Keyword may refer to:
Computing
* Keyword (Internet search), a word or phrase typically used by bloggers or online content creator to rank a web page on a particular topic
* Index term, a term used as a keyword to documents in an information syst ...
s to
classify information and objects long before computers. Computer based
search algorithm
In computer science, a search algorithm is an algorithm designed to solve a search problem. Search algorithms work to retrieve information stored within particular data structure, or calculated in the search space of a problem domain, with eith ...
s made the use of such keywords a rapid way of exploring records.
Tagging gained popularity due to the growth of
social bookmarking
Social bookmarking is an online service which allows users to add, annotate, edit, and share bookmarks of web documents. Many online bookmark management services have launched since 1996; Delicious, founded in 2003, popularized the terms "social ...
,
image sharing
Image sharing, or photo sharing, is the publishing or transfer of digital photos online. Image sharing websites offer services such as uploading, hosting, managing and sharing of photos (publicly or privately). This function is provided through ...
, and
social networking websites.
These sites allow users to create and manage labels (or "tags") that categorize content using simple keywords. Websites that include tags often display collections of tags as
tag cloud
A tag cloud (also known as a word cloud, wordle or weighted list in visual design) is a visual representation of text data, which is often used to depict keyword metadata on websites, or to visualize free form text. Tags are usually single word ...
s,
[For example, ]Blogger
A blog (a truncation of "weblog") is a discussion or informational website published on the World Wide Web consisting of discrete, often informal diary-style text entries (posts). Posts are typically displayed in reverse chronological order ...
and WordPress
WordPress (WP or WordPress.org) is a free and open-source content management system (CMS) written in hypertext preprocessor language and paired with a MySQL or MariaDB database with supported HTTPS. Features include a plugin architecture ...
can display tag clouds. as do some desktop applications.
[For example: Leap is a ]macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
application that features a clickable tag cloud of macOS tags: TaggTool is a Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ser ...
application that permits tagging files and displaying a tag cloud: On websites that aggregate the tags of all users, an individual user's tags can be useful both to them and to the larger community of the website's users.
Tagging systems have sometimes been classified into two kinds: ''top-down'' and ''bottom-up''.
Top-down
taxonomies are created by an authorized group of designers (sometimes in the form of a
controlled vocabulary
Control may refer to:
Basic meanings Economics and business
* Control (management), an element of management
* Control, an element of management accounting
* Comptroller (or controller), a senior financial officer in an organization
* Controllin ...
), whereas bottom-up taxonomies (called
folksonomies) are created by all users.
This definition of "top down" and "bottom up" should not be confused with the distinction between a ''single hierarchical''
tree structure
A tree structure, tree diagram, or tree model is a way of representing the hierarchical nature of a structure in a graphical form. It is named a "tree structure" because the classic representation resembles a tree, although the chart is genera ...
(in which there is one correct way to classify each item) versus ''multiple non-hierarchical''
sets (in which there are multiple ways to classify an item); the structure of both top-down and bottom-up taxonomies may be either hierarchical, non-hierarchical, or a combination of both.
Some researchers and applications have experimented with combining hierarchical and non-hierarchical tagging to aid in information retrieval. Others are combining top-down and bottom-up tagging, including in some large library catalogs (
OPAC
The online public access catalog (OPAC), now frequently synonymous with ''library catalog'', is an online database of materials held by a library or group of libraries. Online catalogs have largely replaced the analog card catalogs previously ...
s) such as
WorldCat
WorldCat is a union catalog that itemizes the collections of tens of thousands of institutions (mostly libraries), in many countries, that are current or past members of the OCLC global cooperative. It is operated by OCLC, Inc. Many of the O ...
.
When tags or other taxonomies have further properties (or
semantics
Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comp ...
) such as
relationships and
attribute
Attribute may refer to:
* Attribute (philosophy), an extrinsic property of an object
* Attribute (research), a characteristic of an object
* Grammatical modifier, in natural languages
* Attribute (computing), a specification that defines a prope ...
s, they constitute an
ontology
In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality.
Ontology addresses questions like how entities are grouped into categories and which of these entities exi ...
