Modeling Multitier System

hello everybody…

I’m not an expert with UML.

I’am only a student who wants develop his Tesis.

Mi question is:

I don’t have idea about how modeling 3-tier System with UML…

Can you give me some example: (or give me a document to download)…

I heard that In Use Case Diagrams I most separte “System Context” of “System Requests”… (I don