www.entitymodelling.org - entity modelling introduced from first principles - relational database design theory and practice - dependent type theory
When the type of a part is identical to the type of the whole then the relationship must be looped around to renter the top after leaving the bottom: . This asserts that every type entity is composed of one or more type entities... each one of which, therefore, is itself composed of one more type entities ... and so on indefinitely.
The implied infinity in this model is a concern which is elaborated by Jonathon Swift for whom the type in question is the type flea:
In fact, if we are to avoid asserting an infinity of parts of parts of parts then we must specify zero, one or more parts within the whole as here: . Further, if we are to avoid asserting an infinity of ever bigger conglomerates as concerned Augustus De Morgan in his rejoinder:
The example in figure 7 illustrates this looping in action; it is further developed in subsequent sections.