[postgis-users] Re: Dilemma: is gid really useful in a geoDB?
Sean Fulton
seanasy at gmail.com
Fri Mar 23 11:03:12 PDT 2007
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
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