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

This is the VCAA sample ERD, published at ce/studies/infotech/it- applications/publications/IT-Apps- samp.pdf ce/studies/infotech/it- applications/publications/IT-Apps- samp.pdf

ENTITY

RELATIONSHIP

ENTITY ATTRIBUTE RELATIONSHIP

ENTITY ATTRIBUTE RELATIONSHIP KEY FIELD

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:

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 RELATIONSHIP KEY FIELD The answer

By Mark Kelly 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. VCE IT THEORY SLIDESHOWS