logical: 
  - name: suppliers
    heading:
      - { name: sid,    domain: String,   mandatory: true }
      - { name: name,   domain: String,   mandatory: true }
      - { name: status, domain: Integer,  mandatory: true }
      - { name: city,   domain: String,   mandatory: true }
    constraints: 
      - { name: pk, type: primary_key, attributes: [ sid ] }
  - name: parts
    heading:
      - { name: pid,    domain: String,   mandatory: true }
      - { name: name,   domain: String,   mandatory: true }
      - { name: color,  domain: String,   mandatory: true }
      - { name: weight, domain: Float,    mandatory: true }
      - { name: city,   domain: String,   mandatory: true }
    constraints: 
      - { name: pk, type: primary_key, attributes: [ pid ] }
  - name: supplies
    heading:
      - { name: sid,    domain: String,   mandatory: true }
      - { name: pid,    domain: String,   mandatory: true }
      - { name: qty,    domain: Integer,  mandatory: true }
    constraints: 
      - { name: pk, type: primary_key, attributes: [ sid, pid ] }
      - { name: known_supplier, type: foreign_key, attributes: [ sid ], references: suppliers }
      - { name: known_part,     type: foreign_key, attributes: [ pid ], references: parts }