Concepts

Hypothetical desk-sized device for storing books, records and letters on microfilm and joining them into 'associative trails'. It was never built.

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.

Graph of concepts joined by labelled relations, used to represent meaning; first proposed by Richard Richens in 1956 and developed by Quillian and others in the 1960s.

Text containing links that let a reader jump to other text. Ted Nelson coined the word in the 1960s; the idea goes back to the memex.

Model of data as relations, that is tables of rows with named columns, queried by declarative operations on whole sets; proposed by E.F. Codd and the basis of SQL databases.

'Everything is related to everything else, but near things are more related than distant things': Waldo Tobler's 1970 principle, which underlies spatial interpolation and much of geographic reasoning.

Knowledge structures of slots with default values describing stereotyped situations, proposed by Marvin Minsky in 1974.

Way of modelling a domain as entities, their attributes and the relationships between them, drawn as ER diagrams; introduced by Peter Chen in 1976 as a unified view of the network, relational and entity-set models.

The risk that debris in low Earth orbit reaches a density where collisions create more debris faster than it decays, making orbits unusable: a tragedy of the commons in space.

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.

Decentralised trust model in which people vouch for each other's keys instead of relying on a central authority; put forward by Phil Zimmermann for PGP in 1992.

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.

Tim Berners-Lee's vision of a Web whose data carries machine-readable meaning, built on standards such as RDF and OWL.

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.

Tim Berners-Lee's diagram of the Semantic Web as layers, first shown in his XML 2000 keynote in December 2000: Unicode and URIs at the base, then XML, RDF and RDF Schema, an ontology vocabulary, logic, proof and trust, with digital signatures alongside. W3C redrew it as standards arrived, adding query and rules.

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.

Classification that emerges from many users freely tagging content; the term was coined by Thomas Vander Wal in 2004 and became the bottom-up counterpoint to formal ontologies.

Set of triples given its own URI, so that statements can be made about the set, which is how provenance and context are recorded; stored as quads.

Way of publishing data on the Web with URIs, HTTP and RDF, so that data sets link to one another the way documents do.

A word prefixed with '#' that groups posts by topic. Chris Messina proposed it on Twitter in August 2007; it became the most widely used folksonomy, a vocabulary made by its users rather than designed in advance.

Linked Data published under an open licence. Berners-Lee's 2010 five-star scheme rates open data from 'available in any format' up to 'linked to other data'.

Smallest unit of publishable scientific information: a single assertion written as RDF named graphs, bundled with its provenance and publication details so it can be cited and credited on its own.

Principles that research data should be findable, accessible, interoperable and reusable, published in Scientific Data in March 2016.

Free tagging by users combined with volunteers who link synonymous tags to canonical ones, keeping the users' words while adding a controlled structure; named by Julia Bullard.

Software that keeps the primary copy of a user's data on their own devices and syncs it with others, so it works offline and the user keeps ownership.

Retrieval-augmented generation in which a language model answers from a knowledge graph built over the source texts, rather than from isolated text chunks.

Framework proposed by Creative Commons in June 2025 for dataset holders to state, in machine-readable form, how they want their content reused by AI systems; partly legal and partly a social expectation.

Data too large, fast-moving or varied for ordinary databases, and the methods for drawing value from it by analysis at scale; the term spread around 2010 as companies mined logs, clicks and sensor data.

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.

Agreed list of terms for indexing and retrieval, so that one subject is always described the same way.

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'.

Family of decidable logics for describing concepts and their relations; the formal basis of OWL.

Machine-readable data inside ordinary HTML pages, written as microformats, RDFa, microdata or JSON-LD and usually using the schema.org vocabulary.

Deriving facts that follow from stated ones plus a schema or ontology, for example that a member of a subclass is also a member of its superclass.

Classification that describes a subject by combining independent facets, such as topic, place and time, instead of placing it in one fixed hierarchy.

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.

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.

Graph of entities and the relations between them, used to integrate and query data; the term spread after Google's 2012 Knowledge Graph.

Graph model in which nodes and relationships carry labels and key–value properties; the model behind Neo4j and GQL, and the main rival to RDF for graph data.

Neural language model trained on very large text collections; since the early 2020s the main way software works with unstructured text.

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.

Data that describes other data or documents, such as author, date, subject or format.

AI that combines neural networks with symbolic knowledge such as rules and knowledge graphs; it drew new attention in the 2020s as a way to ground large language models.

Formal description of the concepts in a domain and the relations between them, which software can use to reason about data.

Scale of increasingly formal knowledge organization, from catalogues and glossaries through thesauri and taxonomies to logic-based ontologies, drawn to clarify the many things called 'ontologies'.

The rule that a fact missing from the data is unknown, not false. RDF and OWL assume it, unlike most databases.

Storage that a person controls, from which applications read and write data with permission, instead of each application keeping its own copy.

Technique in which a language model first retrieves relevant documents or data and then generates its answer from them.

The right to have personal information removed from search results or erased by those who hold it, established for search engines by the EU Court of Justice in 2014 and as the right to erasure in Article 17 of the GDPR.

Approach to digital identity in which people hold and control their own identifiers and credentials instead of relying on a central provider.

The subject–predicate–object statement that is the basic unit of RDF.

Program that acts on a person's behalf, for example finding and booking a service; the payoff promised by the 2001 Scientific American article.

Classification of things or concepts into a hierarchy of categories.

Controlled vocabulary whose terms are linked by broader, narrower, related and preferred-term relations.

Database built to store RDF triples and answer SPARQL queries; Virtuoso is one example.

Links that both ends know about, so a document can show what links to it. Central to Xanadu; the Web's links are one-way.

Ontology of very general categories, such as object, process and quality, shared across domains. Examples include Cyc's upper ontology, BFO, DOLCE and SUMO.