aka semantic network, semantic web

There are a lot of fuzz around the subject and there is no one widely recognised definition. But here is definition which is good in a given context:

KG definition

Knowledge graph - a Graph of data intended to accumulate and convey knowledge of the real world, whose nodes represent entities of interest and whose edges represent potentially different relations between these entities.

Knowledge. While many definitions for knowledge have been proposed, we refer to what Nonaka and Takeuchi call “explicit knowledge,” i.e., something that is known and can be written down

From https://dl.acm.org/doi/fullHtml/10.1145/3447772 (https://arxiv.org/pdf/2003.02320.pdf).

Other definitions of KG:

Ontology definition

In computing, an ontology is then a concrete, formal representation—a convention—on what terms mean within the scope in which they are used (e.g., a given domain). Like all conventions, the usefulness of an ontology depends on how broadly and consistently it is adopted and how detailed it is. Knowledge graphs that use a shared ontology will be more interoperable.

From https://dl.acm.org/doi/fullHtml/10.1145/3447772 (https://arxiv.org/pdf/2003.02320.pdf).

Again a lot of fuzz around the subject. Based on some descriptions it is something magical. I rather prefer to think about it as knowledge graph about other knowledge graphs. And in this sense ontologies can form a hierarchy. And there are top-level ontologies - the most abstract ontologies.

Top level ontologies

aka Upper, Foundational, Generic

Scientific papers