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VCE IT Theory Slideshows - ITA

Entity Relationship Diagrams (ERD). VCE IT Theory Slideshows - ITA. By Mark Kelly mark@vceit.com 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.

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VCE IT Theory Slideshows - ITA

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  1. Entity Relationship Diagrams (ERD) VCE IT Theory Slideshows - ITA By Mark Kelly mark@vceit.com Vceit.com

  2. This is the VCAA sample ERD,published athttp://www.vcaa.vic.edu.au/vcaa/vce/studies/infotech/it-applications/publications/IT-Apps-samp.pdf

  3. ENTITY

  4. ENTITY RELATIONSHIP

  5. ENTITY RELATIONSHIP ATTRIBUTE

  6. ENTITY KEY FIELD RELATIONSHIP ATTRIBUTE

  7. In the real world, primary field names are often underlined.

  8. Reading the ERD A Teacher

  9. Reading the ERD supervises

  10. Reading the ERD subjects

  11. Reading the ERD Each subject has a name attribute

  12. Reading the ERD The primary key for each subject is the SubjectID field

  13. Reading the ERD A teacher also supervises classes

  14. Reading the ERD Students belong to classes

  15. But … • The VCAA sample ERD has NO CARDINALITY • i.e.no indications of • 1:1 • 1:many • many:1 • many:many relationships

  16. We have to assume… No cardinality is shown. Can one teacher supervise more than one subject or class?

  17. 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.

  18. Unofficial additions… The ‘many’ end of a relationship can be shown as “N” or “” … N  1

  19. Unofficial additions… “Crow’s feet” notation of “many” “Crow’s feet” notation of “1”

  20. 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:

  21. 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)

  22. The answer ENTITY KEY FIELD RELATIONSHIP ATTRIBUTE

  23. VCE IT THEORY SLIDESHOWS By Mark Kelly mark@vceit.com vceit.com These slideshows may be freely used, modified or distributed by teachers and students anywhere on the planet (but not elsewhere). They may NOT be sold. They must NOT be redistributed if you modify them.

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