there's a few suites of views of the objects: ALL_TABLES, DBA_TABLES and USER_TABLES;

i try to stick with USER_tables, which are filtered to the schema you belong to (well the oracle user)

USER_TABLES is ~sys.tables

user_tab_columns is ~ sys.columns

here's an example i use when getting tables in a FK hierarchy order:

WITH MyCommonTableExpression

AS

(

SELECT

a.table_name as child_table,

b.table_name parent_table,

colb.column_name as child_column

from user_constraints a

INNER JOIN user_constraints b ON a.r_constraint_name = b.constraint_name

INNER JOIN user_cons_columns conb ON conb.constraint_name = b.constraint_name

INNER JOIN user_tab_columns colb ON colb.table_name = conb.table_name

AND colb.column_name = conb.column_name

WHERE a.constraint_type = 'R'

)

SELECT

parent_table,

child_table,

child_column,

1 as lvl

FROM MyCommonTableExpression

WHERE parent_table='GMACT'

START WITH parent_table = 'GMACT'

CONNECT BY PRIOR child_table = parent_table