A subset ontology that is designed for basic applications to continue to make certain simplifying assumptions; many of these simplifying assumptions were based on the initial version of the Gene Ontology, and have become enshrined in many popular and useful tools such as term enrichment tools. Examples of such assumptions include: traversing the ontology graph ignoring relationship types using a naive algorithm will not lead to cycles (i.e. the ontology is a DAG); every referenced term is declared in the ontology (i.e. there are no dangling clauses). An ontology is OBO Basic if and only if it has the following characteristics: DAG Unidirectional No Dangling Clauses Fully Asserted Fully Labeled No equivalence axioms Singly labeled edges No qualifier lists No disjointness axioms No owl-axioms header No imports