rdf_db:rdf_keys_in_literal

Realises various queries on the key-set:

all Unify Answer with an ordered list of all keys.
key(+Key) Succeeds if Key is a key in the map and unify Answer with the number of values associated with the key. This provides a fast test of existence without fetching the possibly large associated value set as with rdf_find_literal_map/3.
prefix(+Prefix) Unify Answer with an ordered set of all keys that have the given prefix. See section 3.1 for details on prefix matching. Prefix must be an atom. This call is intended for auto-completion in user interfaces.
ge(+Min) Unify Answer with all keys that are larger or equal to the integer Min.
le(+Max) Unify Answer with all keys that are smaller or equal to the integer Max.
between(+Min, +Max) Unify Answer with all keys between Min and Max (including).