Layered Architecture

                                                     Cross Section of Tiers

This cross section depicts 6 layers and a database at the bottom. However, it is still referred to as a 3-tier architecture. On the left the letters P, B, and D represent these 3 tiers: Presentation, Business, and Data tier respectively. Some of these tier consist of more than one layer which in the figure above is indicated by two letter acronyms: CL (Client Layer), PL (Presentation Layer), HL (Hosting Layer), SL (Service Layer), BL (Business Layer), and DL (Data Access Layer) respectively.