<s>
In	O
computing	O
,	O
aspect-oriented	B-Architecture
programming	I-Architecture
(	O
AOP	O
)	O
is	O
a	O
programming	O
paradigm	O
that	O
aims	O
to	O
increase	O
modularity	B-Architecture
by	O
allowing	O
the	O
separation	O
of	O
cross-cutting	B-Application
concerns	I-Application
.	O
</s>
<s>
It	O
does	O
so	O
by	O
adding	O
behavior	O
to	O
existing	O
code	O
(	O
an	O
advice	B-Application
)	O
without	O
modifying	O
the	O
code	O
itself	O
,	O
instead	O
separately	O
specifying	O
which	O
code	O
is	O
modified	O
via	O
a	O
"	O
pointcut	B-Application
"	O
specification	O
,	O
such	O
as	O
"	O
log	O
all	O
function	O
calls	O
when	O
the	O
function	O
's	O
name	O
begins	O
with	O
'	O
set	O
.	O
</s>
<s>
This	O
allows	O
behaviors	O
that	O
are	O
not	O
central	O
to	O
the	O
business	B-Architecture
logic	I-Architecture
(	O
such	O
as	O
logging	O
)	O
to	O
be	O
added	O
to	O
a	O
program	O
without	O
cluttering	O
the	O
code	O
core	O
to	O
the	O
functionality	O
.	O
</s>
<s>
AOP	O
includes	O
programming	O
methods	O
and	O
tools	O
that	O
support	O
the	O
modularization	O
of	O
concerns	O
at	O
the	O
level	O
of	O
the	O
source	O
code	O
,	O
while	O
aspect-oriented	B-Architecture
software	I-Architecture
development	I-Architecture
refers	O
to	O
a	O
whole	O
engineering	O
discipline	O
.	O
</s>
<s>
Aspect-oriented	B-Architecture
programming	I-Architecture
entails	O
breaking	O
down	O
program	O
logic	O
into	O
distinct	O
parts	O
(	O
so-called	O
concerns	O
,	O
cohesive	O
areas	O
of	O
functionality	O
)	O
.	O
</s>
<s>
Nearly	O
all	O
programming	O
paradigms	O
support	O
some	O
level	O
of	O
grouping	O
and	O
encapsulation	B-Application
of	O
concerns	O
into	O
separate	O
,	O
independent	O
entities	O
by	O
providing	O
abstractions	O
(	O
e.g.	O
,	O
functions	O
,	O
procedures	O
,	O
modules	B-Architecture
,	O
classes	O
,	O
methods	O
)	O
that	O
can	O
be	O
used	O
for	O
implementing	O
,	O
abstracting	O
and	O
composing	O
these	O
concerns	O
.	O
</s>
<s>
These	O
concerns	O
are	O
called	O
cross-cutting	B-Application
concerns	I-Application
or	O
horizontal	O
concerns	O
.	O
</s>
<s>
Logging	O
exemplifies	O
a	O
crosscutting	B-Application
concern	I-Application
because	O
a	O
logging	O
strategy	O
necessarily	O
affects	O
every	O
logged	O
part	O
of	O
the	O
system	O
.	O
</s>
<s>
AspectJ	B-Application
has	O
a	O
number	O
of	O
such	O
expressions	O
and	O
encapsulates	O
them	O
in	O
a	O
special	O
class	O
,	O
an	O
aspect	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
an	O
aspect	B-Application
can	O
alter	O
the	O
behavior	O
of	O
the	O
base	O
code	O
(	O
the	O
non-aspect	O
part	O
of	O
a	O
program	O
)	O
by	O
applying	O
advice	B-Application
(	O
additional	O
behavior	O
)	O
at	O
various	O
join	B-Application
points	I-Application
(	O
points	O
in	O
a	O
program	O
)	O
specified	O
in	O
a	O
quantification	O
or	O
query	O
called	O
a	O
pointcut	B-Application
(	O
that	O
detects	O
whether	O
a	O
given	O
join	B-Application
point	I-Application
matches	O
)	O
.	O
</s>
<s>
An	O
aspect	B-Application
can	O
also	O
make	B-Application
binary-compatible	O
structural	O
changes	O
to	O
other	O
classes	O
,	O
like	O
adding	O
members	O
or	O
parents	O
.	O
</s>
<s>
AOP	O
has	O
several	O
direct	O
antecedents	O
A1	O
and	O
A2	O
:	O
reflection	B-Language
and	O
