<s>
PLEXIL	B-Language
(	O
Plan	B-Language
Execution	I-Language
Interchange	I-Language
Language	I-Language
)	O
is	O
an	O
open	O
source	O
technology	O
for	O
automation	B-Application
,	O
created	O
and	O
currently	O
in	O
development	O
by	O
NASA	O
.	O
</s>
<s>
PLEXIL	B-Language
is	O
a	O
programming	O
language	O
for	O
representing	O
plans	O
for	O
automation	B-Application
.	O
</s>
<s>
PLEXIL	B-Language
is	O
used	O
in	O
automation	B-Application
technologies	O
such	O
as	O
the	O
NASA	O
K10	O
rover	O
,	O
Mars	O
Curiosity	O
rover	O
's	O
percussion	O
drill	O
,	O
Deep	O
Space	O
Habitat	O
and	O
Habitat	O
Demonstration	O
Unit	O
,	O
Edison	O
Demonstration	O
of	O
Smallsat	O
Networks	O
,	O
LADEE	O
,	O
Autonomy	O
Operating	O
System	O
(	O
AOS	O
)	O
and	O
procedure	O
automation	B-Application
for	O
the	O
International	O
Space	O
Station	O
.	O
</s>
<s>
The	O
PLEXIL	B-Language
Executive	O
is	O
an	O
execution	B-General_Concept
engine	O
that	O
implements	O
PLEXIL	B-Language
and	O
can	O
be	O
interfaced	O
(	O
using	O
a	O
provided	O
software	O
framework	O
)	O
with	O
external	O
systems	O
to	O
be	O
controlled	O
and/or	O
queried	O
.	O
</s>
<s>
PLEXIL	B-Language
has	O
been	O
used	O
to	O
demonstrate	O
automation	B-Application
technologies	O
targeted	O
at	O
future	O
NASA	O
space	O
missions	O
.	O
</s>
<s>
The	O
binaries	O
and	O
documentation	O
are	O
widely	O
available	O
as	O
BSD	O
licensed	O
open	O
source	O
from	O
SourceForge.net	B-Application
.	O
</s>
<s>
The	O
fundamental	O
programming	O
unit	O
of	O
PLEXIL	B-Language
is	O
the	O
Node	O
.	O
</s>
<s>
A	O
node	O
is	O
a	O
data	B-General_Concept
structure	I-General_Concept
formed	O
of	O
two	O
primary	O
components	O
:	O
a	O
set	O
of	O
conditions	B-Language
that	O
drive	O
the	O
execution	B-General_Concept
of	O
the	O
node	O
and	O
another	O
set	O
which	O
specifies	O
what	O
the	O
node	O
accomplishes	O
after	O
execution	B-General_Concept
.	O
</s>
