Ontological representation of zebrafish heart development. The ontological representation of heart development includes overlapping start and end stages where the start stage of a developing structure is the same as the end stage of the previous structure, and abutting, where a structure ends the stage before the start stage of the next structure. Overlapping and abutting start and end stage design considerations are illustrated: 1) start_stage and end_stage temporally overlap for ‘primitive heart tube’ (ZFA:0000149) end_stage ‘Pharyngula:Prim-5’ (ZFS:0000029) and ‘heart tube’ (ZFA:0000360) start_stage ‘Pharyngula:Prim-5’ (ZFS:0000029); 2) end and start stages abut for ‘heart tube’ (ZFA:0000360) end_stage ‘Pharyngula:Prim-25’ (ZFS:0000031) and ‘heart’ (ZFA:0000114) start_stage ‘Pharyngula:High-pec’ (ZFS:0000032). Note: several is_a parents omitted from the figure for clarity. Stage arrows indicate stage order not length.