The statement · The vivid description · Element
The picture
A concrete description of the arrived state.
The part
What it is
Written in the present tense as though it had already happened, which is a device rather than a claim and works better than any other framing.
A few hundred words is enough. Longer and it becomes a document; shorter and it stays abstract.
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.