Assume teachers, students, engineers, shoppers, salespersons, families teach, learn, collaborate, buy, sell, socialize via electronic versions of traditional human interactions combined with shared objects expressed in XML and rendered as web pages
Most sharing is asynchronous and one usually wishes to share synchronously same material that one accesses asynchronously
objects can be (electronic) text books, aircraft designs and simulations, expensive jewelry or photos of grandchildren
Only shared event model (used in Tango) of sharing (collaboration) is capable of necessary efficiency and customization to each user