.
Metadata tags as described in this article should not be confused with the use of the word "tag" in some software to refer to an automatically generated
cross-reference; examples of the latter are ''tags tables'' in
Emacs and
''smart tags'' in
Microsoft Office
Microsoft Office, or simply Office, is the former name of a family of client software, server software, and services developed by Microsoft. It was first announced by Bill Gates on August 1, 1988, at COMDEX in Las Vegas. Initially a marketi ...
.
History
The use of keywords as part of an identification and classification system long predates computers.
Paper data storage
Paper data storage refers to the use of paper as a data storage device. This includes writing, illustrating, and the use of data that can be interpreted by a machine or is the result of the functioning of a machine. A defining feature of paper d ...
devices, notably
edge-notched card
Edge-notched cards or edge-punched cards are a system used to store a small amount of binary or logical data on paper index cards, encoded via the presence or absence of notches in the edges of the cards. The notches allowed efficient sorting and s ...
s, that permitted classification and sorting by multiple criteria were already in use prior to the twentieth century, and
faceted classification
A faceted classification is a classification scheme used in organizing knowledge into a systematic order. A faceted classification uses semantic categories, either general or subject-specific, that are combined to create the full classification ent ...
has been used by libraries since the 1930s.
In the late 1970s and early 1980s, the
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
text editor
A text editor is a type of computer program that edits plain text. Such programs are sometimes known as "notepad" software (e.g. Windows Notepad). Text editors are provided with operating systems and software development packages, and can be ...
Emacs offered a companion software program called ''Tags'' that could automatically build a table of cross-references called a ''tags table'' that Emacs could use to jump between a
function call
In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed.
Functions may ...
and that function's definition. This use of the word "tag" did not refer to metadata tags, but was an early use of the word "tag" in software to refer to a
word index.
Online databases and early websites deployed keyword tags as a way for publishers to help users find content. In the early days of the
World Wide Web
The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet.
Documents and downloadable media are made available to the network through web ...
, the
keywords
meta element
Meta elements are tags used in HTML and XHTML documents to provide structured metadata about a Web page.
They are part of a web page's head section. Multiple Meta elements with different attributes can be used on the same page. Meta elements can ...
was used by
web designer
Web design encompasses many different skills and disciplines in the production and maintenance of websites. The different areas of web design include web graphic design; user interface design (UI design); authoring, including standardised code a ...
s to tell
web search engine
A search engine is a software system designed to carry out web searches. They search the World Wide Web in a systematic way for particular information specified in a textual web search query. The search results are generally presented in a ...
s what the web page was about, but these keywords were only visible in a web page's
source code
In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the w ...
and were not modifiable by users.
![A Description of the Equator and Some Otherlands, collaborative hypercinema portal Upload page](https://upload.wikimedia.org/wikipedia/commons/e/eb/A_Description_of_the_Equator_and_Some_Otherlands%2C_collaborative_hypercinema_portal_Upload_page.jpg)
In 1997, the collaborative portal "A Description of the Equator and Some ØtherLands" produced by
documenta X, Germany, used the
folksonomic term ''Tag'' for its co-authors and guest authors on its Upload page. In "The Equator" the term ''Tag'' for user-input was described as an ''abstract literal or keyword'' to aid the user. However, users defined singular ''Tags'', and did not share ''Tags'' at that point.
In 2003, the
social bookmarking
Social bookmarking is an online service which allows users to add, annotate, edit, and share bookmarks of web documents. Many online bookmark management services have launched since 1996; Delicious, founded in 2003, popularized the terms "social ...
website
Delicious provided a way for its users to add "tags" to their bookmarks (as a way to help find them later);
Delicious also provided browseable aggregated views of the bookmarks of all users featuring a particular tag. Within a couple of years, the
photo sharing
Image sharing, or photo sharing, is the publishing or transfer of digital photos online. Image sharing websites offer services such as uploading, hosting, managing and sharing of photos (publicly or privately). This function is provided through ...
website
Flickr
Flickr ( ; ) is an American image hosting and video hosting service, as well as an online community, founded in Canada and headquartered in the United States. It was created by Ludicorp in 2004 and was a popular way for amateur and profession ...
allowed its users to add their own text tags to each of their pictures, constructing flexible and easy metadata that made the pictures highly searchable. The success of Flickr and the influence of Delicious popularized the concept, and other
social software
Social software, also known as social apps or social platform, include communications and interactive tools that are often based on the Internet. Communication tools typically handle the capturing, storing and presentation of communication, usua ...
websites—such as
YouTube
YouTube is a global online video sharing and social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by Google, and is the second mo ...
