SDD Specifications Document

Robert A. (Bob) Morris ram at CS.UMB.EDU
Thu Mar 2 14:07:54 CET 2000

Leigh Dodds writes:
 > Date:         Thu, 2 Mar 2000 17:54:10 -0000
 > From: Leigh Dodds <ldodds at INGENTA.COM>
 > To: TDWG-SDD at
 > 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---

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

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