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• what changes?– media stream, presentation, content
• by whom?– automatic, site author, user– other users - feedthrough
• how often?– pace of change: days, months, seconds
computation
where does it happenclient
• applets, JavaScript, Shockwave, DHTML
server• CGI scripts, active server pages, servlets, etc,
other machine• authoring machine, database server, proxy
people• socio-techncal solutions
security
• for computation– code and data at same place!
• problem– data - needs to be secure– web-server - least secure machine– client machine even worse
… and networks!
architectural design
• what happens where
• affects:– complexity of implementation and maintenance– feedback
• seeing results of one’s own actions
– feedthrough• seeing effects of other people’s actions
client side dynamism
animation
Java and JavaScript
DHTML
animated gif or movie
•
• pros: simple
• cons: predetermined sequence
also … streaming audio/video
Java applet or JavaScript running locally
• pros: rapid feedback
• cons: only local, no feedthrough
aa
user's machine
(i)page loads
once
(ii)user interacts
locally
script/ J avarunning in client
web server
<H1>
The Act i ve Web
</ H1>
<p>
The web i s
changi ng,
i t s pages ar e
no l onger st at i c
server side dynamism
CGI scripts
searches
searches
• create indices off-line
• fast lookup when needed
see http://www.hcibook.com/
aa
web serveruser's machine
(ii)search results
rturned
(i)user fills
field in form
web page withtext field forsearchwords
I NDEX
CD- ROM 90 600 602CERN 156Cf A 524- 8CGI scr i pt s 603check boxes 129chess 44chunki ng 28- 9, 45
CGI scriptlooks upwords inindex
index filepre-computed
database access
client-side - JDBC
server side - CGI etc.
Java applet accesses database using JDBC
• pros: interactive DB access
• cons: bandwidth, security
webserver
user's machine
JD BCaccessesdatabase
J ava applet
CGI script accesses database
• pros: up-to-date, use existing DB
• cons: not proxy/index friendly
aa
web serveruser's machine
(ii) CGI scriptaccesses databaseusing SQL/ J DBC
<H1>
The Act i ve Web
</ H1>
<p>
The web i s
changi ng,
i t s pages ar e
no l onger st at i c
generatedpages
(i) requestto server
(iii)server returns
generatedpages
CGIscript
socio-technical solutions
off-line generation
people in the process
batch pre-generation of web pages
• pros: indexable, secure
• cons: slower turnaround
aa
third machineweb serveruser's machine
(ii) pages copiedto web server
via ftp
<H1>
The Act i ve Web
</ H1>
<p>
The web i s
changi ng,
i t s pages ar e
no l onger st at i c
generatedpages
(iii)server returns
generatedpages
(i) pages generatedoff-line from
database
<H1>The Act i ve Web</ H1><p>The web i schangi ng,i t s pages ar eno l onger st at i c