Minimal requirement for term annotations in OBI (metadata)

This list represents the mandatory and optional metadata for representational units as agreed by the OBI coordinator committee. 
The proposed cardinalities are indicated in front of the name of the annotation property. Some are however still under discussion.

Mandatory metadata: MUST be provided

• 1: preferred_term: The concise, meaningful, and human-friendly name for a class or property preferred by the ontology developers. (US-English)
• 1: definition: The official OBI definition, explaining the meaning of a class or property. Shall be Aristotelian, formalized and normalized. Can be augmented with informal definitions to further explain the meaning of the term.
• 1,*: definition_editor: The name of the editor of the definition.
• 1: definition_source: An unambiguous and traceable reference to the source of the definition. Examples: ISBN, URI plus date, MeSH Term, PUBMED ID, DOI.
• 1,*: curation_status: The curation status of a class or property. The allowed values come from an enumerated list of predefined terms. Examples: raw import, obo definition incomplete, graph position temporary, uncurated, curation approved
• 1,*: example: A phrase describing how a term should be used. May also include other kinds of examples, such as widely known subclasses or instances of the class.

Optional metadata: SHOULD be provided

• 0,*: alternative_term: An alternative name for a class or property which means the same thing, i.e. semantically equivalent, as the preferred_term.
• 0,*: alternative_term_tag: A tag to indicate sets of alternative terms. Examples: toxicogenomics_community, abbreviation.
• 0,*: alternative_term_source: An unambiguous and traceable reference to the source of the alternative_term. Examples: ISBN, URI plus date, MeSH Term, PUBMED ID, DOI.
• 0,*: editor_note: An administrative note intended for the editor. It will not be included in the publication version of the ontology, so it should contain nothing necessary for end users to understand the ontology.
• 0,1: external_class: An annotation property that indicates external classes, including their subtrees, for a given anchor class.