Design Patterns

Client - Server Model

n-tier Architecture : Each tier provides a specific functionality and interacts with adjacent tiers through well defined interfaces.
Early web-apps were 2-tier client architectures. Server served mainly static web pages.
3 Tier Architecture : Most common : Presentation Tier, Application Tier, Data Tier
App Tier divided into : Business Logic Tier, Data Access Tier (insulates from specific DB)
Presentation Tier divided into : Client Side UI components, Server Side UI components that generate web pages.