DES501

Activity 4.1

Data modeling concepts, What are they? and why do we need them?

  • Entities – This is where the Data is stored, for example:
    • People
    • Products
    • Purchase
  • Attributes – This is information about that entity, another example:
    • People – Age, Gender, Name, Username, Contact details,
    • Product – Price, Quantity, Name, Manufacturer
    • Purchase – Date, Sum total
  • Descriptors – These are for, when attributes need requirements
    • Contact details are required
    • Username’s are Unique
    • Product name is also unique
  • Relationships – These connect the entities together
    • People places a purchase
    • Purchase is collects product
    • Product is sent to people
  • Cardinality – this explains the quantity/degree of the relationship between entities
    • This is shown through symbols on the lines
    • Example – One Person can Purchase many things
    • Here is a diagram of the Cardinalities and there meanings

crowsfoot

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