'A has_topic B' defines for the subject A, that it has the object B as its topic (A is in the scope of a topic B).
Subject A can be any concept or entity outside of an ontology (or an ontology concept in a role of an entity being semantically annotated). Object B can either be a concept that is a 'Topic', or in unexpected cases an entity outside of an ontology that is a 'Topic' or is in the role of a 'Topic'. In EDAM, only 'has_topic' is explicitly defined between EDAM concepts ('Operation' or 'Data' 'has_topic' 'Topic'). The inverse, 'is_topic_of', is not explicitly defined.