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First published 2002-11-10, last update: 2002-11-10.
TDWG working group: Structure of Descriptive Data (SDD)
DELTA supports an ITEM ABUNDANCES directive (= ItemAbundance attribute in DeltaAccess) that is intended to support the function of interactive identification or key building. LucID does not support a similar element (pers. comm. K. Thiele), but XPER also uses frequency of items in an area to guide identification (pers. comm. N. Bailly).
ITEM ABUNDANCES values have no semantic definition in DELTA, but are defined based on the results obtained in the CSIRO programs. From the DELTA user guide, 4.10 (1999): "This directive specifies the abundances or weights of the items. The interpretation of the abundances or weights depends on the program for which they are intended. Generally, items with high abundances or weights will be given emphasis in some way – for example, they tend to come out early in keys."
It is generally questionable, whether the most frequent species should appear first in a given key. Even in keys or interactive identification aimed at the general public the most frequent organisms will be rarely sought, since they are well known to experts and amateurs alike. Item abundances may be useful to put truly rare species more towards the end of the key. Everything else should probably be treated identically.
However, the handling of such information may differ depending on the solution sought. For example in the case of medical diseases, disease frequency may be very important (e. g. to minimize diagnostic cost) and is known with a great deal of precision.
The usefulness of a separate item abundance data element as implemented in DELTA strongly depends on the area scope of the project. As data sets become more global, item abundances become increasingly less useful. Item Abundances can be modeled more appropriately as a distribution character with a frequency modifier:
Character distribution:
Germany: frequently present
France: rarely present
UK: absent
Note that the SDD frequency model supports verbal statements with an associated frequency range as well as exact statements of measured frequency. This should provide for any functionality that can be expected from a separate ItemAbundance data element.
Support of ItemAbundance in the SDD model was rejected at the SDD meeting in Brazil (2002).
Please send your criticism or suggestions to the SDD mailing list or to the author.
Gregor Hagedorn; Vers. 1; 10. Nov. 2002