directive @core(feature: String!) repeatable on SCHEMA

directive @join__owner(graph: join__Graph!) on OBJECT

directive @join__type(
    graph: join__Graph!
    key: String!
    resolvable: Boolean = true
) repeatable on OBJECT | INTERFACE

directive @join__field(
    graph: join__Graph
    requires: String
    provides: String
) on FIELD_DEFINITION

directive @join__graph(name: String!, url: String!) on ENUM_VALUE

enum join__Graph {
    A @join__graph(name: "a", url: "http://example.com/a")
    B @join__graph(name: "b", url: "http://example.com/b")
}

type Book implements Media
    @join__type(graph: A, key: "id")
{
    id: ID!
    reviews: [Review!]! @join__field(graph: B, requires: "title")
    title: String! @join__field(graph: A)
}

type Review {
    score: Int! @join__field(graph: B)
}

type Query {
    topRatedMedia: [Media!]! @join__field(graph: B)
}

interface Media
    @join__type(graph: A, key: "id")
    @join__type(graph: B, key: "id", isInterfaceObject: true)
{
    id: ID!
    reviews: [Review!]! @join__field(graph: B, requires: "title")
    title: String! @join__field(graph: A)
}