<s>
A	O
PIGUI	B-Operating_System
(	O
Platform	B-Operating_System
Independent	I-Operating_System
Graphical	B-Application
User	I-Application
Interface	I-Application
)	O
package	O
is	O
a	O
software	B-Library
library	I-Library
that	O
a	O
programmer	B-Application
uses	O
to	O
produce	O
GUI	B-Application
code	O
for	O
multiple	O
computer	B-Device
platforms	I-Device
.	O
</s>
<s>
The	O
package	O
presents	O
subroutines	O
and/or	O
objects	O
(	O
along	O
with	O
a	O
programming	O
approach	O
)	O
which	O
are	O
independent	O
of	O
the	O
GUIs	B-Application
that	O
the	O
programmer	B-Application
is	O
targeting	O
.	O
</s>
<s>
For	O
software	O
to	O
qualify	O
as	O
PIGUI	B-Operating_System
it	O
must	O
support	O
several	O
GUIs	B-Application
under	O
at	O
least	O
two	O
different	O
operating	B-General_Concept
systems	I-General_Concept
(	O
e.g.	O
</s>
<s>
just	O
supporting	O
OPEN	B-Operating_System
LOOK	I-Operating_System
and	O
X11	B-Operating_System
on	O
two	O
Unix	B-Application
boxes	I-Application
does	O
n't	O
count	O
)	O
.	O
</s>
<s>
The	O
package	O
does	O
not	O
necessarily	O
provide	O
any	O
additional	O
portability	B-Architecture
features	O
.	O
</s>
<s>
Native	O
look	B-Application
and	I-Application
feel	I-Application
is	O
a	O
desirable	O
feature	O
,	O
but	O
is	O
not	O
essential	O
for	O
PIGUIs	B-Operating_System
.	O
</s>
<s>
Using	O
a	O
PIGUI	B-Operating_System
has	O
limitations	O
,	O
such	O
as	O
the	O
PIGUI	B-Operating_System
only	O
deals	O
with	O
the	O
GUI	B-Application
aspects	O
of	O
the	O
program	O
so	O
the	O
programmer	B-Application
responsible	O
for	O
other	O
portability	B-Architecture
issues	I-Architecture
,	O
most	O
PIGUIs	B-Operating_System
slow	O
the	O
execution	B-General_Concept
of	O
the	O
resulting	O
code	O
,	O
and	O
programmers	B-Application
are	O
largely	O
limited	O
to	O
the	O
feature	O
set	O
provided	O
by	O
the	O
PIGUI	B-Operating_System
.	O
</s>
<s>
Dependence	O
on	O
a	O
PIGUI	B-Operating_System
can	O
lead	O
to	O
project	O
difficulties	O
since	O
fewer	O
people	O
know	O
how	O
to	O
code	O
any	O
specific	O
PIGUI	B-Operating_System
than	O
do	O
a	O
platform-specific	O
GUI	B-Application
,	O
limiting	O
the	O
number	O
of	O
people	O
who	O
can	O
give	O
advanced	O
help	O
,	O
and	O
if	O
the	O
vendor	O
goes	O
out	O
of	O
business	O
there	O
may	O
be	O
no	O
further	O
support	O
,	O
including	O
future	O
OS	O
enhancements	O
,	O
though	O
availability	O
of	O
source	O
code	O
can	O
ease	O
but	O
not	O
eliminate	O
this	O
problem	O
.	O
</s>
<s>
Also	O
,	O
bugs	B-Error_Name
in	O
any	O
package	O
,	O
including	O
the	O
PIGUI	B-Operating_System
,	O
filter	O
down	O
to	O
production	O
code	O
.	O
</s>
<s>
Web	B-Application
browsers	I-Application
offer	O
a	O
convenient	O
alternative	O
for	O
many	O
applications	O
.	O
</s>
<s>
Web	B-Application
browsers	I-Application
utilize	O
HTML	B-Language
as	O
a	O
presentation	O
layer	O
for	O
applications	O
hosted	O
on	O
a	O
central	O
server	B-Application
,	O
and	O
web	B-Application
browsers	I-Application
are	O
available	O
for	O
pretty	O
much	O
every	O
platform	O
.	O
</s>
<s>
However	O
,	O
some	O
applications	O
do	O
not	O
lend	O
themselves	O
well	O
to	O
the	O
web	O
paradigm	O
,	O
requiring	O
a	O
local	O
application	O
with	O
GUI	B-Application
capabilities	O
.	O
</s>
<s>
Where	O
such	O
applications	O
must	O
support	O
multiple	B-Operating_System
platforms	I-Operating_System
,	O
PIGUI	B-Operating_System
can	O
be	O
more	O
appropriate	O
.	O
</s>
<s>
Instead	O
of	O
using	O
a	O
PIGUI	B-Operating_System
,	O
developers	B-Application
could	O
partition	O
their	O
applications	O
into	O
GUI	B-Application
and	O
non-GUI	O
objects	O
,	O
and	O
implement	O
the	O
GUI	B-Application
objects	O
in	O
the	O
native	O
API	B-General_Concept
.	O
</s>
<s>
Then	O
,	O
when	O
porting	O
,	O
only	O
the	O
GUI	B-Application
objects	O
need	O
to	O
be	O
rewritten	O
for	O
the	O
new	O
platform	O
.	O
</s>
<s>
There	O
are	O
some	O
software	B-Application
developers	I-Application
who	O
recommend	O
this	O
course	O
of	O
action	O
,	O
as	O
it	O
produces	O
a	O
better	O
fit	O
on	O
each	O