,
Technorati
Technorati was a search engine and a publisher advertising platform that served as an advertising solution for the thousands of websites in its network. Technorati launched its ad network in 2008, and at one time was one of the largest ad network ...
, and
Last.fm
Last.fm is a music website founded in the United Kingdom in 2002. Using a music recommender system called "Audioscrobbler", Last.fm builds a detailed profile of each user's musical taste by recording details of the tracks the user listens to, e ...
—also implemented tagging. In 2005, the
Atom
Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons.
Every solid, liquid, gas, ...
web syndication
Web syndication is a form of syndication in which content is made available from one website to other sites. Most commonly, websites are made available to provide either summaries or full renditions of a website's recently added content. The term ...
standard provided a "category" element for inserting subject categories into
web feed
On the World Wide Web, a web feed (or news feed) is a data format used for providing users with frequently updated content. Content distributors ''syndicate'' a web feed, thereby allowing users to ''subscribe'' a channel to it by adding the feed ...
s, and in 2007
Tim Bray
Timothy William Bray (born June 21, 1955) is a Canadian software developer, environmentalist, political activist and one of the co-authors of the original XML specification. He worked for Amazon Web Services from December 2014 until May 2020 w ...
proposed a "tag"
URN
An urn is a vase, often with a cover, with a typically narrowed neck above a rounded body and a footed pedestal. Describing a vessel as an "urn", as opposed to a vase or other terms, generally reflects its use rather than any particular shape or ...
.
Examples
Within a blog
Many systems (and other web
content management systems) allow authors to add free-form tags to a post, along with (or instead of) placing the post into a predetermined category.
For example, a post may display that it has been tagged with
baseball
and
tickets
. Each of those tags is usually a
web link leading to a index page listing all of the posts associated with that tag. The blog may have a sidebar listing all the tags in use on that blog, with each tag leading to an index page. To reclassify a post, an author edits its list of tags. All connections between posts are automatically tracked and updated by the blog software; there is no need to relocate the page within a complex hierarchy of categories.
Within application software
Some
desktop application
A desktop traditionally refers to:
* The surface of a desk (often to distinguish office appliances that fit on a desk, such as photocopiers and printers, from larger equipment covering its own area on the floor)
Desktop may refer to various compu ...
s and
web application
A web application (or web app) is application software that is accessed using a web browser. Web applications are delivered on the World Wide Web to users with an active network connection.
History
In earlier computing models like client-serv ...
s feature their own tagging systems, such as email tagging in
Gmail
Gmail is a free email service provided by Google. As of 2019, it had 1.5 billion active users worldwide. A user typically accesses Gmail in a web browser or the official mobile app. Google also supports the use of email clients via the POP and ...
and
Mozilla Thunderbird
Mozilla Thunderbird is a free and open-source cross-platform email client, personal information manager, news client, RSS and chat client developed by the Mozilla Foundation and operated by subsidiary MZLA Technologies Corporation. The projec ...
,
bookmark tagging in
Firefox
Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...
, audio tagging in
iTunes or
Winamp
Winamp is a media player for Microsoft Windows originally developed by Justin Frankel and Dmitry Boldyrev by their company Nullsoft, which they later sold to AOL in 1999 for $80 million. It was then acquired by Radionomy in 2014. Sinc ...
, and photo tagging in various applications. Some of these applications display collections of tags as
tag cloud
A tag cloud (also known as a word cloud, wordle or weighted list in visual design) is a visual representation of text data, which is often used to depict keyword metadata on websites, or to visualize free form text. Tags are usually single word ...
s.
