This is a core mapping class, all objects representing GraphQL objects and fields are instance of that object.
All instances of MUST be in the namespace prefix `gql: <http://www.openlinksw.com/schemas/graphql#>`.
Example: query { planet { order_num } } will use `gql:planet` and `gql:order_num` to find RDF class and property.
In RDF terms mappings should be defined as: `gql:planet gql:rdfClass ex:Planet` and `ex:planetOrder gql:field gql:order_num`.