A toy example of a labeled poset. GO nodes are modeled by nodes with capital letters, with gene labels annotated to them in lower case. Note that the structure is neither a tree nor a lattice, but technically, the Hasse diagram of a poset P.
Verspoor et al. BMC Bioinformatics 2005 6(Suppl 1):S20 doi:10.1186/1471-2105-6-S1-S20