A LAN structure shows the structure of a kind of Local Area Network Is the symbol of a computer is the presentation part of the drawing Presentation represents a Big Computer represents a Computer represents a Small Computer FireWall represents a Firewall separating the presentation from the business logic Firewall is the connection between cpus and the firewall IS NOT a Mickey Mouse but rather an allegory of the working processes within the business logic Business Logic is the connection between the firewall and the engrenages Databases Legacy systems External applications Data is the connection between the engrenages and the Data components