Re: Access as a RDBMS--why the multiple relationships?
Date: Sat, 15 Dec 2007 10:59:08 -0400
David Cressey wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message > news:4762f9cb$0$5297$9a566e8b_at_news.aliant.net... >
>>>OK, this is about my fifth day doing databases, and I've read about
>>>1NF, 2NF, 3NF here:
> > http://www.utexas.edu/its-archive/windows/database/datamodeling/rm/rm7.html, >>>>
>>>and I have a crappy book by a guy named Louis Davidson (APress), full
>>>of typos, bloated, and light on theory, but here's my question
>>>concerning Microsoft Access.
>>>I notice in Microsoft Access the relationship chart can, unlike most
>>>textbooks, have TWO, not just one, relationship arrows between
>>>tables. But I think (and I just want confirmation of this) that one
>>>of these two relationship arrows is bogus, and more like a query than
>>>a true relationship.
>>>relationship arrow one (sorry I can't do the SQL statement thing from
>>>my head, like some of you can, so I'll use prose instead):
>>>entity TABLE A has Primary Key PKA that migrates to entity TABLE B as
>>>a (manditory, and non-exclusive, but doesn't matter) Foreign Key FKB.
>>>In the "relationship diagram" (Access likes to use diagrams), this is
>>>properly shows as a 1 to infinity symbol, no problem, this is also in
>>>But I also using Access can set up ANOTHER SECOND?! relationship
>>>comprising a non-primary, non-key, non-unique field in TABLE A with a
>>>non-unique field in TABLE B. In the relationship diagram this shows
>>>up as "indeterminite" (no infinite or numbered symbols) and further
>>>you cannot check the box for "enforce referential integrity" because
>>>you get the error message (which makes sense) of "No unique index
>>>found for the referenced field of the primary table" (since the
>>>referenced field is not a primary key, or any kind of key).
>>>I just want confirmation that the SECOND relationship above is simply
>>>a bogus construct of Access, akin to a query constraint of some sort,
>>>and not really a 'relationship' as defined by RDBMS theory.
>>RDBMS doesn't really define 'relationship'. It's true Codd mentioned the
>>name in an early paper, but I doubt his use of the word in any way
>>resembles the crap that MSFT has been feeding you.
> > When Ray mentions the "Relationship Window", he's talking about a specific > tool that Access > offers the designer.
Yes, I assumed something like that. My response was to his statement "a 'relationship' as defined by RDBMS theory." If all he has it MSFT as an information source, he has no doubt been fed the bullshit ignorance that relational databases are named for referential integrity constraints.
That's a misconception MSFT promotes to sell shit to the unsuspecting, and it's a misconception that severely impedes learning.
The sooner he understands what relations are, the sooner he will develop a correct and empowered conceptual model of what is going on. Received on Sat Dec 15 2007 - 15:59:08 CET