Ok, but I'm gonna refute that and say that JDBC is not a tier  it's a
specification for developing drivers for communicating with the
database/persistence tier. Or by JDBC do you mean an overall data
access layer so your original list would look like:

1.Client Tier - Browser, Applet, Client Applications
2.Presentation Tier - Servlets, JSP
3.Business Tier - Business Objects (Session EJB, Business Classes)
4.Integration Tier - Data Access Layer (Entity EJB, JDO, SQL)
5.Backend Tier - Databases, JMS etc.