This system was designed originally to provide a nomenclatural infrastructure for data involving North American birds. It was specifically invented to handle Christmas Bird Count census data, but should have general application in other kinds of North American bird records work.
The system must cope with the continual changes to the reference taxonomy provided by the American Ornithologist's Union (AOU), allowing multiple taxonomic arrangements corresponding to the successive versions of The A.O.U. Check-list of North American Birds.
It must provide a way of sorting bird records into phylogenetic order, the traditional way of arranging bird taxa.
To satisfy this requirement, the system provides a taxonomic key number for each taxon in an arrangement. Sorting records on this key puts things in phylogenetic order.
It must support a system of short codes for bird names. The code system must be easy to learn and use. Codes must be short yet meaningful and easily translated back to names.