In the past I have always made the relationship between two tables
using foriegn keys. So, to link employee to employer I would have a
column in employee table called employer_id so that one employee could
have one employer and one employer may have many employees. Pretty

I need help in understanding what is an automorphism of a database instance.
The following definition is from the book Relational Database Theory by
Atzeni and De Antonellis:
Definition: An automorphism of a database instance r is a partial function

can you help me please to analyse this situation and choose an appropriate
design  for that
The prloblem / Situation
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What are NULLs for?
Missing information? Then surely there should just be no tuple?
To indicate that there can be no value? Why not a seperate table with
a boolean value in the non-key column?

can you help me please to analyse this situation and choose an appropriate
design  for that
The prloblem / Situation
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I'm a newbie to dB programming.  I set up a set of tables (see below
after the RL signoff) to capture the relationship between a group of
people buying and selling stocks, and it worked well (using Visual
Basic Access for the front end). Now I want to extend this

Here's a website I stmbled across:
http://www.islandnet.com/~tmc/html/articles/datamodl.htm
Note that, at the start of the introduction,  the author says that analysis
is the most important part of any project.  That's rather different from the