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

[Brad Ediger]

On Mar 23, 2007, at 1:03 PM, Sean Fulton wrote:

> 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.

If you want to get pedantic, the whole tuple would be a candidate  
key. A candidate key is only a primary key when it is singled out as  
such.

Back to our regularly scheduled programming...

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