Knowledge representation

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.

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

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

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.

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.

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

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.

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

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

John McCarthy's 1959 paper proposing the 'advice taker', a program that would decide what to do by deducing it from facts and rules stated in formal logic; the founding statement of logic-based knowledge representation.

Collection of early AI research on meaning and language, edited by Marvin Minsky.

M. Ross Quillian's account of a memory model that stores word meanings as a network of linked concepts.

Marvin Minsky's MIT AI Lab memo introducing frames: structures of slots with default values for stereotyped situations.

William Woods's 1975 critique showing that the links in semantic networks had no agreed meaning, mixing up, for example, a class with its members and a definition with an assertion; it set the agenda for giving networks a formal semantics.

Raymond Reiter's 1978 paper formalizing the closed-world assumption: a database may treat any fact it cannot show to be true as false.

Brachman and Schmolze's 1985 account of KL-ONE, a frame-based system with defined concepts and an automatic classifier that places each concept in a subsumption hierarchy; KL-ONE was the first knowledge representation system based on what became description logics.

Levesque and Brachman's 1987 paper showing that reasoning gets dramatically harder as a representation language gets more expressive, and that this trade-off underlies the differences between existing representation formalisms.

Book by Doug Lenat and R.V. Guha on the representation and inference methods of the Cyc project.

Tom Gruber's paper on sharing ontologies between knowledge systems. It contains the definition of an ontology as 'an explicit specification of a conceptualization'.

Step-by-step guide by Natasha Noy and Deborah McGuinness to building an ontology, with examples in Protégé.

Design history of OWL by Horrocks, Patel-Schneider and van Harmelen, tracing it from description logics and RDF.

WWW 2005 paper extending RDF so that a set of statements can be named by a URI and described like any resource. It shows publishers signing their graphs and consumers deciding which graphs to trust.

Book by Jérôme Euzenat and Pavel Shvaiko (2007; second edition 2013) on methods for finding correspondences between the terms of different ontologies, so that data described in one can be used with another.

Jim Hendler's 2007 editorial in IEEE Intelligent Systems, six years after he co-wrote the Scientific American article that promised Semantic Web agents, asking why those agents had not appeared.

WWW 2007 paper presenting YAGO, a knowledge base that attaches facts extracted from Wikipedia to WordNet's taxonomy, with high measured accuracy.

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.

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.

2014 KDD paper by Xin Luna Dong and eight Google colleagues describing a knowledge base built by machine: facts extracted from text, tables and page structure across the Web, combined with existing knowledge bases and given probabilities of being true.

2015 paper by Robert Rovetto in Earth Science Informatics presenting an ontological architecture for data on orbital debris and space situational awareness.

Survey by Aidan Hogan and 17 co-authors of the data models, query languages, reasoning and methods behind knowledge graphs.

Survey proposing three ways to combine language models and knowledge graphs: KG-enhanced LLMs, LLM-augmented KGs, and the two working together.

Simple HTML Ontology Extensions: an early language for writing ontologies and annotating web pages with machine-readable claims, developed at the University of Maryland around 1996; among the first ontology languages made for the Web.

Ontology for museum and cultural heritage documentation from ICOM's documentation committee, first issued in 1999 and an ISO standard since 2006. It describes objects through the events in their history, such as production, acquisition and movement, so that records from different institutions can be integrated.

Ontology language formed in 2001 by merging the American DAML with the European OIL; a thin layer over RDF Schema with description-logic semantics, and the direct basis of OWL.

Logic-based clinical terminology of medical concepts and their relations, released in January 2002 and maintained by SNOMED International.

ISO standard for integrating the life-cycle data of process plants, including oil and gas facilities, with a generic data model (Part 2, 2003) and reference data libraries; Part 8 implements it in OWL and RDF.

W3C language for writing ontologies on the Web, based on description logics. OWL 2 followed in 2009.

Formal ontology joining the librarians' FRBR model with the museums' CIDOC CRM, begun in 2006, so that bibliographic and museum records share one model.

Second version of OWL, adding profiles such as OWL 2 EL, QL and RL for tractable reasoning; a W3C Recommendation since October 2009.

OWL ontology of financial contracts, instruments, parties and their relations, begun after the 2008 crisis as a shared vocabulary for analysis and regulatory reporting; developed by the EDM Council with the Object Management Group and in an open community process since 2020.

Long-running project to hand-encode common-sense knowledge as a logical knowledge base, started at MCC and continued by Cycorp.

Lexical database of English begun in 1985 at Princeton's Cognitive Science Laboratory under George A. Miller: nouns, verbs and adjectives grouped into sets of synonyms linked by relations such as broader and part-of. It became a shared vocabulary for language processing and for knowledge bases such as YAGO.

Free ontology editor from Stanford University, widely used to build OWL ontologies.

Ontology of gene and gene-product functions begun in 1998 by researchers working on fly, mouse and yeast genomes; one of the most used ontologies in biology.

DARPA research programme started in 1999 by Jim Hendler to create machine-readable representations for the Web; its RDF-based DAML language fed directly into OWL.

Annual research conference of the Semantic Web community, held since 2002 after a 2001 symposium at Stanford.

