Leigh Dodds writes:

Date: Thu, 2 Mar 2000 17:54:10 -0000 From: Leigh Dodds ldodds@INGENTA.COM To: TDWG-SDD@usobi.org Subject: Re: SDD Specifications Document

[...]

2. Collated Character source. I see these as essentially

a drill down mechanism that further identifies a 'bottom-level' taxon. Is it reasonable to include character dependencies 'upwards'? Am I right in believing that multiple character sets could drill down into the same source (perhaps produced by different organisations, researchers, techniques). In this case, is there a principal source for going back upwards? It seems unfair to expect a treatment to keep track of all other treatments which point to it (I may be infering too much here).

Not sure if I am misreading what you mean here, but if not, then I whine thusly:

A /single/ character set can get to the same taxon in different ways. Don't come up with something that guarantees that the key graph must be a tree. Even dichotomous keys aren't actually always trees even though when printed they often look so. They look so because humans routinely impute structure from format, which is one thing XML is supposed to help us avoid. Though you have to work to represent non-trees in XML...

In an arbitrary directed acyclic graph, if an application wants to know how it got from one node to another, it has to keep track of the path or else climb upwards along each parent looking for a determining character. The latter is an exponential strategy, but the size of key graphs may well be too small to bother worrying about that.

small -----------------speciesA / / / / / / ----wing spot--- / red--- \ / large --- wing color--- \ blue---speciesB

BTW, this hopefully not absurd example suggests how much easier it is to deal with sometimes---but not always---irrelevant characters using XML and its semi-structured generalizations than using table and matrix representations of character data.

Bob Morris