Instrumentation · The joins · Element
The keys
What identifies a record across systems.
The part
What it is
A stable identifier that survives name changes, system migrations and the customer changing email address.
Where systems use different identifiers for the same entity, a mapping is required and is usually maintained by hand.
The smallest level
The attributes it carries
Each attribute is one of the framework’s shared types. What a date is, and how it is written, is defined once for the whole model — the note here says what it means in this particular place.