fun with referential integrity

[Ulf Wiger]

On Thu, 13 Mar 2003, Vladimir Sekissov wrote:

>Good day,
>
>etxuwig> .... or should I make it easier on myself and simply disallow
>etxuwig> cyclical dependencies? This seems like a fairly limiting
>etxuwig> restriction. How do the real pros do it? Does anyone know?
>
>For my opinion cyclical references are a bad thing. I
>usually model bidirectional relationships using another
>table D with composite primary key and foreign keys to B
>and C.

Reading "A Guide to the SQL Standard", by C.J. Date, notes
that "certain combinations of (1) referential structures
(...), (2)  referential action specifications, and (3)
actual data values in the database can together lead to
cetrain conflict situations and can potentially cause
unpredictable behaviour." It then moves on to explain that
these combinations are described elsewhere, and that it's up
to the DBMS to detect and disallow any dependencies that
would cause unpredictable behaviour. My interpretation is
that this must be done at runtime.

Unfortunately, the cited references are difficult to get for
free...

/Uffe
-- 
Ulf Wiger, Senior Specialist,
   / / /   Architecture & Design of Carrier-Class Software
  / / /    Strategic Product & System Management
 / / /     Ericsson AB, Connectivity and Control Nodes