www.entitymodelling.org - entity modelling introduced from first principles - relational database design theory and practice - dependent type theory
The entirety of a modelling situation is represented by a half box at the upper edge of a diagram. Types whose entities may be free standing — not parts of or dependent on other entities are shown to be part of the entirety — which, relative to the situation, is the whole of everything.
The entirety is the absolute whole. It is a principle of logic that when we model we model a specific situation and this establishes an absolute. Fiction operates the same way as logic in this regard.
If the modelling situation is that of a single computer the entirety has cpu, drives and memory as parts as shown in figure 14 but if the entirety of the modelling situation is a network of computers then the whole has computers as parts which in turn each have drives and memory as shown in figure 15.
Similarly, the terms ‘true’ and ‘false’ are not relative terms — they do not rely on context for their interpretation — therefore they are absolutes and can be represented in relationship to the absolute. We will follow the computer science convention of representing them as being of type boolean which in common language might be translated as the made up word 'truthliness'. This leads to the model shown in figure 16 which depicts true and false as absolutes and as entities of type boolean. Note that from this model we are able to infer the only boolean entities are either the absolute true or the absolute false.
We might not have said this already: an entity model defines the rules by which entities of any of its types may exist; they do so by declaring the context for their existence i.e. other types of entities and the relationships in which they must be with these entities in order to exist. The model shown figure 11 in the previous section declares then that every noun phrase is either subject or object of a sentence1. Similarly, from the model in figure 16 we are able to infer that the only boolean entities are either the absolute true or the absolute false.