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

[Brent Wood]

--- Marc Compte <mcompte at sigte.udg.es> wrote:

> Hi,
> 
> Ermm ... wasn't one of Codd's rules "Each and every datum (atomic value) 
> in a relational data base is guaranteed to be logically accessible by 
> resorting to a combination of table name, primary key value and column 
> name."?

Yep.

> I find it surprising to see that "there's no need for a gid, from the 
> database point of view" and that primary keys are only needed because 
> "most applications want some way of identifying specific rows", as the 
> very core definition of the relational model clearly identifies this as 
> a crucial part of the model. Wanting to identify specific rows is not an 
> application oddity, it's part of the very definition of the model.


I think you are confusing an automatically generated gid attribute with a
primary key. Sure, it could be a primary key, but there may well be others,
which may be data driven (single or composite).

Making the gid optional, simply allows the user to use a gid if appropriate, or
lets them use an alternative primary key. If the table already has a primary
key, there is indeed "no need for a gid".

Just like Postgres itself now has optional oids. 

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)

Cheers,

  Brent Wood