Identity columns, was: Using long names

<Dave>
After that, a company number, customer number, item number, etc.,
might have the following constraint associated with it. This makes it a
"surrogate" key and can be changed without having to delete and re-add the
row.
</Dave>

An identity column is a surrogate key by definition! (surrogate key := A surrogate key (or synthetic key, entity identifier, system-generated key, database sequence number, factless key, technical key, or arbitrary unique identifier[citation needed]) in a database is a unique identifier for either an entity in the modeled world or an object in the database. The surrogate key is not derived from application data, unlike a natural (or business) key which is derived from application data.)

using surrogate keys normalisation is a little bit more easy, beacuse there are no dependencies of parts of a key. Another advantage might be stability of the key: there is no need to add another field to the key (example: one company buys another companie and a company id has to be added to the custumor number to bring the data in one table.
In this case an identity column could be a problem, if cganges to the custumor table are made in two diffrent systems on diffrent machines.

Changing a custumor number (as Rob mentioned) is not a good idea (IMHO), it's an identifier in the heads of people and in archives (paper or paperless).

D*B