Required files
arel/algebra/relations/relation
arel/algebra/relations/utilities/compound
arel/algebra/relations/utilities/nil
arel/algebra/relations/utilities/externalization
arel/algebra/relations/row
arel/algebra/relations/writes
arel/algebra/relations/operations/from
arel/algebra/relations/operations/group
arel/algebra/relations/operations/having
arel/algebra/relations/operations/join
arel/algebra/relations/operations/order
arel/algebra/relations/operations/project
arel/algebra/relations/operations/where
arel/algebra/relations/operations/skip
arel/algebra/relations/operations/take
arel/algebra/relations/operations/lock