Principle: Relations (principle 7)

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Summary

Existing relations MUST be reused. New relations SHOULD be submitted to the Relations Ontology (RO).

Purpose

To facilitate interoperability between multiple ontologies, especially with respect to logical inference, because a reasoner can only detect logical inconsistencies between ontologies and infer new axioms if the ontologies use the same relations (aka object properties).

Recommendations and Requirements

For any given relation need, each OBO ontology MUST reuse a relation from the Relations Ontology (RO) or other ontology if the appropriate relation already exists, rather than declaring new a relation that holds the same meaning. Where it makes sense for an ontology to declare a new relation in its own ID space and there is a RO relation that is logically a super-property of the new relation, the new relation MUST be asserted to be a sub-property of the RO relation. In such cases, it is requested that there still be coordination with RO, for example in the form of an issue submitted to the RO tracker.

Implementation

Reusing relations

‘Reuse’ means that the actual existing-relation PURL is used. Ontology developers should be aware that (in rare instances) relations can evolve over time and previous relations might become obsolete. This means developers should monitor the state of the relations they use. The Relations Ontology MUST be the first source for appropriate relations, and ontology developers SHOULD, with due diligence, search RO for needed relations. If a necessary relation cannot be found within RO, then the developers MUST search other OBO ontologies for reasonable candidates using, for example, an ontology search engine such as Ontobee or OLS.

Creating New Relations

The appropriate home for a new relation (‘R’) will depend on multiple factors, including the general applicability of ‘R’ beyond its use by developers of the ‘R’-proposing ontology (‘O’), and with consideration of the domain and range for ‘R’:

  • If both the domain and range of ‘R’ are classes in the same ontology ‘O’ as ‘R’, ‘R’ MAY be kept in ‘O’;
  • If either the domain or range of ‘R’ are classes not in ‘O’, and ‘R’ does not seem to be general enough for use by other ontologies, ‘R’ MAY be kept in ‘O’;
  • If ‘R’ seems generally usable (that is, could potentially be used by ontologies other than ‘O’), the relation SHOULD be submitted to RO;
  • For any ‘R’ not submitted to RO, if a suitable RO parent (‘P’) exists, then ‘R’ MUST be declared a sub-property of ‘P’;
  • An effort to specify a domain and range for ‘R’ SHOULD be made, though caution is advised to ensure that each is neither too broad nor too specific.

While it is never a bad idea to submit a new relation to RO, if there are any doubts about how to proceed based on the above, a discussion with RO developers SHOULD be made via the RO issue tracker or the OBO Community Slack using the #relation-ontology channel.

Note regarding property chains: If a proposed property chain makes use of relations that are themselves in RO, the property chain SHOULD be submitted to RO.

Examples

Counter-Examples

Criteria for Review

Each relation in the ontology that does not use an RO IRI will be checked to see if there is an exact label match in RO. If so, this will be flagged as an ERROR. Any other non-RO properties will be flagged with an INFO message.

This check is automatically validated.

Feedback and Discussion

To suggest revisions or begin a discussion pertaining to this principle, please create an issue on GitHub.

To suggest revisions or begin a discussion pertaining to the automated validation of this principle, please create an issue on GitHub.