Identification

What is a thing called?

tension: Names that locate (URLs) against names that stay stable (content hashes, DOIs, DIDs); whether a web address names a page or the thing it describes (httpRange-14).
also: Naming, Identity, Addressing
scheme: design issues

Threads (6)

Long-running problems under this issue, told step by step. All threads.

Names that outlive their hosts 1994–2022 open 9 steps
How can a name keep working after the server, the company or the domain behind it is gone?
Page or thing? 1998–2012 largely settled 9 steps
When you look up an http URI, have you got the thing it names, or a document about that thing?
Same thing, many names 2004–2026 open 6 steps
When two datasets name the same thing, how do we say so without claiming more than we mean?
Who issues your name online? 2000–2026 open 11 steps
Should people be known online by accounts that platforms issue, or by names they control themselves?
Who runs the registry? 1957–2026 open 10 steps
When everyone depends on one set of identifiers, who issues them, on what terms, and what happens when the registry runs out, changes hands or closes its code?
From catalogue card to web data 1876–2024 open 11 steps
Can library catalogue records, built for card drawers and MARC, become first-class data on the Web?

Who answered it

This issue's row of the map: which traditions' works mainly answer it, and the earliest from each.

Works on this issue by tradition
tradition	works	earliest
Hypertext
Knowledge representation	3	In Defense of Ambiguity 2008
Databases
Machine learning
Web standards	21	URI 1994
Search	1	Google Social Graph API 2008
Social web	5	Facebook 2004
Open knowledge	2	Open Library 2007
Decentralized web	5	OpenID 2005
Libraries, archives and museums	6	Handle System 1994
Life sciences
Media	2	IMDb 1990
Geospatial	8	Satellite Catalog Number 1957
Commerce and supply chain	6	Barcode 1949
Government and law	4	legislation.gov.uk 2010
Finance	3	International Securities Identification Number 1981
Industry and engineering

12 of 17 traditions have taken up this question as a work's main issue; a work in several traditions counts in each. Same counts as the full map.

Timeline

Works on this question, its main or a secondary one, each shown once in date order; filter by tradition to follow one community. Bars run from start to end where both are known; marks people, projects and organizations still active. 10 entries have no date and are not shown. Hover over or focus an entry to draw its links. Scroll sideways, or use the decades above.

Lineage (51)

Works whose main question this is, by type, oldest first.

Concepts 8

Barcode 1949 concept technique
A machine-readable pattern of lines that encodes a number, patented by Woodland and Silver in 1952 and put on groceries from 1974; it gave everyday objects identifiers that machines could read.
URI 1994 concept ★ seminal principle
Global name for any resource, from a web page to a person or an idea; the foundation the rest of the stack builds on. IRIs extend URIs to Unicode.
Internet of Things 1999 concept vision
Physical objects that identify themselves and report data over networks without people typing it in; the term was coined by Kevin Ashton in 1999 about RFID in supply chains.
httpRange-14 2002 concept ★ seminal debate
Long-running W3C Technical Architecture Group issue over whether an HTTP URI names a web page or the thing the page describes, such as a person.
Content addressing concept technique
Naming data by a cryptographic hash of its content instead of by where it is stored. It is the main alternative to location-based URIs: the name says what a thing is, not where it lives.
Dereferenceable URI concept principle
URI that can be looked up over HTTP to get data about the thing it names, which in turn links to further URIs: 'follow your nose'.
Identity and co-reference concept debate
The problem of recognising when different names refer to the same thing. OWL's owl:sameAs states it, but used loosely across datasets it merges things that are only similar.
Self-sovereign identity concept principle
Approach to digital identity in which people hold and control their own identifiers and credentials instead of relying on a central provider.

