DELTA already allows dependencies between characters - such that if a specific state has been selected for a character, other characters are ignored (i.e. no wings, ignore anything to do with wings). Is there any other dependency relationships that might be required, or additional information about such a relationship?

Leigh brought this up; I would like to start a new thread with this. What problems do we have with dependency relationships (or integrity rules, to put it another way)?

Most of us are familiar with the dependency as implemented in DELTA compatible applications. here one character is defined as controlling, and that depending on which states is scored in a given item, other characters become applicable or inapplicable in that item. Questions:

1. Do we need both applicable and inapplicable definitions?

In DeltaAccess I assumed that applicable is the complement of inapplicable. If the complement of applicable states are defined as inapplicable, the application behaves the same way. This is only partly true.

a) If new states are added in the definition, some care is necessary. I realized that in DeltaAccess, but thought it the lesser problem. However, for the same reason for which we may need actually a "not" statement in the item description (a statement "color of X is NOT pure white" remains true, regardless of how many shades of beige are later added later on)

b) If multiple state are scored, the behavior needs to be defined. In the CSIRO programs, it seems that if two states are scored in a given item, a single one is sufficient to make another characters applicable or inapplicable (which makes sense, but is lost if the complement is choosen).

I have not found a good generalization for this, but loath to implement the rules in duplicate. Any ideas? This is certainly a question I am thinking about on the logical rather than conceptual level, but answering it may help to define the requirements, i.e. whether the DELTA applicable/inapplicable model should be followed, or whether alternative expressions are possible.

2. I recently had a good discussion with Wouter Addink and Flip Boer in Holland. Among other things we considered whether a structural hierarchy (leaf stalk is part of leaf is part of plant) could replace dependency rules. Clearly, it can replace some rules: if there is no leaf, all leaf characters will be inapplicable. However, it can not replace depencies based on multiple states that are not present/absence. Further, it may not always be true because we tend to use confusing terminology: Something at the leaf stalk base would belong to leaf stalk, but absence of leaf stalk (i.e. absence of measurable lenght of leaf stalk) does not imply absence of stalk based characters. Any further ideas on this?

3. (and finally): Does anybody have good examples where character _state_ dependencies would be necessary? This has been proposed for New Delta. I have no real objections, except that I have not found a good example where I would want to have it. ---------------------------------------------------------- Gregor Hagedorn G.Hagedorn@bba.de Institute for Plant Virology, Microbiology, and Biosafety Federal Research Center for Agriculture and Forestry (BBA) Koenigin-Luise-Str. 19 Tel: +49-30-8304-2220 14195 Berlin, Germany Fax: +49-30-8304-2203

Often wrong but never in doubt!