Descriptor: A descriptor determines what is "observed" and described on a specimen or a taxon. Example "Length of antennae", "inflorescence type", "Color of the wings". It means both (implicitly or explicitly) the organisme or part of it (antennae, legs etc..), and the quality on this part ("color, shape, counting ...). The title of a descriptor allows to formulate a "question" for a key ID: examples "What is the length of the antenna?" "What is inflorescence type?" "What is the color of the wings?"

State : A state is a value (or state character) linked to a descriptor. Example "yellow" for the descriptor "wings color", "5" for the descriptor "number of items of palps" etc..

Exception state : In the case of logical dependency between descriptors, the "parent's descriptor state" that make the "son's descriptors state" inapplicable is called an exception state for the son's descriptor.

Knowledge base : A knowledge base is a set of structured knowledge managed by a software and form a coherent and autonomous content.

Taxon : In taxonomy, a taxon is a conceptual entity that is supposed to group all living organisms with certain taxonomic common characteristics or diagnostic properly defined.