Number in Entity Modelling
Interpretation of Composition Relationships and Detail Free Entity Types
In viewing an entity model the lack of detail can be as significant as what is given.
In some context A if a composition leads to an entity type having no detail whatsoever,
other than its dependence on context A, then:
if the cardinality is Zero or One :
then the information content of x is that of a boolean indicator,
if the cardinality is Exactly One :
then x contains no information — the information content is zero
if the cardinality is Zero, One or More :
then the information content of x is that of a non-negative integer number.
Representations of Ordinal Number
There are three representations of ordinal number x associated with entity type A within an entity model.
As described above, as a composition relationship to a detail free entity that we
will name counter :
as a reference relationship x to a type representing the set of natural numbers and, say, denoted N
the standard representation — to say that x is an attribute of type number.