<s>
Software	B-General_Concept
entropy	I-General_Concept
is	O
the	O
idea	O
that	O
software	O
eventually	O
rots	O
as	O
it	O
is	O
changed	O
if	O
sufficient	O
care	O
is	O
not	O
taken	O
to	O
maintain	O
coherence	O
with	O
product	O
design	O
and	O
established	O
design	O
principles	O
.	O
</s>
<s>
The	O
common	O
usage	O
is	O
only	O
tangentially	O
related	O
to	O
entropy	B-Algorithm
as	O
defined	O
in	O
classical	O
thermodynamics	O
and	O
statistical	O
physics	O
.	O
</s>
<s>
A	O
work	O
on	O
software	B-General_Concept
engineering	I-General_Concept
by	O
Ivar	O
Jacobson	O
et	O
al	O
,	O
in	O
1992	O
describes	O
software	B-General_Concept
entropy	I-General_Concept
as	O
follows	O
:	O
</s>
<s>
The	O
second	O
law	O
of	O
thermodynamics	O
,	O
in	O
principle	O
,	O
states	O
that	O
a	O
closed	B-Operating_System
system	I-Operating_System
's	O
disorder	O
cannot	O
be	O
reduced	O
,	O
it	O
can	O
only	O
remain	O
unchanged	O
or	O
increase	O
.	O
</s>
<s>
A	O
measure	O
of	O
this	O
disorder	O
is	O
entropy	B-Algorithm
.	O
</s>
<s>
This	O
law	O
also	O
seems	O
plausible	O
for	O
software	O
systems	O
;	O
as	O
a	O
system	O
is	O
modified	O
,	O
its	O
disorder	O
,	O
or	O
entropy	B-Algorithm
,	O
tends	O
to	O
increase	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
software	B-General_Concept
entropy	I-General_Concept
.	O
</s>
<s>
In	O
1999	O
,	O
Andrew	O
Hunt	O
and	O
David	O
Thomas	O
use	O
fixing	O
broken	O
windows	O
as	O
a	O
metaphor	O
for	O
avoiding	O
software	B-General_Concept
entropy	I-General_Concept
in	O
software	O
development	O
.	O
</s>
<s>
The	O
purpose	O
of	O
writing	O
software	O
is	O
to	O
encode	B-Algorithm
domain	O
and	O
design	O
knowledge	O
,	O
in	O
source	O
form(s )	O
that	O
can	O
be	O
translated	O
to	O
executable	O
destination	O
format(s )	O
.	O
</s>
<s>
As	O
such	O
,	O
to	O
the	O
extent	O
that	O
the	O
source	O
is	O
a	O
coherent	O
,	O
noise	O
free	O
encoding	B-Algorithm
of	O
the	O
relevant	O
knowledge	O
sets	O
,	O
its	O
entropy	B-Algorithm
may	O
be	O
considered	O
to	O
be	O
low	O
.	O
</s>
<s>
After	O
initial	O
development	O
and	O
acceptance	O
,	O
the	O
code	O
enters	O
the	O
maintenance	O
phase	O
of	O
the	O
software	O
lifecycle	O
,	O
where	O
it	O
may	O
be	O
allowed	O
to	O
accumulate	O
defects	O
(	O
noise	O
)	O
,	O
represented	O
by	O
divergence	O
from	O
those	O
knowledge	O
sets	O
(	O
domain	O
and	O
software	O
design	O
principles	O
)	O
,	O
and	O
thereby	O
increase	O
the	O
entropy	B-Algorithm
of	O
the	O
software	O
.	O
</s>
<s>
While	O
there	O
are	O
known	O
correlations	O
(	O
see	O
software	O
complexity	O
)	O
,	O
there	O
is	O
no	O
direct	O
relationship	O
between	O
software	O
complexity	O
and	O
software	B-General_Concept
entropy	I-General_Concept
.	O
</s>
<s>
Any	O
two	O
pieces	O
of	O
software	O
,	O
with	O
equivalent	O
complexity	O
levels	O
,	O
can	O
exist	O
at	O
different	O
levels	O
of	O
entropy	B-Algorithm
or	O
rot	O
.	O
</s>
<s>
Even	O
a	O
very	O
simple	O
program	O
,	O
can	O
suffer	O
high	O
levels	O
of	O
entropy	B-Algorithm
as	O
it	O
passes	O
through	O
the	O
hands	O
of	O
multiple	O
developers	O
.	O
</s>
<s>
The	O
process	O
of	O
code	O
refactoring	O
can	O
result	O
in	O
stepwise	O
reductions	O
in	O
software	B-General_Concept
entropy	I-General_Concept
.	O
</s>
