Taxonomic concepts (sensu Berendsohn) embody the underlying meanings of scientific names as stated in a particular publication, thus offering a new way to resolve semantic ambiguities that result from multiple revisions of a taxonomic name. This paper presents a comprehensive and powerful language for representing the relationships among taxonomic concepts. The language features terms and symbols for concept relationships within a single taxonomic hierarchy, or between two related but

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... tly published hierarchies. Taxonomic concepts pertaining to a single hierarchy are characterised by parent/child relationships, whereas those pertaining to two independent hierarchies may have the following basic relationships: congruence, inclusion (non-symmetrical, relative to the side of comparison), overlap, and exclusion. The relationships are asserted by specialists who have the option to add or subtract concepts on one or both sides of a relationship equation in order to reconcile differences between non-congruent taxonomic perspectives. The terms 'and', 'or' and 'not' are available, respectively, to connect multiple simultaneously or alternatively valid relationship assessments, or to explicitly negate the validity of a relationship. The language also permits the decomposition of a relationship according to the intensional (property referencing) and ostensive (member pointing) aspects of the compared taxonomic concepts. Adopting the concept relationship language will facilitate a more precise documentation of similarities and differences in multiple succeeding taxonomic perspectives, thereby preparing the stage for an ontology-based integration of taxonomic and related biological information.