Here's what I'm working with so far;

definition user {}

definition workspace {
  relation owner: user
  relation editor: user
  relation reader: user

  permission read: owner + editor + reader
  permission write: owner
}
 
definition project {
  relation workspace: workspace // Removed the namespace
  relation reader: user
  relation writer: user

  permission read: reader + writer + workspace->editor + workspace->owner
  permission write: writer + workspace->editor + workspace->owner
  permission invite_viewer: workspace->owner + workspace->editor
}