metaobject	O
protocols	O
,	O
subject-oriented	B-Application
programming	I-Application
,	O
Composition	O
Filters	O
and	O
Adaptive	O
Programming	O
.	O
</s>
<s>
Gregor	O
Kiczales	O
and	O
colleagues	O
at	O
Xerox	O
PARC	O
developed	O
the	O
explicit	O
concept	O
of	O
AOP	O
,	O
and	O
followed	O
this	O
with	O
the	O
AspectJ	B-Application
AOP	O
extension	O
to	O
Java	B-Language
.	O
</s>
<s>
The	O
examples	O
in	O
this	O
article	O
use	O
AspectJ	B-Application
.	O
</s>
<s>
The	O
Microsoft	B-Operating_System
Transaction	I-Operating_System
Server	I-Operating_System
is	O
considered	O
to	O
be	O
the	O
first	O
major	O
application	O
of	O
AOP	O
followed	O
by	O
Enterprise	B-Language
JavaBeans	I-Language
.	O
</s>
<s>
Typically	O
,	O
an	O
aspect	B-Application
is	O
scattered	O
or	O
tangled	O
as	O
code	O
,	O
making	O
it	O
harder	O
to	O
understand	O
and	O
maintain	O
.	O
</s>
<s>
That	O
means	O
to	O
change	O
logging	O
can	O
require	O
modifying	O
all	O
affected	O
modules	B-Architecture
.	O
</s>
<s>
However	O
,	O
this	O
transfer	O
method	O
overlooks	O
certain	O
considerations	O
that	O
a	O
deployed	O
application	O
would	O
require	O
:	O
it	O
lacks	O
security	O
checks	O
to	O
verify	O
that	O
the	O
current	O
user	O
has	O
the	O
authorization	O
to	O
perform	O
this	O
operation	O
;	O
a	O
database	B-General_Concept
transaction	I-General_Concept
should	O
encapsulate	O
the	O
operation	O
in	O
order	O
to	O
prevent	O
accidental	O
data	O
loss	O
;	O
for	O
diagnostics	O
,	O
the	O
operation	O
should	O
be	O
logged	O
to	O
the	O
system	O
log	O
,	O
etc	O
.	O
</s>
<s>
In	O
this	O
example	O
,	O
other	O
interests	O
have	O
become	O
tangled	O
with	O
the	O
basic	O
functionality	O
(	O
sometimes	O
called	O
the	O
business	B-Architecture
logic	I-Architecture
concern	O
)	O
.	O
</s>
<s>
Transactions	O
,	O
security	O
,	O
and	O
logging	O
all	O
exemplify	O
cross-cutting	B-Application
concerns	I-Application
.	O
</s>
<s>
AOP	O
attempts	O
to	O
solve	O
this	O
problem	O
by	O
allowing	O
the	O
programmer	O
to	O
express	O
cross-cutting	B-Application
concerns	I-Application
in	O
stand-alone	O
modules	B-Architecture
called	O
aspects	O
.	O
</s>
<s>
Aspects	O
can	O
contain	O
advice	B-Application
(	O
code	O
joined	O
to	O
specified	O
points	O
in	O
the	O
program	O
)	O
and	O
inter-type	O
declarations	O
(	O
structural	O
members	O
added	O
to	O
other	O
classes	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
security	O
module	B-Architecture
can	O
include	O
advice	B-Application
that	O
performs	O
a	O
security	O
check	O
before	O
accessing	O
a	O
bank	O
account	O
.	O
</s>
<s>
The	O
pointcut	B-Application
defines	O
the	O
times	O
(	O
join	B-Application
points	I-Application
)	O
when	O
one	O
can	O
access	O
a	O
bank	O
account	O
,	O
and	O
the	O
code	O
in	O
the	O
advice	B-Application
body	O
defines	O
how	O
the	O
security	O
check	O
is	O
implemented	O
.	O
</s>
<s>
Further	O
,	O
a	O
good	O
pointcut	B-Application
can	O
anticipate	O
later	O
program	O
changes	O
,	O
so	O
if	O
another	O
developer	O
creates	O
a	O
new	O
method	O
to	O
access	O
the	O
bank	O
account	O
,	O
the	O
advice	B-Application
will	O
apply	O
to	O
the	O
new	O
method	O
when	O
it	O
executes	O
.	O
</s>
<s>
So	O
for	O
the	O
example	O
above	O
implementing	O
logging	O
in	O
an	O
