ertext transfer p roto col. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 6Infrastructure Issues
The
W eb:
CERN
and Tim Berners-Lee (among
thers);
1993
Nat. Centre fo r Sup ercomputer Applications' Mosaic;
Netscap
e commercial successo r then Microsoft IE.
Rememb
ers:
W
eb is not
nly
fo rm
f
hyp ertext system;
W
eb is not the same as the Internet...
Many
ther
ideas and mo dels:
T
ed Nelson's Xanadu transclusion ideas;
`The
Grid', E-Science
lots
f
hyp e... CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 7Usabilit y Issues: Accessibilit y
So
what do es distribution buy users?
Can
access remote resources:
computational
resources;
info
rmation resources;
human
resources (next lecture).
Tw
p
rinciple mo des
f
activit y:
b
ro wsing, undirected, ad ho c and
pp
rtunistic;
direct
sea rch, clea r task,
ften
time limited. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 8Usabilit y Issues: Bro wsing
As
designers, can y
u
attract user?
avoid
scrolling and gratuitous animation;
banner
advertising can b e
-putting;
high
do wnload latencies (see later).
Dw
ell time is a k ey issue:
examine
server logs fo r abandoned requests;
ma
y need remote usabilit y testing. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 9Usabilit y Issues: Directed Sea rch
T
ask directed interaction.
Action Specification Intentions Input devices
Interpretation Evaluation Interface display User Physical System Evaluation Bridge
Execution Bridge
Info
rmation retrieval: 1. F
rm
intention to nd info rmation; 2. T ranslate intention into query language; 3. Evaluate results
f
sea rch request; 4. If not found, refo rm intention
r
query ... CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 10Usabilit y Issues: Info rmation Saturation
Ma
y get a huge numb er
f
hits;
few
f
them ma y actually b e relevant to y
ur
task.
Sea
rch
n
D VD gives 6 million+ hits. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 11Usabilit y Issues: Info rmation Saturation
Precision:
number
f
r el ev ant hits total number
f
documents r etur ned
Recall:
number
f
r el ev ant hits total number
f
r el ev ant documents in col l ection
Relevance
feedback:
user
indicates which `hits' a re relevant;
system
uses this to imp rove next sea rch.
Rememb
er also the p roblem
f
sea rch IN a page. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 12Usabilit y Issues: Redundancy
Multiple
sources
f
info rmation:
if
ne
server fails then there a re
thers;
camera
b
ught
in Glasgo w but drivers in Singap
re.
Increase
in global comp etition:
B2B
(business to business) transactions;
if
y
ur
site fails I can nd another.
Usabilit
y is suddenly very imp
rtant.
2
click techniques (eg Amazon). CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 13Usabilit y Issues: Dela ys
Distributed
systems sp eed interaction: { cacheing holds info rmation close to p
int
f
use; { mirro r sites replicate a server close to user.
So
where do es a w eb page come from?
Alw
a ys try to minimise le sizes.
Avoid
gratuitous graphics and animations.
Give
users w a rning ab
ut
`exp ensive' resources.
Myth
f
the Innitely F ast Machine. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 14Usabilit y Issues: P
rtabilit
y and Java
P
rtabilit
y:
don't
just move data b et w een machines;
also
move co de and applications.
Lo
cal execution
f
remote co de:
Java
b yteco de do wnloaed from w eb;
Java
virtual machine executes
n
client;
securit
y issues?? CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 15Usabilit y Issues: P
rtabilit
y and Java
A
WT mak es interface lo
k
lik e host machine.
Swing
mak es interface lo
k
same
n
all machines. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 16Usabilit y Issues: Unp redictabilit y
Summa
ry:
don't
kno w where y
ur
info rmation is coming from;
don't
kno w where co de is b eing executed.
Loading
n
remote servers va ries:
with
time
f
the da y (US da ylight hours);
with
p ro cess p role (lots
f
computations?);
with
mirro r/cacheing supp
rt.
W
eb p erfo rmance is very unp redictable. CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 17Usabilit y Issues: Unp redictabilit y
Solutions
to unp redictabilit y .
Give
users an idea
f
the p
ssible
dela y:
indicate
le sizes fo r remote resources.
Indicate
qualit y
f
the resource:
thumb-nail
images
f
videos sho w p ro duction qualities.
Alternatively
, mak e all dela ys p redictable:
technically
not easy to do but some suggest adding dela ys;
everything
w
uld
tak e 5 minutes...
users
w
uld
develop c
ping
str ate gies;
slightly
w acky
not
sure... CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 18Usabilit y Issues: Securit y
Users
ften
don't kno w ab
ut
this.
Op
enly sha re passw
rds.
Use
the same passw
rd
everywhere 8(
So
cial issues
do
y
u
trust the w eb? CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 19Final Caveats
US
census 1990:
total
p
pulation
230,445,777;
198,600,798
nly
sp eak English;
31,844,979
p rima rily non-English sp eaking. V ery W ell W ell Not W ell Not at All 17,862,477 7,310,301 4,826,958 1,845,243 T able 1: 1990 US Census Data for Self-Rep
rted
Abilit y in English
US
census 2000:
54,000,000
(51%)
f
households had 1
r
mo re computers;
this
w as an increase
f
+42% from 1998.
US
census 2000:
45,000,000
(42%) use Internet at home;
it
w as 26% in 1998 and 18% in 1997.
Don't
get ca rried a w a y b y gro wth
f
Internet! CS-1Q: HCI (Lecture 5) c
C.W.
Johnson, 2001
SLIDE 20Summa ry
Infrastructure
issues:
Internet
p roto cols, the W eb and b ey
nd.
Usabilit
y issues.
Accessibilit
y .
Bro
wsing and task directed sea rch.
Info
rmation saturation and redundancy .
P
rtabilit
y , Java and RMI.
Dela
ys, unp redictabilit y and securit y . CS-1Q: HCI (Lecture 5) c
