[Database class] Database ER model question

[Paul S. Wang]

Jack and db class,

It is a bad idea to have duplicated info in a database.  So
as long as info can be retrieved one way that is good enough.

Saving info multiple ways just mean that you need to update the info
in multiple places or you will end up with an inconsitent database.

Paul

On Wed, Feb 08, 2012 at 04:47:41PM -0500, Jack Selesky wrote:
> Date: Wed, 8 Feb 2012 16:47:41 -0500
> Subject: Database ER model question
> From: Jack Selesky <jselesk1 at kent.edu>
> To: pwang <pwang at cs.kent.edu>
> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (mscan1.vs.cs.kent.edu [131.123.37.140]); Wed, 08 Feb 2012 16:47:48 -0500 (EST)
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> 
> Hello Professor Wang,
> 
> Must all entity sets be connected to other sets via a relationship set? For
> example, consider  "officer" and "department" entity sets. officer will
> have attributes (officer_id, department_id, ... ) and department will have
> attributes (department_id, ...).  In order to find out in which department
> the officer is employed, all that is needed it to look up the officer's
> 'department_id' attribute.
> 
> Would it be necessary to have a "works_at" relationship set that connects
> the officer and department entity sets? If not, how can I represent the
> connection I explained above in an ER diagram? Thank you.

-- 
==============================================================================
 Paul S. Wang (王士弘)                      Email: pwang at cs.kent.edu            
 Dept. of Computer Science, Kent State U.   Tel: (330) 672-9051
 Kent, Ohio, USA 44242-0001                 http://www.cs.kent.edu/~pwang/ 
==============================================================================