Transitive Closure and 'pg_inherits'

Hi,

in case one use 'inherits' relationship to create a hierarchy of
tables, table 'pg_inherits' stores for each table the information of which
is its parent table.

During the evaluation of a query like
select * from Root;
where Root is the 'root' table of our hierarchy, postgreSQL needs to
find which tables are involved in the result (which tables belong to the
hierarchy).

My question is whether the way, in wich postgresql do this task, is a
transitive closure on table 'pg_inherits' or there is a better approach
implemented (like numbering scheme techniques etc.) ?

If there is a related url, please send it to me.