Re: Examples of SQL anomalies?
Date: Mon, 30 Jun 2008 13:58:38 -0700 (PDT)
On Jun 29, 9:55 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "Rob" <rmpsf..._at_gmail.com> wrote in message
> > I am interested to see if anyone else finds any merit in the
> > relationship-oriented
> > approach.
> I think you've missed what underlies the Relational Model. If attributes
> from two different relations share the same domain and can share some of the
> same values from that domain, then there is an implicit relationship between
> those relations--in other words, if two relations can be joined on a common
> attribute or set of attributes, then there is already a relationship between
> those two relations. Referential constraints simply describe its character.
> Database schemata with some more complex referential constraints can be
> simplified--that is, replaced by a schemata that includes an additional
> junction relation and simpler referential constraints, but ultimately, the
> junction relation along with the simpler referential constraints boils down
> to just a more complex description of a single relationship. I just can't
> see any practical use for reifying descriptions of relationships.
How about the lattice relationships? Simplification?
Not using these in your current databases? Duh?
> On the fasttrack page you speak of breaking up the query processing for
> Query 3 into two separate queries and then evaluating them in sequence. If
> you can't see the problem with that, then perhaps you should go back to
> school. (Hint: Suppose an update by another user changes a row in A
> between the select into in Query 4 and the selecct in Query 5.) Just that
> causes me to question whether your idea merits consideration.- Hide quoted text -
You are correct. I thought I mentioned that:
"The scenario of both the logical data- and structure components residing in the same physical database corresponds to "Using Aggregate- exclusively in OLTP databases" (above). Without this co-location, referential integrity and therefore OLTP databases are not possible. However, for OLAP databases and analytic applications in general, the absence of referential integrity is not critical."
"In effect, we can construct a virtual OLAP database that spans multiple OLTP databases. All structure relations resides on a single server, entity relations reside anywhere. Entity updates are prohibited, structure updates are allowed. (If you allow entity updates, these are carried out remotely with no overarching transaction mechanism.) "
Before you criticize, perhaps you should read the whole page.
Rob Received on Mon Jun 30 2008 - 22:58:38 CEST