[Year 12 IT Apps] Exam ERD cardinality

[Mark KELLY]

Hi all

It seems from the sample exam's ERD that we don't need to indicate
cardinality (1:1, 1:many etc) in our ERDs.  If the exam decides to change
its mind about this and shows cardinality, that would be a - umphh -
cardinal sin.  <rimshot>

But seriously folks, without indications of cardinality, how can we get our
money's worth from an ERD.  Can one teacher supervise more than one class,
or can a subject be supervised by more than one teacher? Can a student
belong to more than one class? Can a class have many students?

One question: the sample ERD uses differences in shading as information
(e.g. of key fields). Is this conventional? I pity students if they ever
need to draw an entity with white text on black background in the exam.

And a dumb question: in which direction should the relationship between
entities be read? Logically, the teacher gives the mark to the student. But
read the other way, students give a mark to teachers.  Are relationships
commutative?

So many ERDs, so little red wine.

-- 
Mark Kelly
Manager of ICT, Reporting, IT Learning Area
McKinnon Secondary College
McKinnon Rd McKinnon 3204, Victoria, Australia
Direct line / Voicemail: +613 8520 9085, Fax +613 9578 9253
kel at mckinnonsc.vic.edu.au
VCE IT Lecture Notes: http://vceit.com
Moderator: IT Applications Edulist

All generalisations are false, except this one.
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