schema {
  query: Query
}


type Query {
  dog: Dog
  cat: Cat
  alien: Alien
}

enum DogCommand {
  SIT
  DOWN
  HEEL
}

type Dog implements Pet {
  name: String!
  nickname: String
  barkVolume: Int
  doesKnowCommand(dogCommand: DogCommand!): Boolean!
  isHouseTrained(atOtherHomes: Boolean): Boolean!
  owner: Human
}

interface Sentient {
  name: String!
}

interface Pet {
  name: String!
}

type Alien implements Sentient {
  name: String!
  homePlanet: String
}

type Human implements Sentient {
  name: String!
  pets: [Pet!]
}

enum CatCommand {
  JUMP
}

type Cat implements Pet {
  name: String!
  nickname: String
  doesKnowCommand(catCommand: CatCommand!): Boolean!
  meowVolume: Int
}

union CatOrDog = Cat | Dog
union DogOrHuman = Dog | Human
union HumanOrAlien = Human | Alien