[Informatics] ERD policy

Mon Apr 18 14:39:53 AEST 2016

A nice find, Roger.  Thanks.

On 18 April 2016 at 14:16, Roger SIDHOM <rsidhom at ozford.edu.au> wrote:

> 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
> <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
> <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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> Marcellin College
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>
> *From:* informatics-bounces at edulists.com.au [
> mailto:informatics-bounces at edulists.com.au
> <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
>
> http://vceit.com
>
>
>
> *Natalie Heath *
>
> Marcellin Staff
>
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> MARCELLIN COLLEGE
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-- 

Mark Kelly

mark at vceit.com
http://vceit.com
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