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


"raylopez99" <raylopez99@xxxxxxxxx> wrote in message
news:07e02bdb-86fc-4c17-a52b-fc2dbeb52b69@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
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.

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.

RL

My 2 cents. In my experience, when you have more than one relationship among
tables you are really describing roles. For example: Professor tutors
Student and Professor advises Student, where tutor and advisor are roles.

Evan


.

Relevant Pages

  • Re: Access as a RDBMS--why the multiple relationships?
    ... I notice in Microsoft Access the relationship chart can, ... non-unique field in TABLE B. In the relationship diagram this shows ... referenced field is not a primary key, ... 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. ...
    (comp.databases.theory)
  • Re: Access as a RDBMS--why the multiple relationships?
    ... In the "relationship diagram", ... non-unique field in TABLE B. In the relationship diagram this shows ... referenced field is not a primary key, ...
    (comp.databases.theory)
  • Access as a RDBMS--why the multiple relationships?
    ... In the "relationship diagram", ... non-unique field in TABLE B. In the relationship diagram this shows ... referenced field is not a primary key, ...
    (comp.databases.theory)
  • Re: Access as a RDBMS--why the multiple relationships?
    ... In the "relationship diagram", ... non-unique field in TABLE B. In the relationship diagram this shows ... referenced field is not a primary key, ... Relational is not named for referential integrity. ...
    (comp.databases.theory)
  • Re: How to change the RowSource in a SubForm in VBA code
    ... It makes sense that the same problem situtions could arise when setting the subform's RecordSource on the fly. ... from the Database window onto another form or report or by using the ... Microsoft Access automatically sets the LinkChildFields ... primary key. ...
    (comp.databases.ms-access)