VCE IT Theory Slideshows - ITA By Mark Kelly [email protected] Vceit.com Entity Relationship Diagrams (ERD)
VCE IT Theory Slideshows - ITA
Feb 04, 2016
Entity Relationship Diagrams (ERD). VCE IT Theory Slideshows - ITA. By Mark Kelly [email protected] Vceit.com. This is the VCAA sample ERD, published at http://www.vcaa.vic.edu.au/vcaa/vce/studies/infotech/it-applications/publications/IT-Apps-samp.pdf. ENTITY. ENTITY. RELATIONSHIP. ENTITY. - PowerPoint PPT Presentation
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VCE IT Theory Slideshows - ITA
By Mark [email protected]
Vceit.com
Entity Relationship Diagrams(ERD)
This is the VCAA sample ERD,published at
http://www.vcaa.vic.edu.au/vcaa/vce/studies/infotech/it-applications/publications/IT-Apps-samp.pdf
ENTITY
ENTITY
RELATIONSHIP
ENTITY
ATTRIBUTE
RELATIONSHIP
ENTITY
ATTRIBUTE
RELATIONSHIPKEY FIELD
In the real world, primary field
names are often underlined.
In the real world, primary field
names are often underlined.
Reading the ERD
A Teacher
Reading the ERD
supervises
Reading the ERD
subjects
Reading the ERD
Each subject has a name attribute
Reading the ERD
The primary key for each
subject is the SubjectID field
Reading the ERD
A teacher also supervises
classes
Reading the ERD
Students belong to classes
But …
• The VCAA sample ERD has NO CARDINALITY• i.e.no indications of
– 1:1– 1:many– many:1– many:many relationships
We have to assume…
No cardinality is shown. Can one teacher supervise more than one subject or class?
We have to assume…
Can one subject or class be supervised by more than teacher?
This ERD does not say. Use the case study and common sense.
Unofficial additions…
The ‘many’ end of a relationship can be shown as “N” or “” …
N
1
Unofficial additions…
“Crow’s feet” notation of “many”
“Crow’s feet” notation of “1”
Optional Advanced Crowsfeet
If we wished to indicate that a school may enrol many students, or may not enrol any students at all. We also wish to indicate that each student attends exactly one school. This diagram indicates this optionality and cardinality:
SCHOOL
STUDENTEach school enrolls
at least zero
and at most many
students
Each student attends
at least one
and at most one
school
The VCAA sample exam question
List the three basic elements of entity relationship diagrams and provide an example of each from the diagram. (3 marks)
ENTITY
ATTRIBUTE
RELATIONSHIPKEY FIELD
The answer
By Mark [email protected]
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VCE IT THEORY SLIDESHOWS
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