Active Web Technology

Alan Dix

http://www.hiraeth.com/alan/topics/web/

alan@hcibook.com

user view

• 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