Collaborative Learning through Flexible Web CVE - Teaching through Multi-User Virtual Environments - page 474

Figure 2. SEE in partnership with the Israel Museum in Jerusalem

in four different countries, involving nearly 1,500
students, have used the environment for highly
rewarding educational activities.
The technical problems below described re-
quired a different approach:

ones not interested to the message). It was
the job of every client to decide whether
to keep or to discard messages received
by the server. This approach resulted in a
too low refresh rate (position vectors re-
freshed every two seconds) of the shared
state scene; avatars were often visualized
as not moving continuously, but disappear-
ing here and reappearing there.
• Non-optimal reliability : as the MUS (Multi
User Server) did not provide any acknowl-
edgment of a received message, there was
no assurance that sent messages really ar-
rived at the server and from there to each
client application. This negatively affected
the overall consistency: avatars may have
different positions for different clients;
sometimes actions performed on a client
were not executed at all on another client;

• Lack of flexibility: : there was no modular-
ization of content or behavior; everything
had to be hard coded, within Director
stages (using cast objects coordinated with
Lingo); it was long and expensive to carry
on any modification.
• Non-optimal performances : the commu-
nication server (Macromedia Multiuser
Server) worked only as “stupid” message
dispatcher. Every client, which needed to
communicate with another client, had to
send data to this central server that for-
warded it to every other client (even the