Formalism

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.

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.

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.

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.

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.

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.

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.

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

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

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

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

E.F. Codd's 1970 paper in Communications of the ACM proposing that data be organized as relations (tables), independently of how it is stored.

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

Peter Chen's paper in the first issue of ACM Transactions on Database Systems, proposing to model data as entities and the relationships between them.

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.

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

2007 paper by Yves Raimond, Samer Abdallah, Mark Sandler and Frédérick Giasson at ISMIR presenting the Music Ontology, a framework for editorial, cultural and acoustic information about music on the Semantic Web.

2008 EKAW paper by Martin Hepp presenting GoodRelations, an ontology for describing what businesses offer, at what price and on what terms.

Paper by Pérez, Arenas and Gutiérrez giving SPARQL a compositional formal semantics and proving the complexity of evaluating it; general SPARQL patterns are PSPACE-complete.

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

Olaf Hartig's 2017 paper proposing to nest RDF triples, so a statement can carry metadata such as a source or a certainty score without standard reification's bloat. It led to RDF-star and to triple terms in RDF 1.2.