Fonte:
http://www.dgaiec.min-financas.pt/pt/destaques/op_economicos/NEWS_ecs_dss.htm
http://www.dgaiec.min-financas.pt/NR/rdonlyres/4AB6A61F-E6A3-49DD-8907-58363071F12C/0/Circular_n_99_2008_II.pdf