[postgis-users] Re: Dilemma: is gid really useful in a geoDB?

[Sean Fulton]

On 2007-02-22 13:05:29 -0500, Brent Wood <pcreso at pcreso.com> said:
> 
> Making these fields optional does NOT make primary keys optional. (well,
> they are, but the relational model is well & truly broken if you don't 
> have one,
> whether or not you actually define it as such. The data can have a viable
> primary key, even if it is not specified as such in the schema)

Strictly speaking, the relational model is broken when there are 
non-unique tuples. When all tuples are unique, you have a de facto 
primary key -- the whole tuple. Uniqueness is, I think, the only 
requirement. A primary key is a convenience that summarizes the 
uniqueness of a tuple. In the fourth normal form and higher they are 
unnecessary.

	Sean