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# er diagrams and chen model

Posted on 2010-11-27
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Anyone have a good resource for learning how the chen model works in terms on relationship types.  Not sure when to use N or M,   when to use two lines,  etc

I also need to know of M:N is manay to many and is 1:N one to many

Looking for something that is easy to understand and has examples
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Question by:enigma1234567890
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Jeffrey Coachman earned 500 total points
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1. Well, Chen wrote an article on entity-relationship modeling, but this and the other related concepts (ex.: Normalization) were around way before then.

So the term "chen model" is just an attempt to reference this principle to a specific individual's famous work.

So just as "Boyce-Codd Normal form" is associated with Boyce and Codd, the same principles had existed prior to being "Named".

The same applies here for the "Chen Model"
*However* you must fully understand basic ERD, before you can begin to conceptualize the same things using "Chen Modeling"

2. <I also need to know of M:N is manay to many and is 1:N one to many>
Both of these statements are correct.
(Note that there is also 1:1, One To One)

3. Your original post states: "when to use two lines"
?
Can you be a bit more specific as to what you are trying to figure out.
(using a specific example)

If by "Two Lines" you mean as I have in the attached screenshot, ...then in terms of "Cardinality", this means: Mandatory Single
This is ERD Basic theory, and not specific to "Chen".
So again, you need to be familiar with Basic ERD theory and diagrams, then graduate to Chen.

;-)

JeffCoachman
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