Definition. A knowledge graph is a structured representation of knowledge where entities (people, places, things, concepts) are nodes and their relationships are edges. It uses shared identifiers and meaning (often via RDF and OWL) so that different datasets can connect, be queried (SPARQL) and reasoned over consistently.
Key ideas
- Semantics-first: data is described with vocabularies/ontologies (classes, properties, constraints).
- Graph-native: knowledge = nodes (entities) + edges (relations) + optional labels/weights.
- Interoperability: globally unique IRIs and shared schemas enable linking across sources.
- Query & reasoning: graph patterns via SPARQL; inference with RDFS/OWL rules.
- Evolution-friendly: graphs can grow incrementally without rigid table migrations.
Typical components
- Data model: RDF triples/quads or labeled property graphs; mappings from relational/JSON.
- Vocabulary: classes & properties (e.g., schema.org, FOAF, SKOS) and custom ontologies.
- Storage & services: triplestores / graph DBs, SPARQL endpoints, APIs.
- Governance: provenance (PROV), versioning, data quality, access control.
Use cases
- Search & recommendations: entity understanding, disambiguation, related-entity surfacing.
- Enterprise data integration: unify silos with a shared semantic layer.
- Analytics & reasoning: impact analysis, compliance checks, root-cause paths.
- Content & media: topic maps, editorial linking, rights/metadata management.
Mini example
Triples (subject–predicate–object):
<http://example.org/person/123> a schema:Person .
<http://example.org/person/123> schema:name "Ada Lovelace" .
<http://example.org/person/123> schema:knows <http://example.org/person/456> .Querying who Ada knows (SPARQL):
SELECT ?friendName WHERE {
<http://example.org/person/123> schema:knows ?friend .
?friend schema:name ?friendName .
}Related terms
FAQ
Is a knowledge graph the same as a graph database?
Not necessarily. A knowledge graph is a model + meaning (semantics and governance). It can be stored in a triplestore or in a property-graph database; the key is that its nodes/edges are semantically defined.
Do I need RDF?
RDF is the most common standard for semantic interoperability. Some projects start with property graphs and later map to RDF for linking and publishing.
Further reading
- schema.org (core web vocabulary)
- W3C RDF, RDFS, OWL, SPARQL specifications
