1. The internet Zurich Water Game
ZWG3

2. Distributed multi-user models
Participants can be anywhere, provided that they have internet access
E.g. in their office
No duration restrictions
Can be involved while doing their ordinary work
Can implement private negotiations easily
But
Less motivation without face-to-face interaction
Technical difficulties less easy to solve
Requires internet access

3. Implementation options
Client-side
Needs to run on many differently configured PCs
Java, Javascript OR
Server side
All software runs on a central server
Server generates HTML pages dynamically
Client only needs a web browser

4. Server side implementation
Apache web server
Standard web server
PHP
Scripting language
All normal programming constructs
Basic object orientated features
Good interfaces to other software and libraries
Relational database
PostgreSQL
MySQL
TCP/IP or other inter-process communication to other models
All this is open source, free and available under the GNU licence

5. Examples Gone Fishing! Zurich Water Game 3 Test the technology
Competitive game
Simple rules
Extensible (robot fishers!)
Zurich Water Game 3

6. The server Program Apache Web PHP Server module HTML Data read/write
Page
request
HTML
Data
read/write
Web page
PostgreSQL
database

7. Sample PHP <?php function show_scale($val) {
/* display a bar to show value of $val */
$val=round($val);
if ($val > 10) $val = 10;
if ($val < 0 ) $val = 0;
$colour = ($val >= 5 ? 'grn' : 'red');
echo "<td><img SRC=\"images/bar-$colour-$val.jpg\"
ALT=\"Value=$val\"
width=104 height=14></td>\n"; }
?>

8. Interface between PHP and database
$n_msgs = 3;
/* get the last 3 public messages */
$query = new query("SELECT id, sender, recipient,
to_char(timesent, 'HH24:MI on DD Mon')
as senttime,
timeread, msg
FROM msgs
WHERE (recipient = 'All')
ORDER BY timesent DESC LIMIT $n_msgs");
display_msgs($query);
?>