Assigned to computer files
There are various systems for applying tags to the files in a computer's
file system.
In
Apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
's
Mac System 7
System 7, codenamed "Big Bang", and also known as Mac OS 7, is a graphical user interface-based operating system for Macintosh computers and is part of the classic Mac OS series of operating systems. It was introduced on May 13, 1991, by Apple C ...
, released in 1991, users could assign one of
seven editable colored labels (with editable names such as "Essential", "Hot", and "In Progress") to each file and folder. In later iterations of the Mac operating system ever since
OS X 10.9 was released in 2013, users could assign multiple arbitrary tags as
extended file attributes Extended file attributes are file system features that enable users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem (such as permissions or re ...
to any file or folder, and before that time the
open-source OpenMeta standard provided similar tagging functionality for
Mac OS X
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and la ...
.
Several
semantic file system
Semantic file systems are file systems used for information persistence which structure the data according to their semantics and intent, rather than the location as with current file systems. It allows the data to be addressed by their content (as ...
s that implement tags are available for the
Linux kernel, including
Tagsistant
Tagsistant is a semantic file system for the Linux kernel, written in C and based on FUSE. Unlike traditional file systems that use hierarchies of directories to locate objects, Tagsistant introduces the concept of tags.
Design and difference ...
.
Microsoft Windows allows users to set tags only on
Microsoft Office
Microsoft Office, or simply Office, is the former name of a family of client software, server software, and services developed by Microsoft. It was first announced by Bill Gates on August 1, 1988, at COMDEX in Las Vegas. Initially a marketi ...
documents and some kinds of picture files.
Cross-platform
In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software ...
file tagging standards include
Extensible Metadata Platform (XMP), an
ISO standard
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
for embedding metadata into popular image, video and document file formats, such as
JPEG and
PDF, without breaking their readability by applications that do not support XMP. XMP largely supersedes the earlier
IPTC Information Interchange Model.
Exif
Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies formats for images, sound, and ancillary tags used by digital cameras (including smartphones), scanners and other syste ...
is a standard that specifies the image and audio
file formats used by
digital camera
A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices ...
s, including some metadata tags.
TagSpaces is an open-source cross-platform application for tagging files; it inserts tags into the
filename.
For an event
An ''official tag'' is a keyword adopted by events and conferences for participants to use in their web publications, such as blog entries, photos of the event, and presentation slides. Search engines can then index them to make relevant materials related to the event searchable in a uniform way. In this case, the tag is part of a
controlled vocabulary
Control may refer to:
Basic meanings Economics and business
* Control (management), an element of management
* Control, an element of management accounting
* Comptroller (or controller), a senior financial officer in an organization
* Controllin ...
.
In research
A researcher may work with a large collection of items (e.g. press quotes, a bibliography, images) in digital form. If he/she wishes to associate each with a small number of themes (e.g. to chapters of a book, or to sub-themes of the overall subject), then a group of tags for these themes can be attached to each of the items in the larger collection. In this way, freeform
classification allows the author to manage what would otherwise be unwieldy amounts of information.
Special types
Triple tags
A triple tag or machine tag uses a special
syntax to define extra
semantic information about the tag, making it easier or more meaningful for interpretation by a computer program. Triple tags comprise three parts: a
namespace
In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified.
Namespaces ...
, a
predicate
Predicate or predication may refer to:
* Predicate (grammar), in linguistics
* Predication (philosophy)
* several closely related uses in mathematics and formal logic:
**Predicate (mathematical logic)
**Propositional function
**Finitary relation, o ...
, and a value. For example,
geo:long=50.123456
is a tag for the geographical
longitude
Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lette ...
coordinate whose value is 50.123456. This triple structure is similar to the
Resource Description Framework model for information.
The triple tag format was first devised for geolicious in November 2004, to map
Delicious bookmarks, and gained wider acceptance after its adoption by Mappr and GeoBloggers to map
Flickr
Flickr ( ; ) is an American image hosting and video hosting service, as well as an online community, founded in Canada and headquartered in the United States. It was created by Ludicorp in 2004 and was a popular way for amateur and profession ...
photos. In January 2007, Aaron Straup Cope at Flickr introduced the term ''machine tag'' as an alternative name for the triple tag, adding some questions and answers on purpose, syntax, and use.
