What I make of it
The most depended-upon ontology in OBO — 35 dependents. It defines the relations everything else reuses.
RO (Relation Ontology)
Ontology / Vocabulary
Cross Domain
openly published
RO is a collection of relations intended primarily for standardization across ontologies in the OBO Foundry and wider OBO library. It incorporates ROCore upper-level relations such as part of as well as biology-specific relationship types such as develops from ....
Other cross domain data models
BFO (Basic Formal Ontology)
Ontology / Vocabulary
BPMN (Business Process Model and Notation)
Metadata Model
Creative Commons Rights Expression Language (ccREL)
Ontology / Vocabulary
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Exchange Schema
CMMN (Case Management Model and Notation)
Metadata Model
W3C CSV on the Web (CSVW)
Metadata Model
Data Vault 2.0
Metadata Model
DMN (Decision Model and Notation)
Metadata Model
Event Ontology
Ontology / Vocabulary
FOAF
Ontology / Vocabulary
Frictionless Data Package / Table Schema
Metadata Model
IAO (Information Artifact Ontology)
Ontology / Vocabulary