Writings 9

Cool URIs don't change 1998 writing ★ seminal principle
Tim Berners-Lee's 1998 note arguing that a URI, once published, should keep working indefinitely, and that breaking links is a choice made by poor design rather than an accident of technology.
httpRange-14 resolution 2005 writing ★ seminal technique
Roy Fielding's June 2005 message announcing the W3C TAG's answer to httpRange-14: a URI that answers with a 2xx response names an information resource, while one that answers with a 303 redirect may name anything.
Cool URIs for the Semantic Web 2008 writing ★ seminal technique
W3C Interest Group Note (2008) giving publishers two recipes for URIs that name things rather than pages: hash URIs, and 303 redirects based on the httpRange-14 resolution.
In Defense of Ambiguity 2008 writing debate
2008 paper by Pat Hayes and Harry Halpin arguing that reference is ambiguous in any language, so Web architecture cannot make what a URI names fully unambiguous, and that a redirect alone does not settle it.
When owl:sameAs Isn't the Same: An Analysis of Identity in Linked Data 2010 writing ★ seminal
2010 ISWC paper showing that owl:sameAs links between Linked Data sets are often used to mean 'similar' or 'related' rather than strict identity, and proposing finer-grained alternatives.
Call for proposals to amend the httpRange-14 resolution 2012 writing debate
Jonathan Rees's February 2012 call, for the W3C TAG, for proposals to change or withdraw the 2005 resolution, citing the cost of 303 redirects: extra round trips, caching, and hosts that cannot send them.
Wikidata: A Free Collaborative Knowledgebase 2014 writing
Communications of the ACM article by Vrandečić and Krötzsch introducing Wikidata's design and goals.
The Path to Self-Sovereign Identity 2016 writing principle
Christopher Allen's essay setting out ten principles for digital identity controlled by the individual.
sameAs.cc: The Closure of 500M owl:sameAs Statements 2018 writing technique
2018 ESWC paper that collected about 559 million owl:sameAs statements from a 2015 crawl of Linked Data, computed which names they make equivalent, and published the result with an error score for each link.

Standards 20

Satellite Catalog Number 1957 standard
Sequential number given by the US military to every object it tracks in orbit, starting with Sputnik 1's rocket (1) and satellite (2). It ran out of five digits on 11 July 2026, forcing the 'Alpha-5' workaround and a move to nine-digit formats.
International Designator 1963 standard
Identifier for a spacecraft by launch year, launch number and piece, such as 1990-037B for the Hubble Space Telescope; in use since 1963, replacing a Greek-letter scheme from Harvard.
Universal Product Code 1973 standard ★ seminal
The US grocery industry's product barcode and numbering standard, chosen on 3 April 1973 from IBM's design; the first scan was a pack of Wrigley's gum in Troy, Ohio, on 26 June 1974.
Global Trade Item Number 1977 standard
GS1's family of product numbers, joining the American UPC with the European Article Number from 1977; it is the number in retail barcodes and the base of the GS1 system.
International Securities Identification Number 1981 standard
12-character code identifying a security for clearing, reporting and settlement, first used in 1981 and standardised as ISO 6166 after the G30 recommended it in 1989.
WGS 84 1984 standard
The geodetic reference system of 1984 behind GPS: the shape of the Earth and origin against which most latitudes and longitudes on the Web, from the W3C Geo vocabulary to GeoJSON, are given.
Handle System 1994 standard
System for assigning and resolving persistent identifiers, developed and operated by CNRI; DOIs are Handle System handles under the prefix 10.
DOI 2000 standard ★ seminal
Persistent identifier for documents and data, introduced in 2000. A DOI names the object rather than where it is stored, and resolves through doi.org; it is built on the Handle System and fits within the URI system.
Architecture of the World Wide Web, Volume One 2004 standard ★ seminal
W3C Technical Architecture Group's account of the Web's architecture: identifying resources by URI, interacting with them through representations, and data formats; a W3C Recommendation since 15 December 2004.
OpenID 2005 standard
Protocol created by Brad Fitzpatrick in 2005 that lets people sign in to many sites with an identity they control, a URL rather than a site-specific account; later versions built on OAuth.
EIDR 2010 standard
The film and television industry's registry of identifiers, founded in October 2010 by MovieLabs, CableLabs, Comcast and Rovi. Every title, edit and version gets a DOI, so studios, broadcasters and streaming services can refer to the same thing.
European Case Law Identifier 2011 standard
Identifier for court decisions across the EU, in the form ECLI:country:court:year:number, with a minimum set of shared metadata; set out in EU Council conclusions published in April 2011.
European Legislation Identifier 2012 standard
Identifiers and an ontology for national and EU legislation, so each law and version has a stable web address and machine-readable metadata; the EU Council invited its adoption in October 2012.
Legal Entity Identifier 2012 standard
20-character identifier for every company, fund or government body that takes part in financial transactions, defined in ISO 17442. The G20 called for it in 2011 after the 2008 crisis showed that regulators could not tell who was exposed to whom; the first LEIs were issued in December 2012. Its records say who is who and who owns whom, and are published openly, including as RDF.
Financial Instrument Global Identifier 2014 standard
Open identifier for financial instruments of every kind, from shares to currencies; it began as Bloomberg's open symbology in 2009 and became an Object Management Group standard in 2014, free to use, unlike most proprietary securities codes.
Open Location Code 2014 standard
Open encoding, published by Google in October 2014, that turns coordinates into short codes such as 8FVC9G8F+6X; a free alternative to proprietary address grids.
Spatial Data on the Web Best Practices 2017 standard
Joint W3C and OGC guidance, first published in 2017, for putting spatial data on the Web rather than in downloads; its first practice is to give places and spatial things persistent HTTP URIs.
GS1 Digital Link 2018 standard ★ seminal
GS1 standard for writing product identifiers such as GTINs as web URIs, so that a barcode or QR code on a pack resolves to information about the product; ratified in August 2018. It puts Linked Data identifiers on everyday goods.
Decentralized Identifiers 2022 standard ★ seminal
W3C specification for identifiers that their subject can create and control without a central registry. DID 1.0 became a Recommendation in July 2022; DID 1.1 reached Candidate Recommendation in March 2026.
Electronic Product Code standard
Identifier for each individual physical object, not just each product type, designed to be carried on RFID tags; it came out of MIT's Auto-ID Center and is maintained by GS1.