aspect	B-Application
:	O
</s>
<s>
Advice	B-Application
should	O
be	O
reserved	O
for	O
the	O
cases	O
where	O
you	O
cannot	O
get	O
the	O
function	O
changed	O
(	O
user	O
level	O
)	O
or	O
do	O
not	O
want	O
to	O
change	O
the	O
function	O
in	O
production	O
code	O
(	O
debugging	O
)	O
.	O
</s>
<s>
The	O
advice-related	O
component	O
of	O
an	O
aspect-oriented	B-Architecture
language	I-Architecture
defines	O
a	O
join	B-Application
point	I-Application
model	O
(	O
JPM	O
)	O
.	O
</s>
<s>
When	O
the	O
advice	B-Application
can	O
run	O
.	O
</s>
<s>
These	O
are	O
called	O
join	B-Application
points	I-Application
because	O
they	O
are	O
points	O
in	O
a	O
running	O
program	O
where	O
additional	O
behavior	O
can	O
be	O
usefully	O
joined	O
.	O
</s>
<s>
A	O
join	B-Application
point	I-Application
needs	O
to	O
be	O
addressable	O
and	O
understandable	O
by	O
an	O
ordinary	O
programmer	O
to	O
be	O
useful	O
.	O
</s>
<s>
It	O
should	O
also	O
be	O
stable	O
across	O
inconsequential	O
program	O
changes	O
in	O
order	O
for	O
an	O
aspect	B-Application
to	O
be	O
stable	O
across	O
such	O
changes	O
.	O
</s>
<s>
Many	O
AOP	O
implementations	O
support	O
method	O
executions	O
and	O
field	O
references	O
as	O
join	B-Application
points	I-Application
.	O
</s>
<s>
A	O
way	O
to	O
specify	O
(	O
or	O
quantify	O
)	O
join	B-Application
points	I-Application
,	O
called	O
pointcuts	B-Application
.	O
</s>
<s>
Pointcuts	B-Application
determine	O
whether	O
a	O
given	O
join	B-Application
point	I-Application
matches	O
.	O
</s>
<s>
Most	O
useful	O
pointcut	B-Application
languages	O
use	O
a	O
syntax	O
like	O
the	O
base	O
language	O
(	O
for	O
example	O
,	O
AspectJ	B-Application
uses	O
Java	B-Language
signatures	O
)	O
and	O
allow	O
reuse	O
through	O
naming	O
and	O
combination	O
.	O
</s>
<s>
A	O
means	O
of	O
specifying	O
code	O
to	O
run	O
at	O
a	O
join	B-Application
point	I-Application
.	O
</s>
<s>
AspectJ	B-Application
calls	O
this	O
advice	B-Application
,	O
and	O
can	O
run	O
it	O
before	O
,	O
after	O
,	O
and	O
around	O
join	B-Application
points	I-Application
.	O
</s>
<s>
Some	O
implementations	O
also	O
support	O
things	O
like	O
defining	O
a	O
method	O
in	O
an	O
aspect	B-Application
on	O
another	O
class	O
.	O
</s>
<s>
Join-point	B-Application
models	O
can	O
be	O
compared	O
based	O
on	O
the	O
join	B-Application
points	I-Application
exposed	O
,	O
how	O
join	B-Application
points	I-Application
are	O
specified	O
,	O
the	O
operations	O
permitted	O
at	O
the	O
join	B-Application
points	I-Application
,	O
and	O
the	O
structural	O
enhancements	O
that	O
can	O
be	O
expressed	O
.	O
</s>
<s>
All	O
advice	B-Application
languages	O
can	O
be	O
defined	O
in	O
terms	O
of	O
their	O
JPM	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
hypothetical	O
aspect	B-Application
language	O
for	O
UML	B-Language
may	O
have	O
the	O
following	O
JPM	O
:	O
</s>
<s>
Join	B-Application
points	I-Application
are	O
all	O
model	O
elements	O
.	O
</s>
<s>
Pointcuts	B-Application
are	O
some	O
boolean	O
expression	O
combining	O
the	O
model	O
elements	O
.	O
</s>
<s>
The	O
means	O
of	O
affect	O
at	O
these	O
points	O
are	O
a	O
visualization	O
of	O
all	O
the	O
matched	O
join	B-Application
points	I-Application
.	O
</s>
<s>
Inter-type	O
declarations	O
