Figure 1.

DAG vs Euler diagram representation: Non-trivial set relations. Comparison of a directed acylic graph (DAG) representation (left diagram) and an area-proportional Euler diagram visualization (right diagram) of the same set family. From the (hypothetical) Gene Ontology DAG on the left side the following set relations can be inferred: C ⊆ A, D ⊆ B, E ⊆ B, F ⊆ D, F ⊆ E, and D ∩ E ≠ ∅ since the two nodes have at least the elements of F in common. The Euler diagram representation reveals, in addition to the approximate visualization of the set cardinalities, further set relations (A ∩ B ≠ ∅, C ∩ B = ∅, D ∩ A ≠ ∅, E ∩ A = ∅, and F ∩ A = ∅) that are not specified in the DAG representation.