I keep quoting John Arnold’s 2006 article “Security Services Model – Security Architectures”. His work can be read here:
https://docs.google.com/Doc?docid=0AexnQiysWyHGZGdwNWRiN2hfNTh2OHJoaGg&hl=en
I believe John’s thinking is essential to develop new direction in Security and Identity Management.