<s>
An	O
application	B-Application
protocol-based	I-Application
intrusion	I-Application
detection	I-Application
system	I-Application
(	O
APIDS	B-Application
)	O
is	O
an	O
intrusion	O
detection	O
system	O
that	O
focuses	O
its	O
monitoring	B-Application
and	O
analysis	O
on	O
a	O
specific	O
application	O
protocol	O
or	O
protocols	O
in	O
use	O
by	O
the	O
computing	O
system	O
.	O
</s>
<s>
An	O
APIDS	B-Application
will	O
monitor	O
the	O
dynamic	O
behavior	O
and	O
state	B-Application
of	O
the	O
protocol	O
and	O
will	O
typically	O
consist	O
of	O
a	O
system	O
or	O
agent	O
that	O
would	O
typically	O
sit	O
between	O
a	O
process	B-Operating_System
,	O
or	O
group	O
of	O
servers	O
,	O
monitoring	B-Application
and	O
analyzing	O
the	O
application	O
protocol	O
between	O
two	O
connected	O
devices	O
.	O
</s>
<s>
A	O
typical	O
place	O
for	O
an	O
APIDS	B-Application
would	O
be	O
between	O
a	O
web	B-Application
server	I-Application
and	O
the	O
database	B-Application
management	I-Application
system	I-Application
,	O
monitoring	B-Application
the	O
SQL	B-Language
protocol	O
specific	O
to	O
the	O
middleware/business	O
logic	O
as	O
it	O
interacts	O
with	O
the	O
database	O
.	O
</s>
<s>
At	O
a	O
basic	O
level	O
an	O
APIDS	B-Application
would	O
look	O
for	O
,	O
and	O
enforce	O
,	O
the	O
correct	O
(	O
legal	O
)	O
use	O
of	O
the	O
protocol	O
.	O
</s>
<s>
However	O
at	O
a	O
more	O
advanced	O
level	O
the	O
APIDS	B-Application
can	O
learn	O
,	O
be	O
taught	O
or	O
even	O
reduce	O
what	O
is	O
often	O
an	O
infinite	O
protocol	O
set	O
,	O
to	O
an	O
acceptable	O
understanding	O
of	O
the	O
subset	O
of	O
that	O
application	O
protocol	O
that	O
is	O
used	O
by	O
the	O
application	O
being	O
monitored/protected	O
.	O
</s>
<s>
Thus	O
,	O
an	O
APIDS	B-Application
,	O
correctly	O
configured	O
,	O
will	O
allow	O
an	O
application	O
to	O
be	O
"	O
fingerprinted	O
"	O
,	O
thus	O
should	O
that	O
application	O
be	O
subverted	O
or	O
changed	O
,	O
so	O
will	O
the	O
fingerprint	B-Algorithm
change	O
.	O
</s>
