Re: Sensible and NonsenSQL Aspects of the NoSQL Hoopla

On 04/09/2013 9:35 AM, Jan Hidders wrote:
> Codd explicitly referred to first-order logic in his work, so the link
> with Frege was clearly made. A reference to Tarski would have been nice,
> though. :-) The clear link notwithstanding, the relational model cannot
> be meaningfully described or thought of as a copy of FOL, either bad or
> good, since it has a very different purpose and makes entirely different
> claims about its purpose and utility. To confuse the two is
> misunderstanding entirely what database theory and database models are
> about.

To add to that, I like this quote from his 1979 paper which I think isn't controversial (unlike some other parts of that paper) and which I think makes it pretty clear that his model (or models if you like) is in part an application of FOL. If one agrees that it is indeed an application, that helps underline that it's not an alternative to FOL as well as not being some other things such as an implementation. I've re-paragraphed it to emphasize the last sentence of the first paragraph which I think is one of his most basic breakthroughs:

<quote ...
Suppose we think of a database initially as a set of formulas in first-order predicate logic. Further, each formula has no free variables and is in as atomic a form as possible (e.g, A & B would be replaced by the component formulas A, B). Now suppose that most of the formulas are simple assertions of the form Pub . - . z (where P is a predicate and a, b, . . . , z are constants), and that the number of distinct predicates in the database is few compared with the number of simple assertions. Such a database is usually called formatted, because the major part of it lends itself to rather regular structuring. One obvious way is to factor out the predicate common to a set of simple assertions and then treat the set as an instance of an n-ary relation and the predicate as the name of the relation.

A database so structured will then consist of two parts: a regular part consisting of a collection of time-varying relations of assorted degree (this is sometimes called the extension) and an irregular part consisting of predicate logic formulas that are relatively stable over time (this is sometimes called the intension, although it may not be what the logicians Russell and Whitehead originally intended by this word). One may also view the intension as a set of integrity constraints (i.e., conditions that define all of the allowable extensions) and thus decouple these notions from variability with time. ...
Whether the open or closed interpretation is adopted, the relational model is closely related to predicate logic. It is this closeness which accounts for the plethora of relational data sublanguages that are based on predicate logic.
... end quote> Received on Wed Sep 04 2013 - 21:37:21 CEST