Re: Another view on analysis and ER

From: JOG <jog_at_cs.nott.ac.uk>
Date: Tue, 4 Dec 2007 12:04:31 -0800 (PST)
Message-ID: <58c47eeb-adf0-414a-a1f4-9077039bd7fd@l1g2000hsa.googlegroups.com>

Genuine question guys. From an E/R perspective (one of the good variants, that allows relationships to have attributes), if I'm faced with the following data.

Fred married Wilma in Bedrock.
Barney and Betty married in Paris.

How do I decide whether I am dealing with a marriage entity or a marriage relationship?

The literature I'm reading here is telling me that the choice is based on what 'things' are key to the business. If my business is concerned with people (tax collection say), 'marriage' is best modelled as a relationship, whereas if the marriages themselves are my focus (perhaps I run a church) then its probably better as an entity.

Have I made the right interpretation here, and is there general agreement here? I am much more comfortable seeing that some variants allow relationships to themselves have attributes, and that there is nothing sacred about choices between using relationships or entities, making it a design decision instead.

Thanks in advance, J. Received on Tue Dec 04 2007 - 14:04:31 CST