platform	O
and	O
eliminates	O
the	O
overhead	O
often	O
associated	O
with	O
PIGUI	B-Operating_System
toolkits	O
.	O
</s>
<s>
It	O
also	O
means	O
learning	O
how	O
to	O
code	O
for	O
every	O
target	O
platform	O
,	O
which	O
is	O
not	O
(	O
usually	O
)	O
a	O
trivial	O
task	O
,	O
hence	O
the	O
market	O
for	O
PIGUI	B-Operating_System
packages	I-Operating_System
.	O
</s>
<s>
Most	O
,	O
if	O
not	O
all	O
,	O
PIGUI	B-Operating_System
packages	I-Operating_System
take	O
one	O
of	O
three	O
approaches	O
to	O
providing	O
platform	B-Operating_System
independence	I-Operating_System
.	O
</s>
<s>
The	O
two	O
most	O
common	O
approaches	O
are	O
the	O
`layered	O
 '	O
and	O
the	O
`emulated	O
 '	O
user	O
interface	O
but	O
an	O
up-and-coming	O
approach	O
is	O
`API	O
emulated	O
 '	O
interface	O
.	O
</s>
<s>
Packages	O
using	O
a	O
layered	O
interface	O
access	O
native	O
,	O
third	O
party	O
,	O
GUI-building	O
toolkits	O
to	O
provide	O
the	O
look-and-feel	B-Application
compliance	O
for	O
each	O
particular	O
GUI	B-Application
.	O
</s>
<s>
Layered	O
user	O
interfaces	O
have	O
the	O
advantage	O
that	O
,	O
since	O
they	O
depend	O
on	O
other	O
products	O
which	O
concentrate	O
on	O
a	O
single	O
GUI	B-Application
,	O
they	O
have	O
to	O
provide	O
less	O
software	O
(	O
and	O
,	O
hence	O
,	O
are	O
usually	O
less	O
expensive	O
)	O
than	O
emulated	O
interfaces	O
.	O
</s>
<s>
Layered	O
interfaces	O
are	O
also	O
more	O
likely	O
to	O
get	O
the	O
native	O
look-and-feel	B-Application
correct	O
on	O
all	O
platforms	B-Device
.	O
</s>
<s>
In	O
an	O
emulated	O
user	O
interface	O
,	O
the	O
PIGUI	B-Operating_System
's	O
resultant	O
code	O
produces	O
low-level	O
calls	O
and	O
all	O
the	O
look-and-feel	B-Application
compliance	O
is	O
handled	O
by	O
the	O
PIGUI	B-Operating_System
software	O
itself	O
(	O
e.g.	O
,	O
for	O
OpenWindows	O
support	O
,	O
the	O
software	O
would	O
NOT	O
produce	O
an	O
XView	B-Library
program	O
that	O
must	O
be	O
compiled	O
with	O
the	O
XView	B-Library
toolkit	O
;	O
the	O
software	O
would	O
produce	O
code	O
that	O
interfaces	O
directly	O
with	O
X	B-Operating_System
intrinsics	O
)	O
.	O
</s>
<s>
To	O
provide	O
an	O
emulated	O
user	O
interface	O
,	O
a	O
package	O
provider	O
has	O
to	O
develop	O
a	O
lot	O
of	O
extra	O
code	O
for	O
look-and-feel	B-Application
support	O
.	O
</s>
<s>
Emulated	O
user	O
interfaces	O
have	O
the	O
advantage	O
that	O
someone	O
on	O
a	O
X11	B-Operating_System
workstation	O
,	O
for	O
example	O
,	O
can	O
see	O
how	O
the	O
Macintosh-style	O
UI	O
will	O
look	O
(	O
since	O
the	O
look-and-feel	B-Application
is	O
part	O
of	O
the	O
product	O
)	O
.	O
</s>
<s>
Emulated	O
interfaces	O
have	O
the	O
opportunity	O
to	O
provide	O
a	O
faster	O
GUI	B-Application
than	O
does	O
a	O
layered	O
interface	O
;	O
in	O
addition	O
,	O
it	O
does	O
not	O
require	O
purchase	O
of	O
(	O
or	O
learn	O
how	O
to	O
use	O
)	O
other	O
packages	O
to	O
build	O
GUI	B-Application
software	O
.	O
</s>
<s>
A	O
third	O
approach	O
to	O
platform	B-Operating_System
independence	I-Operating_System
is	O
emulating	O
one	O
of	O
the	O
supported	O
target	O
's	O
APIs	B-General_Concept
(	O
usually	O
,	O
the	O
Microsoft	O
Windows	O
API	B-General_Concept
)	O
to	O
target	O
other	O
GUIs	B-Application
.	O
</s>
<s>
With	O
one	O
of	O
these	O
products	O
,	O
one	O
would	O
program	O
using	O
the	O
emulated	O
API	B-General_Concept
and	O
the	O
code	O
would	O
be	O
(	O
to	O
the	O
extent	O
to	O
which	O
the	O
product	O
provides	O
portability	B-Architecture
)	O
portable	O
to	O
other	O
GUIs	B-Application
.	O
</s>
<s>
PIGUI	B-Operating_System
packages	I-Operating_System
are	O
pretty	O
similar	O
in	O
their	O
basic	O
functionality	O
;	O
they	O
each	O
provide	O
subroutines	O
or	O
objects	O
that	O
allow	O
the	O
user	O
to	O
build	O
windows	O
,	O
buttons	O
(	O
regular	O
as	O
well	O
as	O
radio	O
buttons	O
and	O
check	O
boxes	O
)	O
,	O
menus	O
,	O
and	O
the	O
like	O
.	O
</s>
<s>
support	O
for	O
the	O
platforms	B-Device
needed	O
,	O
</s>
<s>
the	O
approach	O
to	O
platform	B-Operating_System
independence	I-Operating_System
,	O
</s>
