The window · The opening · Element
The cause
What opened it.
The part
What it is
Specific and dateable. “The market is growing” is not a cause; a regulation taking effect in March is.
The cause determines everything about the window, including how long it lasts and who else can see it.
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.