// element definitions
site((Category | Person)*)
Category(id, inclusion*, relate*)
  relate(categoryref)
  inclusion(Item)
    Item(id, open?, closed?)
      open(OpenAuction)
        OpenAuction(id, sell, bid*)
          sell(personref)
          bid(personref, stamp)
            stamp(date, time, increase)
      closed(ClosedAuction)
        ClosedAuction(id, buy, sell)
          buy(personref)
          sell(personref)
Person(id, interest*, watch*)
  interest(categoryref)
  watch(openauctionref)


// key constraints
KEY(Category.id)
KEY(Item.id)
KEY(OpenAuction.id)
KEY(ClosedAuction.id)
KEY(Person.id)

// foreign key constraints
KEYREF(OpenAuction.sell.personref --> Person.id)
KEYREF(bid.personref --> Person.id)
KEYREF(buy.personref --> Person.id)
KEYREF(ClosedAuction.sell.personref --> Person.id)
KEYREF(interest.categoryref --> Category.id)
KEYREF(watch.openauctionref --> OpenAuction.id)
KEYREF(relate.categoryref --> Category.id)