Projects 14

IMDb 1990 project ★ seminal
Database of films, television and the people who make them. It began in October 1990 as fan lists on the rec.arts.movies newsgroup, became a company in 1996 and was bought by Amazon in 1998; its data is proprietary, released only for non-commercial use, yet other databases link to its title and name IDs.
VIAF 1998 project
Service that links the name authority files of national libraries and merges records for the same person or organization into one cluster. Begun in 1998 by the Library of Congress, the Deutsche Nationalbibliothek and OCLC; it now draws on more than 50 organizations in over 30 countries.
Facebook 2004 project
Social network launched in February 2004. Its profiles, pages and 'Log in with Facebook' made a Facebook account a de facto identifier for people and organizations, and its Open Graph protocol turned web pages into objects in its own graph.
GeoNames 2005 project ★ seminal
Database of more than 25 million place names, founded in 2005 and published under a Creative Commons attribution licence. Each place has a stable URI that returns a web page or RDF, with links to Wikipedia, which made it the usual place identifier in linked data.
Twitter 2006 project
Microblogging service launched in 2006, renamed X in 2023. Its usernames serve as identifiers for people and organizations on about 467,000 Wikidata items; it ended free access to its API in February 2023.
Open Library 2007 project
Internet Archive project to build 'one web page for every book ever published', begun in 2007 with Aaron Swartz.
Google Social Graph API 2008–2012 project
Google service launched in February 2008 that crawled XFN, FOAF and other public markup to report who links to whom across the Web; retired in April 2012 for lack of use.
Log in with Facebook 2008 project
Facebook's sign-in for other sites, unveiled as Facebook Connect in July 2008 and generally available from December 2008, which made a Facebook account a login across the Web.
id.loc.gov 2009 project
Library of Congress Linked Data Service, publishing its authorities and vocabularies at stable URIs; it opened with the Subject Headings in April 2009.
legislation.gov.uk 2010 project
The UK's official online statute book, run by The National Archives and launched in 2010, which publishes every law as a web page and as data, with each page's data a URI suffix away, and exposes the statute book as linked data.
Wikidata 2012 project ★ seminal
Free, collaboratively edited knowledge graph run by the Wikimedia Foundation. It supplies structured data to Wikipedia and the sameAs links on this site.
w3id.org 2013 project
Permanent URL redirect service run by the W3C Permanent Identifier Community Group since 2013. Anyone can claim a path by pull request and point it wherever their data lives; a consortium of organisations has pledged to keep it running.
what3words 2013 project
Proprietary system, launched in July 2013, that names every 3-metre square on Earth with three words. Widely adopted by British emergency services, it is criticised for its closed, patented algorithm, takedowns of reimplementations and addresses that are easily confused.
Pleiades project
Open gazetteer of ancient places, built from the Barrington Atlas of the Greek and Roman World by NYU's Institute for the Study of the Ancient World and the Ancient World Mapping Center; each place has a stable URI, and its data is CC BY.

