Discussion: Part/whole relations and ISO 15926-2

This page is intended for a particular example given in ISO 15926-2, page 102, where part/whole relations are discussed.

Of particular difficulty is the fact that the diagram illustrating the discussion seems to confuse the notion of entity type with that of a defined class or relationship. In particular, the name assembly of individual is given as the name of a relation, even though this also names one of the most important entity types for relations.

The following graph is intended as an attempted reconstruction of the mentioned graphic. More discussion will follow, in the hope that confusion can be laid to rest.


  • The other relationship instance should have an (additional) entity type assembly of individual
  • The relation which is called "assembly of individual" (overusing the name, clearly) should have an additional entity type class of assembly of individual
  • Perhaps the graph, as given in ISO 15926-2, is confusing only because the text is at the point in question only intending to make a point about assignment of cardinality constraints. Indeed, the section header is called precisely "Cardinality constraints".
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