Specialized metadata for geographical identification is known as ''
geotagging
Geotagging, or GeoTagging, is the process of adding geographical identification metadata to various media such as a geotagged photograph or video, websites, SMS messages, QR Codes or RSS feeds and is a form of geospatial metadata. This data u ...
''; machine tags are also used for other purposes, such as identifying photos taken at a specific event or naming species using
binomial nomenclature
In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...
.
Hashtags
A hashtag is a kind of metadata tag marked by the prefix
#
, sometimes known as a "hash" symbol. This form of tagging is used on
microblogging
Microblogging is a form of social network that permits only short posts. They "allow users to exchange small elements of content such as short sentences, individual images, or video links",. Retrieved June 5, 2014 which may be the major reason for ...
and
social networking services such as
Twitter
Twitter is an online social media and social networking service owned and operated by American company Twitter, Inc., on which users post and interact with 280-character-long messages known as "tweets". Registered users can post, like, and ...
,
Facebook
Facebook is an online social media and social networking service owned by American company Meta Platforms. Founded in 2004 by Mark Zuckerberg with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dustin Mosk ...
,
Google+
Google+ (pronounced and sometimes written as Google Plus; sometimes called G+) was a social network owned and operated by Google. The network was launched on June 28, 2011, in an attempt to challenge other social networks, linking other Google p ...
,
VK and
Instagram. The hash is used to distinguish tag text, as distinct, from other text in the post.
Knowledge tags
A knowledge tag is a type of
meta-information that describes or defines some aspect of a piece of information (such as a
document
A document is a written, drawn, presented, or memorialized representation of thought, often the manifestation of non-fictional, as well as fictional, content. The word originates from the Latin ''Documentum'', which denotes a "teaching" o ...
,
digital image,
database table
A table is a collection of related data held in a table format within a database. It consists of columns and rows.
In relational databases, and flat file databases, a ''table'' is a set of data elements (values) using a model of vertical colum ...
, or
web page).
Knowledge tags are more than traditional non-hierarchical
keywords or terms; they are a type of
metadata that captures knowledge in the form of descriptions, categorizations, classifications,
semantics
Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comp ...
, comments, notes, annotations,
hyperdata
Hyperdata are data objects linked to other data objects in other places, as hypertext indicates text linked to other text in other places. Hyperdata enables formation of a web of data, evolving from the "data on the Web" that is not inter-related ...
,
hyperlinks
In computing, a hyperlink, or simply a link, is a digital reference to data that the user can follow or be guided by clicking or tapping. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text wi ...
, or references that are collected in tag profiles (a kind of
ontology
In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality.
Ontology addresses questions like how entities are grouped into categories and which of these entities exi ...
).
These tag profiles reference an information resource that resides in a distributed, and often heterogeneous, storage repository.
Knowledge tags are part of a
knowledge management
Knowledge management (KM) is the collection of methods relating to creating, sharing, using and managing the knowledge and information of an organization. It refers to a multidisciplinary approach to achieve organisational objectives by making ...
discipline that leverages
Enterprise 2.0
Web 2.0 (also known as participative (or participatory) web and social web) refers to websites that emphasize user-generated content, ease of use, participatory culture and interoperability (i.e., compatibility with other products, systems, and ...
methodologies for users to capture insights, expertise, attributes, dependencies, or relationships associated with a data resource.
Different kinds of knowledge can be captured in knowledge tags, including factual knowledge (that found in books and data), conceptual knowledge (found in perspectives and concepts), expectational knowledge (needed to make judgments and hypothesis), and methodological knowledge (derived from reasoning and strategies).
