Hi Nico,
As a matter of clarification, perhaps also to the group -the "definition" I provided for a taxonomic concept has a bit of a normative quality (agenda is too grand a word). The thinking behind it is that concept taxonomy with fairly rapidly dissolve into name taxonomy if the distinction between acts of authoring (even if congruently), citing, and identifying to, concepts is not maintained with some consistency.
Agreed (I think...if I understand you correctly).
Sure, the Catalogue of Life (as just one example)purports to present some authoritative (mix of) taxonomic view(s). An informal name on a museum specimen by a late expert of the group probably translates into a concept in the mind of a student familiar with the group.
Yes, they're all implied concepts. It's just that only a tiny, tiny subset of them are well-defined.
I just think that there's this other taxonomy out therein the future, where we taxonomists think and act more like we care for others (incl. computers) to understand our classifications, where the parts come from, what's congruent and what has changed, how to precisely reconcile with previous views, etc. And for that future to become more real, perhaps a high threshold for identifying new concepts (in the sense of authoring anew [versus citing], not necessarily a new meaning) is needed.
Yes, I can see that (and we've had this conversation before). But first we need to come up with a common understanding of what a "taxon concept" is, and how to articulate it with some precision. One way to define a concept is as a clade; that is, something like "all descendents of the most recent common ancestor of these two organisms". This is one of the ways that Phylocode establishes the definition of a clade. It's not perfect (nothing is ever perfect), because with such definitions you will often have organisms that belong to two different taxon concepts simultaneously (hybridization, introgression, etc.) But that's not intrinsically a bad thing, as long as it's understood and accomodated. The real problem, of course, is that we're still in our relative infancy in our ability to discirn whether or not a paricular organism is, or is not, a descendant of the most recent common ancestor of two other organisms. Also, there is the problem of mapping to centuries of legacy information.
So I think the most practical way to define the cirumscription boundaries of a taxon cocnept at this point in history (and the one that is most likely to leverage historical content) is via type specimens (proxied by heterotypic synonyms). It's much fuzzier and less precise than the mechanism described in the previous paragraph, but far more practical.
What you're advocating is, I think, represents a reasonable path forward towards more robustly defined, and objectively articulated, taxon cocnepts.
In other contexts, possibly including the representationof identification events in museums, the bar for calling something a concept need not be that high (informal names, names outside of publications, local checklists, etc.). In any case, it's a matter of where one puts the emphasis, and hopefully I've pointed out where I would set it and why.
I think the key distinction that should be made is the distinction between a "defined" concept, and an "implied" concept. Almost every Taxon Name Usage (sensu lato) instance carries with it an implied taxon concept, but as I said, the vast, vast majority of those (especially if you include Museum specimen identifications) are extremely anemic on deails for understanding the boundaries of the implied taxon concept, and therefore it's difficult or impossible to reliably map the congurnecy (or not) with other implied or defined taxon concepts. On the other hand, what we should be really striving for is recognition of taxon concepts that are well "defined". These are also rooted in TNU's, but carry with them robust information for inferring the boundaries of the circumscribed concept (full synonymy, robust mateial examined, robust descriptions of morphological and/or genetic characters, etc.) I think this distinction is important to make ("defined", vs. merely "implied"), because what we'd ultimately like to do is find a way to map implied concepts to well-defined concepts.
Getting back to DwC, one area of direct relevance to this is the Identification class.
Most datasets out there simply slap a taxon name to a specimen or observation. Some of them go so far as to say who identified it to that name, and when. But most do not take the final step and anchor the identification to a particular well-defined concept (or, indeed, any TNU). All specimen identifications represent an action that places the specimen within the boundaries of a circumscribed taxon cocnept (whether the person making the identification realizes this or not). What we should be striving for is a mechanim to tie specimen identifications to particular TNUs that represent reasonably well-defined taxon cocnepts. The statement should be:
"On this date, this person asserted that this specimen falls within the taxon concept circumscription of Aus bus (L.) sec. Smith 1990".
If an Identification is a tuple of a Taxon instance (in the DWC sense) and an Occurrence instance (or an Individual instance, if that class becomes established), with associated metadata, then I think DwC is already primed to make the quoted statement above (i.e., to anchor Identifications to particular usage instances, because "taxonID" can represent a specific usage instance -- assuming the right attributes ae included). Retsated in DwC terms, this would be:
"On [dwc:dateIdentified], [dwc:identifiedBy] asserted that [dwc:occurenceID|dwc:individualID] falls within the taxon concept circumscription of [taxonID], which represents a taxon name usage for [dwc:scientificName] according to [dwc:nameAccordingToID]"
In the future, if Peter DeVries is successful with his ambitions, then this could be simplied to:
"On [dwc:dateIdentified], [dwc:identifiedBy] asserted that [dwc:occurenceID|dwc:individualID] falls within the taxon concept circumscription of [taxonID], which represents [dwc:taxonConceptID]"
Or maybe even:
"On [dwc:dateIdentified], [dwc:identifiedBy] asserted that [dwc:occurenceID|dwc:individualID] falls within the taxon concept circumscription of [taxonConceptID]"
In the latter two examples, taxonConceptID would represent an array or set of TNUs with congruent taxon concept definitions.
I'm still not 100% sure how best to use dwc:identificationReferences, other than perhaps as a method for aggregating multiple TNUs (assumed to refer to congruent, or at least overlapping concept circumscriptions), which were used by someone when making an identification.
Aloha, Rich