The ECCAIRS 4 descriptive factors are based on ICAO's ADREP 2000 taxonomy. They have been organised at five hierarchical levels. An event can be defined at each desired level. For each element three descriptions are given: detailed description (the complete name of the element), short description (the name of the element as to be presented on screen or in the reports, normally in the context of the section and with a limited length) and finally explanation (the formal definition/explanation of the element including references to where it has been defined etc.)