These forms of
knowledge
Knowledge can be defined as Descriptive knowledge, awareness of facts or as Procedural knowledge, practical skills, and may also refer to Knowledge by acquaintance, familiarity with objects or situations. Knowledge of facts, also called pro ...
often exist outside the data itself and are derived from personal experience, insight, or expertise. Knowledge tags are considered an expansion of the information itself that adds additional value, context, and meaning to the information. Knowledge tags are valuable for preserving organizational intelligence that is often lost due to
turnover, for sharing knowledge stored in the minds of individuals that is typically isolated and unharnessed by the organization, and for connecting knowledge that is often lost or disconnected from an information resource.
Advantages and disadvantages
In a typical tagging system, there is no explicit information about the meaning or
semantics
Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comp ...
of each tag, and a user can apply new tags to an item as easily as applying older tags.
Hierarchical classification systems can be slow to change, and are rooted in the culture and era that created them; in contrast, the flexibility of tagging allows users to classify their collections of items in the ways that they find useful, but the personalized variety of terms can present challenges when searching and browsing.
When users can freely choose tags (creating a
folksonomy
Folksonomy is a classification system in which end users apply public tags to online items, typically to make those items easier for themselves or others to find later. Over time, this can give rise to a classification system based on those tags ...
, as opposed to selecting terms from a
controlled vocabulary
Control may refer to:
Basic meanings Economics and business
* Control (management), an element of management
* Control, an element of management accounting
* Comptroller (or controller), a senior financial officer in an organization
* Controllin ...
), the resulting metadata can include
homonym
In linguistics, homonyms are words which are homographs (words that share the same spelling, regardless of pronunciation), or homophones ( equivocal words, that share the same pronunciation, regardless of spelling), or both. Using this definiti ...
s (the same tags used with different meanings) and
synonyms (multiple tags for the same concept), which may lead to inappropriate connections between items and inefficient searches for information about a subject. For example, the tag "orange" may refer to the
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
or the
color
Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...
, and items related to a version of the
Linux kernel may be tagged "Linux", "kernel", "Penguin", "software", or a variety of other terms. Users can also choose tags that are different
inflection
In linguistic morphology, inflection (or inflexion) is a process of word formation in which a word is modified to express different grammatical categories such as tense, case, voice, aspect, person, number, gender, mood, animacy, and ...
s of words (such as singular and plural), which can contribute to navigation difficulties if the system does not include
stemming
In linguistic morphology and information retrieval, stemming is the process of reducing inflected (or sometimes derived) words to their word stem, base or root form—generally a written word form. The stem need not be identical to the morpholog ...
of tags when searching or browsing. Larger-scale folksonomies address some of the problems of tagging, in that users of tagging systems tend to notice the current use of "tag terms" within these systems, and thus use existing tags in order to easily form connections to related items. In this way, folksonomies may collectively develop a partial set of tagging conventions.
Complex system dynamics
Despite the apparent lack of control, research has shown that a simple form of shared vocabulary emerges in social bookmarking systems. Collaborative tagging exhibits a form of
complex systems dynamics (or
self-organizing
Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order and disorder, order arises from local interactions between parts of an initially disordered system. The process can be spon ...
dynamics).
Thus, even if no central controlled vocabulary constrains the actions of individual users, the distribution of tags converges over time to stable
power law distributions.
Once such stable distributions form, simple
folksonomic vocabularies can be extracted by examining the
correlations that form between different tags. In addition, research has suggested that it is easier for
machine learning
Machine learning (ML) is a field of inquiry devoted to understanding and building methods that 'learn', that is, methods that leverage data to improve performance on some set of tasks. It is seen as a part of artificial intelligence.
Machine ...
algorithms to learn tag semantics when users tag "verbosely"—when they annotate resources with a wealth of freely associated, descriptive keywords.
Spamming
Tagging systems open to the public are also open to tag spam, in which people apply an excessive number of tags or unrelated tags to an item (such as a
YouTube
YouTube is a global online video sharing and social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by Google, and is the second mo ...
video) in order to attract viewers. This abuse can be mitigated using human or statistical identification of spam items. The number of tags allowed may also be limited to reduce spam.
Syntax
Some tagging systems provide a single
text box
type=search
placeholder=An example text box, which can be used to search the English Wikipedia.
