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Hierarchy, Nested Instances of a Taxon:
Taxon concept encapsulation captures a taxonomic hierarchy
A taxon concept (broken circle) can be expressed as a set of instances (dots in the circle) with a name tag. For example, the family A is a taxon concept embracing the genera ( = instances), X, Y and Z. Instances of genus X are themselves lower level taxon concepts, i.e. species X a, X b and X c. This chain may be extended upwards as far as necessary, although its lower bound will be individual specimens. Each combination of a name and a taxon concept is specified in a publication, so not only taxon concepts but also the range of the hierarchy is publication dependent, enabling the database to hold multiple taxonomic views since each encapsulation is publication specific. Even if the publication does not specify all the hierarchy levels necessary to fill the levels between A and X, the data must reproduce this structure without adding missing levels. Gap-filling between them is a responsibility of the hierarchy navigator (if the user requires it to estimate the missing nodes), but each record should hold no data that are not in the publication. Scalability, by using the same data structure for any level of the classification, enables flexible handling of missing levels.
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