Fig. 2

a Excerpt of 13 concepts from the NCIt’s Biological Process hierarchy. Upward arrows represent IS-A relationships. Concepts with the same set of relationships are enclosed in a common, colored area. E.g., Cancer Cell Growth Regulation and Morphogenesis have one relationship Part of Process. Areas with the same number of relationships have the same color. E.g., the area {Location} and the area {Part of Process} are green. Area roots, e.g., Cellular Process, have bold outlines. b Area taxonomy for a, composed of five areas. Areas are represented by colored boxes labeled with their sets of relationships and numbers of concepts. They are organized in color-coded levels, according to number of relationships. The three concepts having the Location relationship are now represented by an area box named {Location}. Child-of links between areas are bold arrows; e.g., {Location, Part of Process} on Level 2 and {Location, Initiator BP, Part of Process} on Level 3 are child-of area {Location}