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From: dhartung@chinet.chi.il.us (Dan Hartung)
Newsgroups: comp.databases
Subject: Re: Relational Databases
Message-ID: <1991Jun07.063749.7904@chinet.chi.il.us>
Date: 7 Jun 91 06:37:49 GMT
References: <6822@vela.acs.oakland.edu>
Organization: Chinet - Chicago Public Access UNIX
Lines: 54

mebrenna@vela.acs.oakland.edu (Leonardo) writes:
>Does anyone have a good definition of a Relational Database, and a
>possible example?

Well, since E.F. Codd invented the concept, he gets to say what it is,
and here's something from his book "The Relational Model, Version 2" (1990):

"The relational model can be construed as a highly disciplined approach
to database management.  Adherence to this discipline by users is
enforced by the DBMS...."

Basically, a relational database is one that has been "normalized", that
is, taken through (at minimum) first, second, and third normal forms.
These "normal forms" are the processes of eliminating repeating data
in favor of index keys.

The three basic reasons for what is called "relational integrity" are:
  -- to keep related data together
  -- to eliminate redundancy
  -- to ensure that data is not lost during deletions

First Normal Form
1st normal form is the process of putting all repeating groups into
separate tables.  For instance, if you have an employee database,
with fields "Department" and "Manager", these should not be repeated
in each employee's record.  Instead, a key sould connect the employee
with a "Departments" file, where the manager's name is stored.

Second Normal Form
After achieving 1NF, one can cast a databse into second normal form.
This involves ensuring that every field in a table is dependent on
the primary key.  Thus, in an employee database, a "salary" field
might be dependent on "grade level" instead of who the employee is.

Third Normal Form
Each field must now be dependent only locally on its table key, not
by going through another database.  

Does any of that help?   :-)

>
>Thanks
>
>Michael E. Brennan                        | Office Automation, Software Support
>mebrenna@vela.acs.oakland.edu (Internet)  |   Phone 313-370-4561
>mebrennan@argo.acs.oakland.edu            |   Campus Network Support 
>michael@oasis.oa.oakland.edu (Novell)     |   Computer & Systems Engin
>                                          |     @Oakland University


-- 
Daniel A. Hartung           |  "What's the difference anyway, between being
dhartung@chinet.chi.il.us   |  safe and being rad, the joke's on us, we've
Birch Grove Software        |  all been had."  -- John Wesley Harding