Also bears on this (32)

Concepts 5

Transclusion 1980 concept technique
Including part of one document in another by reference, so the same content appears in both places and stays linked to its source. Ted Nelson coined the term in 1980.
Linked Data 2006 concept principle
Way of publishing data on the Web with URIs, HTTP and RDF, so that data sets link to one another the way documents do.
FAIR data principles 2016 concept ★ seminal principle
Principles that research data should be findable, accessible, interoperable and reusable, published in Scientific Data in March 2016.
JSON web APIs concept technique
Plain JSON over HTTP with each API defining its own fields, without shared vocabularies or global identifiers; the everyday alternative most developers chose over Linked Data.
Merkle DAG concept formalism
Graph of data blocks in which each block links to others by their content hash, so any change produces new hashes all the way up; a generalisation of the Merkle tree.

Writings 6

Architectural Styles and the Design of Network-based Software Architectures 2000 writing ★ seminal principle
Roy Fielding's 2000 doctoral dissertation at UC Irvine, which defined REST, the architectural style of the Web: resources named by URIs, manipulated through representations over a uniform interface. Most Web APIs since claim descent from it.
Linked Data (Design Issues) 2006 writing ★ seminal principle
Tim Berners-Lee's short Design Issues note setting out four rules for publishing data on the Web with URIs and links.
Thoughts on the Social Graph 2007 writing vision
August 2007 essay by Brad Fitzpatrick and David Recordon arguing that the map of who knows whom should be an open, shared asset rather than locked inside each social network.
Introducing the Knowledge Graph: things, not strings 2012 writing ★ seminal principle
Google blog post by Amit Singhal announcing the Knowledge Graph, which brought the term into wide use.
IPFS – Content Addressed, Versioned, P2P File System 2014 writing ★ seminal
Juan Benet's 2014 paper describing the design of IPFS.
Scholarly Context Not Found: One in Five Articles Suffers from Reference Rot 2014 writing ★ seminal
2014 PLoS ONE study of millions of web links in scholarly articles, finding that about one in five articles cites web resources that have since vanished or changed: link rot measured at scale.

Standards 10

HTTP 1991 standard ★ seminal
Hypertext Transfer Protocol: the Web's request–response protocol for fetching a resource by its URL. Berners-Lee's first version was written up in 1991; HTTP/1.0 and 1.1 followed as IETF RFCs. Looking up a URI to get data about the thing it names depends on it.
PURL 1995 standard ★ seminal
Persistent Uniform Resource Locator: a web address that points at a resolver instead of the resource, so the target can move without breaking links. OCLC introduced it in 1995 and ran purl.org, where Dublin Core and many other vocabularies keep their namespaces, until it handed the service to the Internet Archive in September 2016.
FOAF 2000 standard ★ seminal
RDF vocabulary for describing people, their online accounts and who they know; one of the first widely used Semantic Web vocabularies.
XFN 2003 standard
Microformat from 2003 for marking up how the person behind a link relates to you, such as friend, colleague or met, using the rel attribute; Google's Social Graph API crawled it.
Akoma Ntoso 2004 standard
XML standard for legislative, judicial and executive documents, begun in 2004 by the UN for African parliaments and adopted by OASIS as LegalDocML in August 2018; its identifiers follow the FRBR model of work, expression and manifestation.
Verifiable Credentials Data Model 2019 standard ★ seminal
W3C data model for tamper-evident digital credentials, such as diplomas or licences, that can be checked cryptographically. Version 1.0 became a Recommendation in November 2019, and version 2.0, with its Data Integrity and cryptosuite specifications, in May 2025.
Content Credentials 2021 standard
C2PA's format for cryptographically signed provenance records ('manifests') attached to images, video and other media, recording who made them and how they were edited; version 1.0 appeared in December 2021.
AT Protocol 2022 standard
Protocol behind Bluesky. Every account is a DID with a domain name as its handle. Its schema language, Lexicon, deliberately avoids RDF and JSON-LD in favour of strict, versioned schemas.
GS1 Web Vocabulary standard
GS1's terms for products, organisations and locations published as Linked Data and designed as an extension to schema.org.
IPLD standard
Data model for linking data by content hash rather than by location; the data layer under IPFS, and the basis of AT Protocol's repository format.

