Basic 3 Tier Computing Model

• A server accepts input and produces output

  • A Web Server accepts HTTP request and returns a web page
  • a Database Server accepts a SQL request and returns records selected from database
  • An Object Broker accepts IIOP requests to invoke methods of an “object” (e.g. run a program)

• IIOP and HTTP are two common protocols (formats of control data) for inter program messages

• A Web browser (Netscape or Microsoft) can access any server at “the click of a button” with data from user refining action

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