provide	O
a	O
way	O
to	O
express	O
crosscutting	B-Application
concerns	I-Application
affecting	O
the	O
structure	O
of	O
modules	B-Architecture
.	O
</s>
<s>
Also	O
known	O
as	O
open	O
classes	O
and	O
extension	O
methods	O
,	O
this	O
enables	O
programmers	O
to	O
declare	O
in	O
one	O
place	O
members	O
or	O
parents	O
of	O
another	O
class	O
,	O
typically	O
in	O
order	O
to	O
combine	O
all	O
the	O
code	O
related	O
to	O
a	O
concern	O
in	O
one	O
aspect	B-Application
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
programmer	O
implemented	O
the	O
crosscutting	O
display-update	O
concern	O
using	O
visitors	O
instead	O
,	O
an	O
inter-type	O
declaration	O
using	O
the	O
visitor	B-Language
pattern	I-Language
might	O
look	O
like	O
this	O
in	O
AspectJ	B-Application
:	O
</s>
<s>
The	O
difficulty	O
of	O
changing	O
environments	O
means	O
most	O
implementations	O
produce	O
compatible	O
combination	O
programs	O
through	O
a	O
type	O
of	O
program	B-Application
transformation	I-Application
known	O
as	O
weaving	O
.	O
</s>
<s>
An	O
aspect	B-Application
weaver	I-Application
reads	O
the	O
aspect-oriented	B-Architecture
code	O
and	O
generates	O
appropriate	O
object-oriented	B-Language
code	I-Language
with	O
the	O
aspects	O
integrated	O
.	O
</s>
<s>
Systems	O
can	O
implement	O
source-level	O
weaving	O
using	O
preprocessors	O
(	O
as	O
C++	B-Language
was	O
implemented	O
originally	O
in	O
CFront	B-Device
)	O
that	O
require	O
access	O
to	O
program	O
source	O
files	O
.	O
</s>
<s>
However	O
,	O
Java	B-Language
's	O
well-defined	O
binary	O
form	O
enables	O
bytecode	O
weavers	O
to	O
work	O
with	O
any	O
Java	B-Language
program	O
in	O
.class-file	O
form	O
.	O
</s>
<s>
AspectJ	B-Application
started	O
with	O
source-level	O
weaving	O
in	O
2001	O
,	O
delivered	O
a	O
per-class	O
bytecode	O
weaver	O
in	O
2002	O
,	O
and	O
offered	O
advanced	O
load-time	O
support	O
after	O
the	O
integration	O
of	O
AspectWerkz	B-Application
in	O
2005	O
.	O
</s>
<s>
Java	B-Language
's	O
bytecode	O
support	O
for	O
multiple	O
source	O
files	O
enables	O
any	O
debugger	O
to	O
step	O
through	O
a	O
properly	O
woven	O
.class	O
file	O
in	O
a	O
source	O
editor	O
.	O
</s>
<s>
A	O
similar	O
approach	O
has	O
already	O
proven	O
itself	O
in	O
the	O
implementation	O
of	O
many	O
Java	B-Language
EE	I-Language
application	O
servers	O
,	O
such	O
as	O
IBM	O
's	O
WebSphere	B-Language
.	O
</s>
<s>
Standard	O
terminology	O
used	O
in	O
Aspect-oriented	B-Architecture
programming	I-Architecture
may	O
include	O
:	O
</s>
<s>
Cross-cutting	B-Application
concerns	I-Application
Even	O
though	O
most	O
classes	O
in	O
an	O
OO	O
model	O
will	O
perform	O
a	O
single	O
,	O
specific	O
function	O
,	O
they	O
often	O
share	O
common	O
,	O
secondary	O
requirements	O
with	O
other	O
classes	O
.	O
</s>
<s>
Advice	B-Application
This	O
is	O
the	O
additional	O
code	O
that	O
you	O
want	O
to	O
apply	O
to	O
your	O
existing	O
model	O
.	O
</s>
<s>
Pointcut	B-Application
This	O
is	O
the	O
term	O
given	O
to	O
the	O
point	O
of	O
execution	O
in	O
the	O
application	O
at	O
which	O
cross-cutting	B-Application
concern	I-Application
needs	O
to	O
be	O
applied	O
.	O
</s>
<s>
In	O
our	O
example	O
,	O
a	O
pointcut	B-Application
is	O
reached	O
when	O
the	O
thread	O
