Illustration of the inconsistent phenotype grouping between successive levels. Each solid rectangle represents a phenotype node. A dashed line indicates combination operation. Phenotype groupings at level l and l+1 are inconsistent as the node BC at level l+1 is formed by breaking node AB and node CD at level l into two parts and combining one part of each node. In this case, the hierarchical structure cannot be represented as a tree.
Long et al. BMC Cell Biology 2007 8(Suppl 1):S3 doi:10.1186/1471-2121-8-S1-S3