Entity Modelling

www.entitymodelling.org - entity modelling introduced from first principles - relational database design theory and practice - dependent type theory

Scope Squares - A Warning

Not all relationship squares are scope squares. In the model of figure 22 the obvious square is not a scope square1. Instead the relationship stays in is global in scope i.e unconstrained. As such its scope square is as shown is figure 23.

Figure 22
The relationship stays-in is not constrained : a cast member stays in a hotel but this does not have to be in the same town that the performance is at.
Figure 23
The scope square for the unconstrained relationship stays in.

1Mathematicians would say that the diagram does not commute.