On Wednesday 21 July 2004 14:58, Markus Bertheau wrote: > > 4) Replication: to identify an object of ANY type (record of any table > > regardless to datamodel), to store lists of deleted or modified objects > > (regardless to datamodel) > > That sounds like a datamodel on data that belongs to another data model,
that's right, these surr. keys actually belong to a metadata model, but it is also useful to references of a data model. and they are used this way. > > 5) Making a primary key: if there is no real key at all. > > When there's no key at all, there can't be a surrogate key, as I > understand it. In such cases a generated unique number comes in handy, > and it's a real primary key and no surrogate key. ...right. in case (5) we construct another datamodel indeed. with an artifichial real key :-) P.S. r u from Russia ? ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org