---+++ Taxon Concepts
The term "taxon concept" reflects a recent focus in standards development within TDWG.  There has been a recognition that integration of biodiversity data will never be fully successful if we simply use taxon names as our only means to identify the intended taxa.  In general it will be useful if we can not only indicate which taxon name applies, but also which of the possible taxon concepts that may be associated with that name (i.e. which taxonomist's concept of the associated taxon applies).  This level of understanding may also help us to build better tools for mapping data shared under different taxon names, since many statements of synonymy relate not to the names but to a particular author's use of the names.  TDWG has been working on a data standard to support exchange of taxon names and/or taxon concept information (where such additional "taxon concept" information is available) - see http://www.soc.napier.ac.uk/tdwg/index.php.  In short this is equivalent to marking our use of taxon names with "sensu X" wherever appropriate.

A key example of where this may be useful is for ecologists who wish to compare e.g. vegetation surveys from different times, when different floras may have been used for recording.  These researchers want to be able to set up tools that will help them to map the taxa (taxon concepts) in use at one time onto those in use at another.

The reason that we are talking about assigning GUIDs to taxon concepts is that we need to be able to cross-reference between different taxonomists'
views of the taxonomy for each group.  Doing this with strings of the form "Genus species (Author, YEAR) sensu Author, YEAR" will never be reliable and robust.  There are significant issues in how we can manage identifiers for these concepts, but it is an important problem to address.

It could be that we need to focus on this problem in a different way - by making sure that we can unambiguously refer to taxon names and to publications.  Any taxon concept will then be identified by a pairing between the identifier for a publication and the identifier for a taxon referenced in that publication.