[Informatics] ERD policy

Mon Apr 18 14:16:11 AEST 2016

I found this short Youtube video really helped!

https://www.youtube.com/watch?v=c0_9Y8QAstg

Roger Sidhom

From: ATKINSON-BUCK, Damien [mailto:Damien.ATKINSON-BUCK at ivanhoe.com.au]
Sent: Monday, 18 April 2016 12:36 PM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: Re: [Informatics] ERD policy

Hi Lucas,
I think the N is a reference to the N used in mathematics when looking at the cardinality of sets of numbers https://en.wikipedia.org/wiki/Cardinal_number and https://en.wikipedia.org/wiki/Aleph_number
Not sure when databases started using M as an additional letter to represent many, except to suggest that maybe it is was to avoid confusion of both tables requiring the same number of records by having the same letter linked to it?
Cheers
Damien

Damien Atkinson-Buck
Head of Learning Area: Technology/Arts
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From: Garth, Lucas A [mailto:garth.lucas.a at edumail.vic.gov.au]
Sent: Monday, 18 April 2016 12:07 PM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: Re: [Informatics] ERD policy

Hi Natalie & Mark

Seems no one knows what is going on. I’ve drummed into my students that one to many is 1:N despite how illogical it looks.

I’d have been fine for one to many to be 1:M and many to many to have M:M or even M:N.  But the research books I’ve seen use 1:N.

I imagine N stands for “a number of records” rather than many records.  (Then why don’t we use N:N?)

In the end all we want is consistency and I’m not sure the document provides this.  Page 3 needs to change the top diagram to be 1:M to ensure all of the diagrams are consistent.

Maybe it’s best to just always use crows feet and be done with it.

Lucas

From: informatics-bounces at edulists.com.au<mailto:informatics-bounces at edulists.com.au> [mailto:informatics-bounces at edulists.com.au] On Behalf Of Heath, Natalie
Sent: Monday, 18 April 2016 11:35 AM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: Re: [Informatics] ERD policy

Thanks Mark. I wish I’d had this when I was actually teaching it…. Last term….

Quick question. On page 3 the sample has 1:N library member borrows book…. Shouldn’t this be 1:M? Or am I missing something? 1:N isn’t in the list above it so I’m nicely confused.

Natalie

Mrs Natalie Heath
ICT Learning Coordinator

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From: informatics-bounces at edulists.com.au<mailto:informatics-bounces at edulists.com.au> [mailto:informatics-bounces at edulists.com.au] On Behalf Of Mark
Sent: Monday, 18 April 2016 11:12 AM
To: Year 12 VCE Informatics Teachers' Mailing List
Subject: [Informatics] ERD policy

Hi folks. The long-awaited VCAA Entity Relationship Diagram policy<http://www.vcaa.vic.edu.au/Documents/vce/computing/Informatics_examination_ER_Conventions.docx> is out.

And it includes cardinality with both Chen "1/M/N" and crowsfeet notations!

Finally!

--

Mark Kelly

mark at vceit.com<mailto:mark at vceit.com>
http://vceit.com

Natalie Heath
Marcellin Staff
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