enters	O
a	O
method	O
,	O
and	O
another	O
pointcut	B-Application
is	O
reached	O
when	O
the	O
thread	O
exits	O
the	O
method	O
.	O
</s>
<s>
Aspect	B-Application
The	O
combination	O
of	O
the	O
pointcut	B-Application
and	O
the	O
advice	B-Application
is	O
termed	O
an	O
aspect	B-Application
.	O
</s>
<s>
In	O
the	O
example	O
above	O
,	O
we	O
add	O
a	O
logging	O
aspect	B-Application
to	O
our	O
application	O
by	O
defining	O
a	O
pointcut	B-Application
and	O
giving	O
the	O
correct	O
advice	B-Application
.	O
</s>
<s>
Aspects	O
emerged	O
from	O
object-oriented	B-Language
programming	I-Language
and	O
computational	B-Language
reflection	I-Language
.	O
</s>
<s>
Aspects	O
relate	O
closely	O
to	O
programming	O
concepts	O
like	O
subjects	B-Application
,	O
mixins	B-Language
,	O
and	O
delegation	O
.	O
</s>
<s>
Other	O
ways	O
to	O
use	O
aspect-oriented	B-Architecture
programming	I-Architecture
paradigms	O
include	O
Composition	O
Filters	O
and	O
the	O
hyperslices	O
approach	O
.	O
</s>
<s>
Designers	O
have	O
considered	O
alternative	O
ways	O
to	O
achieve	O
separation	O
of	O
code	O
,	O
such	O
as	O
C#'s	O
partial	O
types	O
,	O
but	O
such	O
approaches	O
lack	O
a	O
quantification	O
mechanism	O
that	O
allows	O
reaching	O
several	O
join	B-Application
points	I-Application
of	O
the	O
code	O
with	O
one	O
declarative	O
statement	O
.	O
</s>
<s>
Though	O
it	O
may	O
seem	O
unrelated	O
,	O
in	O
testing	O
,	O
the	O
use	O
of	O
mocks	O
or	O
stubs	O
requires	O
the	O
use	O
of	O
AOP	O
techniques	O
,	O
like	O
around	O
advice	B-Application
,	O
and	O
so	O
forth	O
.	O
</s>
<s>
Here	O
the	O
collaborating	O
objects	O
are	O
for	O
the	O
purpose	O
of	O
the	O
test	O
,	O
a	O
cross	B-Application
cutting	I-Application
concern	O
.	O
</s>
<s>
Even	O
with	O
proper	O
education	O
,	O
understanding	O
crosscutting	B-Application
concerns	I-Application
can	O
be	O
difficult	O
without	O
proper	O
support	O
for	O
visualizing	O
both	O
static	O
structure	O
and	O
the	O
dynamic	O
flow	O
of	O
a	O
program	O
.	O
</s>
<s>
Beginning	O
in	O
2002	O
,	O
AspectJ	B-Application
began	O
to	O
provide	O
IDE	O
plug-ins	O
to	O
support	O
the	O
visualizing	O
of	O
crosscutting	B-Application
concerns	I-Application
.	O
</s>
<s>
Those	O
features	O
,	O
as	O
well	O
as	O
aspect	B-Application
code	O
assist	O
and	O
refactoring	O
are	O
now	O
common	O
.	O
</s>
<s>
Conversely	O
,	O
another	O
programmer	O
may	O
change	O
the	O
join	B-Application
points	I-Application
in	O
a	O
program	O
e.g.	O
,	O
by	O
renaming	O
or	O
moving	O
methods	O
in	O
ways	O
that	O
the	O
aspect	B-Application
writer	O
did	O
not	O
anticipate	O
,	O
with	O
unforeseen	O
consequences	O
.	O
</s>
<s>
One	O
advantage	O
of	O
modularizing	O
crosscutting	B-Application
concerns	I-Application
is	O
enabling	O
one	O
programmer	O
to	O
affect	O
the	O
entire	O
system	O
easily	O
;	O
as	O
a	O
result	O
,	O
such	O
problems	O
present	O
as	O
a	O
conflict	O
over	O
responsibility	O
between	O
two	O
or	O
more	O
developers	O
for	O
a	O
given	O
failure	O
.	O
</s>
<s>
However	O
,	O
the	O
solution	O
for	O
these	O
problems	O
can	O
be	O
much	O
easier	O
in	O
the	O
presence	O
of	O
AOP	O
,	O
since	O
only	O
the	O
aspect	B-Application
needs	O
to	O
be	O
changed	O
,	O
whereas	O
the	O
corresponding	O
problems	O
