<s>
Operational	B-Operating_System
transformation	I-Operating_System
(	O
OT	O
)	O
is	O
a	O
technology	O
for	O
supporting	O
a	O
range	O
of	O
collaboration	O
functionalities	O
in	O
advanced	O
collaborative	B-Application
software	I-Application
systems	O
.	O
</s>
<s>
OT	O
was	O
originally	O
invented	O
for	O
consistency	O
maintenance	O
and	O
concurrency	B-Operating_System
control	I-Operating_System
in	O
collaborative	O
editing	O
of	O
plain	O
text	O
documents	O
.	O
</s>
<s>
Its	O
capabilities	O
have	O
been	O
extended	O
and	O
its	O
applications	O
expanded	O
to	O
include	O
group	O
undo	O
,	O
locking	B-Operating_System
,	O
conflict	O
resolution	O
,	O
operation	O
notification	O
and	O
compression	O
,	O
group-awareness	O
,	O
HTML/XML	O
and	O
tree-structured	O
document	O
editing	O
,	O
collaborative	O
office	O
productivity	O
tools	O
,	O
application-sharing	O
,	O
and	O
collaborative	O
computer-aided	O
media	O
design	O
tools	O
.	O
</s>
<s>
In	O
2009	O
OT	O
was	O
adopted	O
as	O
a	O
core	O
technique	O
behind	O
the	O
collaboration	O
features	O
in	O
Apache	B-Application
Wave	I-Application
and	O
Google	B-Application
Docs	I-Application
.	O
</s>
<s>
Operational	B-Operating_System
Transformation	I-Operating_System
was	O
pioneered	O
by	O
C	O
.	O
Ellis	O
and	O
S	O
.	O
Gibbs	O
in	O
the	O
GROVE	O
(	O
GRoup	O
Outline	O
Viewing	O
Edit	O
)	O
system	O
in	O
1989	O
.	O
</s>
<s>
Since	O
then	O
,	O
SIGCE	O
holds	O
annual	O
CE	O
workshops	O
in	O
conjunction	O
with	O
major	O
CSCW	B-Protocol
(	O
Computer	B-Protocol
Supported	I-Protocol
Cooperative	I-Protocol
Work	I-Protocol
)	O
conferences	O
,	O
such	O
as	O
ACM	O
,	O
CSCW	B-Protocol
,	O
GROUP	O
and	O
ECSCW	O
.	O
</s>
<s>
Collaboration	O
systems	O
utilizing	O
Operational	B-Operating_System
Transformations	I-Operating_System
typically	O
use	O
replicated	O
document	O
storage	O
,	O
where	O
each	O
client	O
has	O
their	O
own	O
copy	O
of	O
the	O
document	O
;	O
clients	O
operate	O
on	O
their	O
local	O
copies	O
in	O
a	O
lock-free	B-Operating_System
,	O
non-blocking	B-Operating_System
manner	O
,	O
and	O
the	O
changes	O
are	O
then	O
propagated	O
to	O
the	O
rest	O
of	O
the	O
clients	O
;	O
this	O
ensures	O
the	O
client	O
high	O
responsiveness	O
in	O
an	O
otherwise	O
high-latency	O
environment	O
such	O
as	O
the	O
Internet	O
.	O
</s>
<s>
When	O
a	O
client	O
receives	O
the	O
changes	O
propagated	O
from	O
another	O
client	O
,	O
it	O
typically	O
transforms	O
the	O
changes	O
before	O
executing	O
them	O
;	O
the	O
transformation	O
ensures	O
that	O
application-dependent	O
consistency	O
criteria	O
(	O
invariants	B-Application
)	O
are	O
maintained	O
by	O
all	O
sites	O
.	O
</s>
<s>
A	O
number	O
of	O
consistency	B-General_Concept
models	I-General_Concept
have	O
been	O
proposed	O
in	O
the	O
research	O
community	O
,	O
some	O
generally	O
for	O
collaborative	O
editing	O
systems	O
,	O
and	O
some	O
specifically	O
for	O
OT	O
algorithms	O
.	O
</s>
<s>
In	O
Ellis	O
and	O
Gibbs	O
1989	O
paper	O
"	O
Concurrency	B-Operating_System
control	I-Operating_System
in	O
groupware	B-Application
systems	O
"	O
,	O
two	O
consistency	O
properties	O
are	O
required	O
for	O
collaborative	O
editing	O
systems	O
:	O
</s>
<s>
The	O
causal	O
relationship	O
between	O
two	O
operations	O
is	O
defined	O
formally	O
by	O
Lamport	O
's	O
"	O
happened-before	B-Operating_System
"	O
relation	O
.	O
</s>
<s>
The	O
first	O
OT	O
algorithm	O
was	O
proposed	O
in	O
Ellis	O
and	O
Gibbs	O
's	O
paper	O
to	O
achieve	O
convergence	O
in	O
a	O
group	O
text	O
editor	O
;	O
the	O
state-vector	O
(	O
or	O
vector	B-Operating_System
clock	I-Operating_System
in	O
classic	O
distributed	O
computing	O
)	O
was	O
used	O
to	O
preserve	O
the	O
precedence	O
property	O
.	O
</s>
<s>
The	O
consistency	B-General_Concept
model	I-General_Concept
proposed	O