Projects 11

Getty Vocabularies 1981 project
Thesauri for art and cultural heritage: the Art & Architecture Thesaurus (from 1981), the Thesaurus of Geographic Names and the Union List of Artist Names. Published as linked open data from February 2014 under an open attribution licence.
World Wide Web 1990 project ★ seminal
Hypertext system of documents linked by URLs and served over HTTP, built by Tim Berners-Lee and Robert Cailliau at CERN from 1990.
CDDB c. 1993 project
Database of CD track listings, started by Ti Kan around 1993 and filled by users who believed it would stay free. It was sold in 1998, renamed Gracenote in 2000 and moved to proprietary terms, which provoked the freedb fork and MusicBrainz.
MusicBrainz 2000 project ★ seminal
Open, volunteer-edited database of music metadata, launched in 2000 in reaction to CDDB's enclosure. Its core data has been in the public domain since 2003, and its identifiers anchor the Music Ontology, BBC Music and Wikidata's music items.
Wayback Machine 2001 project ★ seminal
The Internet Archive's public archive of the Web, open since 25 October 2001 and built from crawls going back to 1996; for many dead links and vanished sites it is the only copy left, kept by a nonprofit funded mainly by donations and grants.
Myspace 2003 project
Social network launched in 2003 that dominated the late 2000s and became where many musicians hosted their songs. In 2019 it confirmed that about 50 million songs uploaded before 2015 were lost in a server migration.
BBC Music and Programmes linked data 2007 project
The BBC's pages for every programme (from 2007) and every artist (beta from July 2008), each a web page and an RDF description. Artists were keyed on MusicBrainz identifiers and linked to DBpedia, so a public broadcaster built on fan-made data.
IndieWeb 2011 project
Community, started with the first IndieWebCamp in 2011, of people who publish on their own domains and connect sites with open standards such as microformats and Webmention, instead of relying on platforms.
Rebooting the Web of Trust 2015–2023 project
Series of design workshops on decentralised identity and trust, started by Christopher Allen in 2015, whose collaboratively written papers fed into DIDs and Verifiable Credentials. The twelfth was held in Cologne in September 2023; the thirteenth, planned for October 2024, was cancelled for lack of support, and the papers now survive on GitHub.
IPFS 2015 project
Peer-to-peer system for storing and sharing files addressed by their content hash, created by Juan Benet; the alpha was released in February 2015.
Digital Product Passport 2024 project
EU scheme under the 2024 Ecodesign Regulation giving products a digital record of what they are made of and how to repair and recycle them, reached through a QR code; batteries are first, from February 2027, and an EU registry opened in July 2026.

People and organizations (58)

Linked to works on this question; the number counts those works.

World Wide Web Consortium (5) · GS1 (4) · Brad Fitzpatrick (2) · Christopher Allen (2) · Denny Vrandečić (2) · Google (2) · Harry Halpin (2) · Library of Congress (2) · Manu Sporny (2) · Markus Krötzsch (2) · OCLC (2) · Pat Hayes (2) · Tim Berners-Lee (2) · Aaron Swartz · Allen Institute for Artificial Intelligence · Amazon · Amy Guy · Bernard Silver · Brewster Kahle · Col Needham · Crossref · Dave Longley · David Recordon · Deborah McGuinness · Drummond Reed · Frank van Harmelen · George Laurer · Global Legal Entity Identifier Foundation · Henry S. Thompson · Ian Jacobs · International DOI Foundation · Internet Archive · Jamie McCusker · Jan Wielemaker · Jeremy Tandy · Joe Raad · John Sheridan · Jonathan Rees · Kevin Ashton · Leo Sauermann · Linda van den Brink · Lydia Pintscher · Marc Wick · Markus Sabadello · Meta Platforms · Gordon and Betty Moore Foundation · Norman Walsh · Norman Joseph Woodland · Open Geospatial Consortium · Payam Barnaghi · Richard Cyganiak · Roy Fielding · Sean Gillies · Timo Homburg · Tom Elliott · Wikimedia Deutschland · Wikimedia Foundation · Wouter Beek