Diagram (#51)

## What's changed
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adding diagram and latest render of spec

## Change checklist
- [x] updated ontology, where necessary
- [x] updated shapes, where necessary
- [x] added or updated test cases, where necessary
- [x] any TODOs have been turned into trackable issues and referenced
where necessary

## Issue reference
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<!-- Fixes #{ISSUE}. -->
<!-- Resolves #{ISSUE}. -->