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3.1. Alias sets

There are several reasons why a user might want to collapse multiple kinds of birds into a single row in the generated report.

To complicate matters, the CBC database also includes records for hybrids (e.g., Cinnamon × Blue-winged teal) and species pairs (e.g., Hairy/Downy Woodpecker). In general, the CBC database represents kinds of birds as a triple (form, rel, alt_form). The form is a required six-letter code for the first or only kind of bird. For most records, rel is blank, but in the case of hybrids it is "x", and in the case of species pairs it is "/", and in these two cases the second kind of bird is encoded in the alt_form.

We define the term alias to mean a rule that all records for a given kind of bird should be combined with records for a different kind of bird.

In the most general form, an alias is a pair of (form, rel, alt_form) triples, such that any record matching the first triple is considered to be the same kind of bird as described by the second triple.

Here are some example aliases from an alias set for New Mexico records. The first translates Oldsquaw records to Long-tailed Duck. The second treats records for “Eastern/Western Screech-Owl” as Western Screech-Owl.

(("OLDSQU", " ", ""), (("LOTDUC", " ", ""))
(("EASOWL", "/", "WESOWL"), ("WESOWL", " ", ""))