test
node1
BFO:0000003
occurrent
node1->node1
node5
BFO:0000015
process
node1->node5
node2
GO:0008152
metabolic process
node3
GO:0006807
nitrogen compound
metabolic process
node2->node3
node4
GO:0097164
ammonium ion
metabolic process
node3->node4
node6
GO:0008150
biological_process
node5->node6
node6->node2
node7
BFO:0000001
entity
node7->node1