The _C_HLEVEL_ is the hierarchical level of the term. The term at the highest level of a hierarchy has a value of 0 and the next level has a value of 1 and so on.
The screen shots below show how the values in _C_HLEVEL_ determin the way ontology data looks in the user interface.

• The name of the ontology table is I2B2; the entry with C_HLEVEL 0 has C_NAME = "Ontology" and is the root of the ontology tree.
• The folders underneath Ontology all have C_HLEVEL = 1.
• When a user clicks on a plus sign ( ) to open a folder, the next level to open has the value C_HLEVEL = 2. Thus the field

Example 1: C_HLEVELS 0 and 1


Example 2: C_HLEVELS 0, 1, and 2