Re: More on identifiers
Date: Sat, 06 Jun 2009 11:46:46 GMT
"David BL" <davidbl_at_iinet.net.au> wrote in message
> Informally I think of abstract identifiers as "internal glue" within a
> relational database. A bit more formally, they are characterised as
> identifiers that could be mapped bijectively to different values
> throughout the database without changing the recorded information.
> One would therefore hope that they aren't visible to end users.
> Due to the projection, all the abstract identifiers have disappeared
> from every relation. In a way, it's like seeing a database within a
> database! The value of the "inner" database records all the facts in
> the /context/ of just one of the items, and therefore has no need for
> abstract identifiers to glue things together.
> Flattening of DVAs requires introduction of abstract identifiers that
> are internal to the database, and can perhaps be seen as an
> implementation technique to map existing DBMS implementations of the
> flat relational model to a nested version that supports DVAs.
Are we going down this same road again? Received on Sat Jun 06 2009 - 13:46:46 CEST