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Chen model vs Crow's foot model

Posted by trautw 
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trautw
Chen model vs Crow's foot model
July 31, 2006 10:58AM
Can we use either model in the exam or is the question going to request a specific format.

Thx,

Werner
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united
Re: Chen model vs Crow's foot model
July 31, 2006 08:37PM
You can use either model.
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johannes.joubert
Re: Chen model vs Crow's foot model
October 25, 2006 08:13AM
I am rather disappointed that little direction on both models are provided in the model answers of the assignments. If we chose to use the cf model, we cannot check it against the lecturers answers. Please provide both models in future!
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jeanbodemer
Re: Chen model vs Crow's foot model
October 25, 2006 10:34AM
I also think that the level of detail required for a crow model is much more than a Chen model. Just look at the solution of Assignment 1 question 3. How can 15 points be given for such a simple solution, they didn't even indicate attributes?

I had a comment on my solution to convert the relationship to a bridge entity, isn't benefit already a bridge entity? I drew it exactly like figure 4.26 in the text book but got marks deducted.
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jeanbodemer
Re: Chen model vs Crow's foot model
October 25, 2006 10:52AM
Here is a link to my solution, can anyone tell me what is wrong with it?

ER Diagram for Assignment 1 Question 3
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Carl
Re: Chen model vs Crow's foot model
October 25, 2006 11:05AM
You did not write in the relations, saying that JOB is assigned to an EMPLOYEE, an EMPLOYEE has BENIFITS
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jeanbodemer
Re: Chen model vs Crow's foot model
October 25, 2006 11:08AM
Carl Wrote:
-------------------------------------------------------
> You did not write in the relations, saying that
> JOB is assigned to an EMPLOYEE, an EMPLOYEE has
> BENIFITS

Oops, forgot about that.

But like I said, I also got a comment indicating that I should convert the plan -> benefit <- employee link to a bridge entity. Isn't it already one?
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Carl
Re: Chen model vs Crow's foot model
October 25, 2006 11:12AM
Not the way you showed it, you said the relationships are optional.
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jeanbodemer
Re: Chen model vs Crow's foot model
October 25, 2006 11:24AM
You're right, I looked at the question again and noticed that all plan's and employee's have at least one value in the benefit entity. (Personally I still think it should be optional as a plan might not be linked to a benefit and an employee might not have any benefits)

I still don't get the comment about the bridge entity though.
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jeanbodemer
Re: Chen model vs Crow's foot model
October 25, 2006 11:24AM
By the way, thanks for your help Carl.
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Carl
Re: Chen model vs Crow's foot model
October 25, 2006 11:32AM
Any time!
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vaughn
Re: Chen model vs Crow's foot model
October 25, 2006 03:47PM
How about the past exam

Do you guy know how to do 1b?
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tjvanaarde@web.de
Re: Chen model vs Crow's foot model
October 25, 2006 07:04PM
I think to show that benefit is a bridge entity you must put lines in the four corners of the box to make the corners look like triangle arrows pointing outward. A bridge entity and a composite entity is the same thing page 154 in the 2004 edition of the text book shows what i mean.
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jeanbodemer
Re: Chen model vs Crow's foot model
October 25, 2006 07:06PM
vaughn Wrote:
-------------------------------------------------------
> How about the past exam
>
> Do you guy know how to do 1b?

You have to ensure your ER diagram is in 3NF and then show the relations as in assignment 2 (question 1b and 2)

<<edited>>
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