without	O
AOP	O
can	O
be	O
much	O
more	O
spread	O
out	O
.	O
</s>
<s>
The	O
most	O
basic	O
criticism	O
of	O
the	O
effect	O
of	O
AOP	O
is	O
that	O
control	O
flow	O
is	O
obscured	O
,	O
and	O
that	O
it	O
is	O
not	O
only	O
worse	O
than	O
the	O
much-maligned	O
GOTO	B-Application
,	O
but	O
is	O
in	O
fact	O
closely	O
analogous	O
to	O
the	O
joke	O
COME	O
FROM	O
statement	O
.	O
</s>
<s>
The	O
obliviousness	O
of	O
application	O
,	O
which	O
is	O
fundamental	O
to	O
many	O
definitions	O
of	O
AOP	O
(	O
the	O
code	O
in	O
question	O
has	O
no	O
indication	O
that	O
an	O
advice	B-Application
will	O
be	O
applied	O
,	O
which	O
is	O
specified	O
instead	O
in	O
the	O
pointcut	B-Application
)	O
,	O
means	O
that	O
the	O
advice	B-Application
is	O
not	O
visible	O
,	O
in	O
contrast	O
to	O
an	O
explicit	O
method	O
call	O
.	O
</s>
<s>
Indeed	O
,	O
the	O
pointcut	B-Application
may	O
depend	O
on	O
runtime	O
condition	O
and	O
thus	O
not	O
be	O
statically	O
deterministic	O
.	O
</s>
<s>
General	O
criticisms	O
are	O
that	O
AOP	O
purports	O
to	O
improve	O
"	O
both	O
modularity	B-Architecture
and	O
the	O
structure	O
of	O
code	O
"	O
,	O
but	O
some	O
counter	O
that	O
it	O
instead	O
undermines	O
these	O
goals	O
and	O
impedes	O
"	O
independent	O
development	O
and	O
understandability	O
of	O
programs	O
"	O
.	O
</s>
<s>
Specifically	O
,	O
quantification	O
by	O
pointcuts	B-Application
breaks	O
modularity	B-Architecture
:	O
"	O
one	O
must	O
,	O
in	O
general	O
,	O
have	O
whole-program	O
knowledge	O
to	O
reason	O
about	O
the	O
dynamic	O
execution	O
of	O
an	O
aspect-oriented	B-Architecture
program.	O
"	O
</s>
<s>
Further	O
,	O
while	O
its	O
goals	O
(	O
modularizing	O
cross-cutting	B-Application
concerns	I-Application
)	O
are	O
well	O
understood	O
,	O
its	O
actual	O
definition	O
is	O
unclear	O
and	O
not	O
clearly	O
distinguished	O
from	O
other	O
well-established	O
techniques	O
.	O
</s>
<s>
Cross-cutting	B-Application
concerns	I-Application
potentially	O
cross-cut	O
each	O
other	O
,	O
requiring	O
some	O
resolution	O
mechanism	O
,	O
such	O
as	O
ordering	O
.	O
</s>
<s>
Technical	O
criticisms	O
include	O
that	O
the	O
quantification	O
of	O
pointcuts	B-Application
(	O
defining	O
where	O
advices	O
are	O
executed	O
)	O
is	O
"	O
extremely	O
sensitive	O
to	O
changes	O
in	O
the	O
program	O
"	O
,	O
which	O
is	O
known	O
as	O
the	O
fragile	O
pointcut	B-Application
problem	O
.	O
</s>
<s>
The	O
problems	O
with	O
pointcuts	B-Application
are	O
deemed	O
intractable	O
:	O
if	O
one	O
replaces	O
the	O
quantification	O
of	O
pointcuts	B-Application
with	O
explicit	O
annotations	O
,	O
one	O
obtains	O
attribute-oriented	B-Application
programming	I-Application
instead	O
,	O
which	O
is	O
simply	O
an	O
explicit	O
subroutine	O
call	O
and	O
suffers	O
the	O
identical	O
problem	O
of	O
scattering	O
that	O
AOP	O
was	O
designed	O
to	O
solve	O
.	O
</s>
<s>
Unity	B-Application
provides	O
an	O
API	O
to	O
facilitate	O
proven	O
practices	O
in	O
core	O
areas	O
of	O
programming	O
including	O
data	O
access	O
,	O
security	O
,	O
logging	O
,	O
exception	O
handling	O
and	O
others	O
.	O
</s>
<s>
is	O
an	O
AOP	O
implementation	O
allowing	O
to	O
weave	O
the	O
aspects	O
directly	O
on	O
the	O
.net	B-Application
executable	O
files	O
.	O
</s>