A text box (input box), text field or text entry box is a control element of a graphical user interface, that should enable the user to input ...
to enter tags, so to be able to
tokenize
In computer science, lexical analysis, lexing or tokenization is the process of converting a sequence of characters (such as in a computer program or web page) into a sequence of ''lexical tokens'' ( strings with an assigned and thus identified ...
the string, a
separator must be used. Two popular separators are the
space character
In computer programming, whitespace is any character or series of characters that represent horizontal or vertical space in typography. When rendered, a whitespace character does not correspond to a visible mark, but typically does occupy an area ...
and the
comma. To enable the use of separators in the tags, a system may allow for higher-level separators (such as
quotation marks) or
escape characters. Systems can avoid the use of separators by allowing only one tag to be added to each input
widget at a time, although this makes adding multiple tags more time-consuming.
A syntax for use within
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 JavaSc ...
is to use the rel-tag
microformat
Microformats (μF) are a set of defined HTML classes created to serve as consistent and descriptive metadata about an element, designating it as representing a certain type of data (such as contact information, geographic coordinates, events ...
which uses the
''rel'' attribute with value "tag" (i.e.,
rel="tag"
) to indicate that the linked-to page acts as a tag for the current context.
See also
*
Annotation
An annotation is extra information associated with a particular point in a document or other piece of information. It can be a note that includes a comment or explanation. Annotations are sometimes presented in the margin of book pages. For anno ...
*
Collective intelligence
*
Concept map
A concept map or conceptual diagram is a diagram that depicts suggested relationships between concepts. Concept maps may be used by instructional designers, engineers, technical writers, and others to organize and structure knowledge.
A conc ...
*
Enterprise bookmarking Enterprise bookmarking is a method for Web 2.0 users to tag, organize, store, and search bookmarks of both web pages on the Internet and data resources stored in a distributed database or fileserver. This is done collectively and collaboratively i ...
*
Enterprise social software Enterprise social software (also known as or regarded as a major component of Enterprise 2.0), comprises social software as used in "enterprise" (business/commercial) contexts. It includes social and networked modifications to corporate intranets ...
*
Expert system
*
Explicit knowledge
Explicit knowledge (also expressive knowledge) is knowledge that can be readily articulated, codified, stored and accessed. It can be expressed in formal and systematical language and shared in the form of data, scientific formulae, specifications ...
*
Human–computer interaction
Human–computer interaction (HCI) is research in the design and the use of computer technology, which focuses on the interfaces between people (users) and computers. HCI researchers observe the ways humans interact with computers and design te ...
*
Information ecology Information ecology is the application of ecological concepts for modeling the information society. It considers the dynamics and properties of the increasingly dense, complex and important digital informational environment. "Information ecology" of ...
*
Knowledge transfer
*
Knowledge worker
Knowledge workers are workers whose main capital is knowledge. Examples include programmers, physicians, pharmacists, architects, engineers, scientists, design thinkers, public accountants, lawyers, editors, and academics, whose job is ...
*
Management information system
A management information system (MIS) is an information system used for decision-making, and for the coordination, control, analysis, and visualization of information in an organization. The study of the management information systems involves peo ...
*
Metaknowledge
Meta-knowledge or metaknowledge is knowledge about knowledge.
Some authors divide meta-knowledge into orders:
* ''zero order meta-knowledge'' is knowledge whose domain is not knowledge (and hence zero order meta-knowledge is not meta-knowledge ''p ...
*
Organisational memory
*
RRID
*
Semantics
Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comp ...
*
Semantic web
*
Social network aggregation
Social network aggregation is the process of collecting content from multiple social network services into one unified presentation. The task is often performed by a social network aggregator, such as Hootsuite or FriendFeed, which pulls together ...
*
Subject (documents)
*
Subject indexing
Subject indexing is the act of describing or classifying a document by index terms, keywords, or other symbols in order to indicate what different documents are ''about'', to summarize their contents or to increase findability. In other words, i ...
References
{{DEFAULTSORT:Tag (Metadata)
Collective intelligence
Computer jargon
Information retrieval techniques
Knowledge representation
Metadata
Reference
Web 2.0