Room 2 of 10
From one thing to a kind of thing
Our question
Which distinctions help us describe Maria’s purchase?
Back at Harbor Coffee
Maria, Order #9821, and the physical Muffin #417 are particular instances. Person, Order, and Muffin are types or classes. Customer and Employee describe roles that Maria plays; they do not create two people.
An order’s accepted time is an attribute: a fact describing that order. We could identify every physical muffin, but the current waiting question may only need the product requested. The menu product and the prepared item are different things even when we choose not to track both.
Try a modeling decision
Which sketch preserves the distinctions?
Choose a view to see what it makes visible.
On the whiteboard
- Purpose → Which distinctions help us describe Maria’s purchase?
Read the worked explanation
Maria is an instance of Person. The same person can be Employee and Customer. Order #9821 is an instance of Order. Muffin #417 is a particular item; Muffin on the menu names a product kind.
Room not yet explored. Capstone progress is separate.
Inspect the source
Order #9821
Supplied recordsupportedOn September 15 at 10:15, Maria ordered a latte and a muffin.
Contents of one purchase. No waiting-time measurement was supplied.
One Maria, two roles
Participant accountsupportedMaria finished her shift at 10:00 and bought food at 10:15. It is the same person; Customer is her role in this purchase.
Employment and purchase in the fictional story.
Name the concept
Instance: One particular thing, such as Maria or Order #9821.
Type / class: A kind of thing whose instances share relevant meaning, such as Person or Order.
Role: How a person or thing participates in a context, such as Maria acting as a Customer.
Attribute / property: A descriptive fact attached to something, such as an order’s accepted time. It can become a separate thing when identity or history needs to be represented.