Re: Access as a RDBMS--why the multiple relationships?

David Cressey wrote:

> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:4762f9cb$0$5297$9a566e8b_at_news.aliant.net...
> 

> 
> 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.

>>>

>>>Here goes:

>>>

>>>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

>>>my textbook.

>>>

>>>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.

> 
> When Ray mentions the "Relationship Window",  he's talking about a specific
> tool that Access
> offers the designer.

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