<s>
Kepler	O
is	O
a	O
free	B-Application
software	I-Application
system	O
for	O
designing	O
,	O
executing	O
,	O
reusing	O
,	O
evolving	O
,	O
archiving	O
,	O
and	O
sharing	O
scientific	B-Application
workflows	I-Application
.	O
</s>
<s>
Workflows	O
in	O
general	O
,	O
and	O
scientific	B-Application
workflows	I-Application
in	O
particular	O
,	O
are	O
directed	O
graphs	O
where	O
the	O
nodes	O
represent	O
discrete	O
computational	O
components	O
,	O
and	O
the	O
edges	O
represent	O
paths	O
along	O
which	O
data	O
and	O
results	O
can	O
flow	O
between	O
components	O
.	O
</s>
<s>
Kepler	O
includes	O
a	O
graphical	O
user	O
interface	O
for	O
composing	O
workflows	O
in	O
a	O
desktop	O
environment	O
,	O
a	O
runtime	O
engine	O
for	O
executing	O
workflows	O
within	O
the	O
GUI	O
and	O
independently	O
from	O
a	O
command-line	O
,	O
and	O
a	O
distributed	O
computing	O
option	O
that	O
allows	O
workflow	O
tasks	O
to	O
be	O
distributed	O
among	O
compute	O
nodes	O
in	O
a	O
computer	B-Architecture
cluster	I-Architecture
or	O
computing	B-Architecture
grid	I-Architecture
.	O
</s>
<s>
Thus	O
,	O
Kepler	O
scientific	B-Application
workflows	I-Application
generally	O
model	O
the	O
flow	O
of	O
data	O
from	O
one	O
step	O
to	O
another	O
in	O
a	O
series	O
of	O
computations	O
that	O
achieve	O
some	O
scientific	O
goal	O
.	O
</s>
<s>
Scientific	B-Application
workflow	I-Application
systems	I-Application
often	O
provide	O
graphical	O
user	O
interfaces	O
to	O
combine	O
different	O
technologies	O
along	O
with	O
efficient	O
methods	O
for	O
using	O
them	O
,	O
and	O
thus	O
increase	O
the	O
efficiency	O
of	O
the	O
scientists	O
.	O
</s>
<s>
Additional	O
data	O
sources	O
that	O
are	O
supported	O
include	O
data	O
accessible	O
using	O
the	O
DiGIR	O
protocol	O
,	O
the	O
OPeNDAP	B-Application
protocol	O
,	O
GridFTP	O
,	O
JDBC	B-Language
,	O
SRB	B-Operating_System
,	O
and	O
others	O
.	O
</s>
<s>
Kepler	O
differs	O
from	O
many	O
of	O
the	O
other	O
bioinformatics	B-Application
workflow	I-Application
management	I-Application
systems	I-Application
in	O
that	O
it	O
separates	O
the	O
structure	O
of	O
the	O
workflow	O
model	O
from	O
its	O
model	O
of	O
computation	O
,	O
such	O
that	O
different	O
models	O
for	O
the	O
computation	O
of	O
the	O
workflow	O
can	O
be	O
bound	O
to	O
a	O
given	O
workflow	O
graph	O
.	O
</s>
<s>
Kepler	O
inherits	O
several	O
common	O
models	O
of	O
computation	O
from	O
the	O
Ptolemy	B-Application
system	I-Application
,	O
including	O
Synchronous	O
Data	O
Flow	O
(	O
SDF	O
)	O
,	O
Continuous	O
Time	O
(	O
CT	O
)	O
,	O
Process	O
Network	O
(	O
PN	O
)	O
,	O
and	O
Dynamic	O
Data	O
Flow	O
(	O
DDF	O
)	O
,	O
among	O
others	O
.	O
</s>
<s>
Kepler	O
components	O
can	O
be	O
shared	O
by	O
exporting	O
the	O
workflow	O
or	O
component	O
into	O
a	O
Kepler	O
Archive	O
(	O
KAR	O
)	O
file	O
,	O
which	O
is	O
an	O
extension	O
of	O
the	O
JAR	B-Language
file	I-Language
format	I-Language
from	O
Java	B-Language
.	O
</s>
<s>
Provenance	O
is	O
a	O
critical	O
concept	O
in	O
scientific	B-Application
workflows	I-Application
,	O
since	O
it	O
allows	O
scientists	O
to	O
understand	O
the	O
origin	O
of	O
their	O
results	O
,	O
to	O
repeat	O
their	O
experiments	O
,	O
and	O
to	O
validate	O
the	O
processes	O
that	O
were	O
used	O
to	O
derive	O
data	O
products	O
.	O
</s>
<s>
Collaboration	O
on	O
Kepler	O
quickly	O
grew	O
as	O
members	O
of	O
various	O
scientific	O
disciplines	O
realized	O
the	O
benefits	O
of	O
scientific	B-Application
workflows	I-Application
for	O
analysis	O
and	O
modeling	O
and	O
began	O
contributing	O
to	O
the	O
system	O
.	O
</s>
