I've known for quite some time that better minds than mine have gone astray
in the attempt to overcome the object relational mismatch.  Just last week,
I ran across an article that outlines the O-R mapping problem better than I
ever could.

I have a situation that is somewhat the opposite of the case in which
you would use ON DELETE CASCADE on a foreign key in a child table to
ensure that when a row in the parent table was deleted, the delete
would cascade to the matching rows in the Child table (see example

Regarding so-called "union compatibility",.suppose relations A and B
with equal headings, say named h.  Suppose non-empty relation U with
only one attribute that is not in any other heading.
value i): A Join B projected on h, D&D style =

I am trying to get a top-down understanding of what an RDBMS does to
go
from a SQL Query to actual data (records served up).
Your thoughts / Links to good resources that cover this would be much

Suppose we have views u, w defined as relational expressions over base
tables x, y, z:
u = f(x,y,z)
w = g(x,y,z)

Not sure what to make of this:
USPTO Application #: 20080222602
Title: Declarative object identity using relation types
Abstract: The present invention provides a programming model based on

Why do implementation languages not allow this?  Surely not for logical
reasons?  We can delete from projection because NOT Pa implies NOT Pab,
eg., <NOT> R{a} -> <NOT> R{a,b}.  Logically, we can insert to
projections because Pab implies Pa.  Isn't the problem really a language

I had a though about possreps the other day, and I wanted to post
it, for no particular reason. This thought is not much developed,
so don't expect much. :-)
It occurred to me that possreps have a lot in common with union

Here's another kick at the old can.  The language 'delete D from J' is
usually taken to mean the facts represented by D are retracted to
produce a new value for J.  Expressed algebraically, the resulting value
is usually taken to equal J MINUS D, but this expression is not very