DBpedia is derived from Wikipedia containing over 2 billion RDF triples.
Freebase has relations between people and their nationality, or locations, and other locations they are contained in.
WordNet offer useful ontological relations that express hierarchical relations between words or concepts.

State University of New York at Stony Brook

Relation extraction is the first step of the information extraction process.
Within this step, we find and classify semantic relations among entities mentioned in a text.

Relation Extraction

An on-going but a helpful book resource about NLP
https://web.stanford.edu/~jurafsky/slp3/

Speech and Language Processing (3rd ed. draft) 

Semantic relations example

A model-based view of the relations and entities example

Ontology

An Resource description Framework is a tuple of entity-relation-entity, called a subject-predicate-object expression.
For example, Golden Gate Park-location-San Francisco.
Times Square-location-New York City.

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