in	O
these	O
two	O
approaches	O
consist	O
of	O
the	O
following	O
formal	O
conditions	O
:	O
</s>
<s>
It	O
no	O
longer	O
requires	O
that	O
a	O
total	O
order	O
of	O
objects	O
be	O
specified	O
in	O
the	O
consistency	B-General_Concept
model	I-General_Concept
and	O
maintained	O
in	O
the	O
algorithm	O
,	O
which	O
hence	O
results	O
in	O
reduced	O
time/space	O
complexities	O
in	O
the	O
algorithm	O
.	O
</s>
<s>
the	O
functionality	O
of	O
the	O
OT	O
system	O
:	O
whether	O
the	O
OT	O
system	O
supports	O
do	O
(	O
consistency	O
maintenance	O
)	O
,	O
undo	O
,	O
locking	B-Operating_System
,	O
awareness	O
,	O
application	O
sharing	O
,	O
etc	O
.	O
</s>
<s>
A	O
key	O
differentiating	O
factor	O
is	O
whether	O
an	O
algorithm	O
is	O
capable	O
of	O
supporting	O
concurrency	B-Operating_System
control	I-Operating_System
(	O
do	O
)	O
and/or	O
group	O
undo	O
.	O
</s>
<s>
Most	O
existing	O
OT	O
control	O
algorithms	O
for	O
concurrency	B-Operating_System
control	I-Operating_System
adopt	O
the	O
theory	O
of	O
causality/concurrency	O
as	O
the	O
theoretical	O
basis	O
:	O
causally	O
related	O
operations	O
must	O
be	O
executed	O
in	O
their	O
causal	O
order	O
;	O
concurrent	O
operations	O
must	O
be	O
transformed	O
before	O
their	O
execution	O
.	O
</s>
<s>
?	O
adOPTed	O
(	O
JOINT	O
EMACS	O
)	O
LTransformation	O
(	O
IT	O
)	O
YesChronological	O
UndoIP2	O
,	O
IP3CP1/TP1	O
,	O
CP2/TP2	O
,	O
IP1Causal	O
order	O
State	O
vectorJupiterxform	O
(	O
IT	O
)	O
YesNoCP2/TP2CP1/TP1Causal	O
order	O
+	O
Central	O
transformation	O
serverScalarGoogle	O
Wave	O
OTtransform	O
and	O
composition(IT )	O
YesNoCP2/TP2CP1/TP1Causal	O
order	O
+	O
Central	O
transformation	O
server	O
+	O
stop'n'wait	O
propagation	O
protocolScalar	O
GOT	O
(	O
REDUCE	O
)	O
IT	O
and	O
ET	O
Yes	O
No	O
CP1/TP1	O
,	O
CP2/TP2	O
None	O
Causal	O
order	O
+	O
Discontinuous	O
total	O
order	O
State	O
vector	O
GOTO	O
(	O
REDUCE	O
,	O
CoWord	B-Operating_System
,	O
CoPPT	O
,	O
CoMaya	O
)	O
IT	O
and	O
ET	O
Yes	O
No	O
None	O
CP1/TP1	O
,	O
CP2/TP2	O
Causal	O
order	O
State	O
vector	O
AnyUndo	O
(	O
REDUCE	O
,	O
CoWord	B-Operating_System
,	O
CoPPT	O
,	O
CoMaya	O
)	O
IT	O
and	O
ET	O
No	O
Undo	O
any	O
operation	O
IP2	O
,	O
IP3	O
,	O
RP	O
IP1	O
,	O
CP1/TP1	O
,	O
CP2/TP2	O
Causal	O
order	O
State	O
vector	O
SCOP	O
(	O
NICE	O
)	O
IT	O
Yes	O
No	O
CP2/TP2	O
CP1/TP1	O
Causal	O
order	O
+	O
Central	O
transformation	O
server	O
Scalar	O
COT	O
(	O
REDUCE	O
,	O
CoWord	B-Operating_System
,	O
CoPPT	O
,	O
CoMaya	O
)	O
IT	O
Yes	O
Undo	O
any	O
operation	O
CP2/TP2	O
,	O
IP2	O
,	O
IP3	O
CP1/TP1	O
,	O
(	O
no	O
ET	O
therefore	O
no	O
IP1	O
necessary	O
)	O
Causal	O
order	O
+	O
Discontinuous	O
total	O
order	O
Context	O
vectorTIBOT	O
IT	O
Yes	O
No	O
CP2/TP2	O
CP1/TP1	O
Causal	O
order	O
Scalar	O
SOCT4	O
Forward	O
transformation	O
(	O
IT	O
)	O
Yes	O
No	O
CP2/TP2	O
CP1/TP1	O
Causal	O
order	O
+	O
Continuous	O
total	O
order	O
Scalar	O
SOCT2	O
Forward	O
Transformation(IT )	O
and	O
Backward	O
Transformation(ET )	O
Yes	O
No	O
None	O
CP1/TP1	O
,	O
CP2/TP2	O
,	O
RP	O
Causal	O
order	O
State	O
vector	O
MOT2	O
Forward	O
transformation	O
(	O
IT	O
)	O
Yes	O
No	O
?	O
</s>
<s>
The	O
transformation-based	O
algorithms	O
proposed	O
in	O
are	O
based	O
on	O
the	O
alternative	O
consistency	B-General_Concept
models	I-General_Concept
"	O
CSM	O
"	O
and	O
"	O
CA	O
"	O
as	O
described	O
above	O
.	O
</s>
<s>
Similarly	O
,	O
Joseph	O
Gentle	O
who	O
is	O
a	O
former	O
Google	B-Application
Wave	I-Application
engineer	O
and	O
an	O
author	O
of	O
the	O
Share.JS	O
library	O
wrote	O
,	O
"	O
Unfortunately	O
,	O
implementing	O
OT	O
sucks	O
.	O
</s>
<s>
Another	O
alternative	O
to	O
OT	O
is	O
using	O
sequence	O
types	O
of	O
conflict-free	B-Operating_System
replicated	I-Operating_System
data	I-Operating_System
type	I-Operating_System
.	O
</s>
