Re: General semantics

paul c wrote:
>> Have you read William Kent's /Data and Reality/ ?

Thanks for the pointer Bob, I just ordered it.

> Eg., I'd be curious as to who first talked about unary relations, which
> seem an essential part of Codd's breakthrough.

I don't know if I really understand what you're talking about, but a contribution from the realm of fact-oriented modeling might be helpful here. I'm not sure the ideas are analogous to what you mean by unary relations, but it's possible.

An "existential fact" is a fact that a certain thing exists.

For example "There is a city called Paris" contains an existential fact. Two in fact; the existence of the city and the existence of the city name 'Paris'.

There is also a binary fact which associates the two. Here, this fact is an instance of a binary fact type which might be described by the predicate "is called" having the two placeholders (also called roles) City and CityName, so the full "fact type reading" for this predicate is "City is called CityName".

A "unary fact type" is a fact type which contains a single placeholder. An example might be "Person smokes". Here Person is the placeholder, and smokes is the predicate.

It seems to me that the existential fact types (City, CityName, Person) are your domains. These are not unary fact types, they're existential fact types. The unary fact type "Person smokes" delineates a predicate which is either true or false for each Person (assuming CWA), and thus it delineates a subset of all actual Persons.

When you talk of a unary relation, do you really mean a set of unary facts of a single unary fact type? Or do you also include existential fact types under the term "unary relation"? Because for me, those are quite different things.

Clifford Heath, Data Constellation. Received on Thu May 20 2010 - 10:15:04 CEST