Collective of biomedical ontology developers who share principles for building interoperable ontologies; it has led the OBO effort since 2007.

Knowledge base built at the Max Planck Institute for Informatics that combines facts from Wikipedia with WordNet's taxonomy (later with schema.org's); with DBpedia, one of the first large knowledge bases extracted from Wikipedia.

Private research university in California whose biomedical informatics group develops Protégé.

US Defense Department research agency, which funded the DAML programme and earlier funded Engelbart's work.

American research consortium in Austin, Texas, which hosted the Cyc project from 1984 until 1994.

Austin company founded by Doug Lenat to continue developing Cyc after it left MCC.

American psychologist who founded WordNet at Princeton in 1985.

American AI pioneer at MIT who proposed frames in 1974, a structure of slots and defaults that prefigures classes and properties in ontologies.

American computer scientist who coined the term 'artificial intelligence', created Lisp and proposed representing knowledge in formal logic.

Canadian computer scientist and logician who formalized the closed-world assumption for databases in 1978.

American researcher in natural-language processing and knowledge representation, author of 'What's in a Link' (1975).

British AI researcher at IHMC who edited RDF's model theory (RDF Semantics, 2004) and co-edited OWL's semantics.

MIT computer scientist in artificial intelligence and programming languages since 1964; co-author of 'Information Accountability' (2008).

American AI researcher who designed KL-ONE, the system from which description logics grew.

American AI researcher who began the Cyc project in 1984 to hand-encode common-sense knowledge, and founded Cycorp to continue it.

American linguist who later directed WordNet at Princeton.

Canadian AI researcher whose work with Ronald Brachman set out the trade-off between expressiveness and tractability in knowledge representation.

Stanford biomedical informatician who built the first version of Protégé in 1987 and has led its development since.

American AI researcher who co-wrote 'The Semantic Web' (2001) and, as a DARPA programme manager, ran the DAML programme that fed into OWL.

British computer scientist at Oxford whose work on description logics shaped OWL; he co-edited OWL's formal semantics.

American computer scientist whose 1993 paper gave the much-quoted definition of an ontology as 'an explicit specification of a conceptualization'. He later co-founded Siri.

American computer scientist who co-wrote 'Ontology Development 101' and co-edited the W3C's 2004 OWL overview.

Dutch computer scientist at the Vrije Universiteit Amsterdam who co-edited the W3C's 2004 OWL overview.

Dutch computer scientist at Vrije Universiteit Amsterdam and the main developer of SWI-Prolog; co-author of sameAs.cc (2018).

Indian computer scientist whose work runs from Cyc through Apple's Meta Content Framework and Netscape's RSS to schema.org, which he started at Google.

One of the University of Maryland developers of SHOE, an early ontology language for the Web (around 1996).

German computer scientist who co-created Semantic MediaWiki and Wikidata with Denny Vrandečić; he works on knowledge representation at TU Dresden.

Semantic Web researcher at the University of Chile and lead author of the 2021 survey 'Knowledge Graphs'.

Co-author of 'Unifying Large Language Models and Knowledge Graphs: A Roadmap' (2023).

Chilean computer scientist at the Universidad de Chile and co-author of the formal semantics of SPARQL (2009).

One of the University of Maryland developers of SHOE, an early ontology language for the Web (around 1996).

Computer scientist, now a professor at Télécom Paris, who created YAGO.

Dutch computer scientist at VU Amsterdam who co-chaired the W3C Web Ontology Working Group that produced OWL, with Jim Hendler.

American computer scientist, co-author of the 1985 overview of KL-ONE.

French computer scientist at Inria who co-wrote Ontology Matching (2007) with Pavel Shvaiko.

Co-author of 'Unifying Large Language Models and Knowledge Graphs: A Roadmap' (2023).

One of the University of Maryland developers of SHOE, an early ontology language for the Web (around 1996).

Co-author of 'Unifying Large Language Models and Knowledge Graphs: A Roadmap' (2023).

Cognitive scientist whose 1960s models of semantic memory helped establish semantic networks as a way to represent meaning.

Information scientist who led the development of the CIDOC Conceptual Reference Model and its harmonisation with FRBR.

Computer scientist who worked on the Protégé ontology editor at Stanford, co-wrote 'Ontology Development 101', and co-wrote the 2019 paper introducing Google Dataset Search.

Finnish computer scientist who co-edited the first RDF specification (1999) and co-wrote the 2001 Scientific American article 'The Semantic Web'.

Computer scientist who co-wrote Ontology Matching (2007) with Jérôme Euzenat.

Researcher at Bell Labs who co-edited OWL's formal semantics and co-wrote the design history of OWL.

Researcher who proposed ontologies for orbital debris and space situational awareness data from 2015.

One of the University of Maryland developers of SHOE, an early ontology language for the Web (around 1996).

Researcher at INRIA who co-edited the W3C ODRL Information Model 2.2 (2018).

Co-author of 'Unifying Large Language Models and Knowledge Graphs: A Roadmap' (2023).

Co-author of 'Unifying Large Language Models and Knowledge Graphs: A Roadmap' (2023).

Co-author of 'Unifying Large Language Models and Knowledge Graphs: A Roadmap' (2023).