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First published 2002-10-17, last update: 2002-10-17.
TDWG working group: Structure of Descriptive Data (SDD)
(See also "Data challenge: Negative descriptive statements".)
Occasionally it is desirable to clarify the expression of a character by making explicitly negative statements. An example could be "red or yellow, but never orange" as shown in the data challenge above. The expression "but never" could be modeled as a "negating modifier". Examples of such modifiers are:
The modifier would have the special natural language property "suppress internal delimiter" set to override the normal and/or/comma rules of enumerating states in the natural language output. The system then needs special handling during queries or identification methods to exclude states that are scored with a negating modifier from the result set. This adds a significant additional burden on the implementation.
Furthermore, in the case where several states are explicitly negated ("but not A, B, or C") additional negating modifiers have to be introduced. These are difficult to represent in the user interface without special methods, since the comma and the or now have a negative meaning. Note also, that in an form-based user interface it would be logical to add rows of "and not A", "and not B", and "and not C", whereas the language expression applies Morgans rule under the assumption of an invisible bracket around the negation. The "And" therefore changes to "Or". Making this transparent to the user requires a significant effort by the application designer and training by the user.
An alternative to handle negating statements is to not provide form-based modifiers, and recommend that they are handled through reported notes. The data challenge statements would be expressed as:
It is proposed that SDD supports negating statements only through reported notes (= free form text).
Please send your criticism or suggestions to the SDD mailing list or to any of the authors.
Gregor Hagedorn; Vers. 1; 17. October 2002