Multi-tenancy presents lots of challenges for developers, but Gut Naor presents a real case using ruby on rails.  The concept is simple; namespaces,  it sounds easy but real name spaces are only available in a limited number databases.   MSSQL for example can do this, but doing so breaks the security model! Other BLOGS describe way to achieve a similar effect with mysql, but to really get a result you need to look at a db that stretches the envelope. For open-source  Postgresql hits the mark,ut side of open source the option is Oracle.

• Guy Naor’s presantation @ acts_as_conference 2009