<s>
Subareas	O
include	O
the	O
coupling	B-Application
of	O
classes	O
,	O
interfaces	B-Application
,	O
data	O
,	O
and	O
services	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
is	O
the	O
opposite	O
of	O
tight	B-Application
coupling	I-Application
.	O
</s>
<s>
Components	O
in	O
a	O
loosely	B-Application
coupled	I-Application
system	O
can	O
be	O
replaced	O
with	O
alternative	O
implementations	O
that	O
provide	O
the	O
same	O
services	O
.	O
</s>
<s>
Components	O
in	O
a	O
loosely	B-Application
coupled	I-Application
system	O
are	O
less	O
constrained	O
to	O
the	O
same	O
platform	O
,	O
language	O
,	O
operating	B-General_Concept
system	I-General_Concept
,	O
or	O
build	O
environment	O
.	O
</s>
<s>
Data	B-Architecture
replication	I-Architecture
across	O
different	O
systems	O
provides	O
loose	B-Application
coupling	I-Application
(	O
in	O
availability	O
)	O
,	O
but	O
creates	O
issues	O
in	O
maintaining	O
consistency	B-General_Concept
(	O
data	B-General_Concept
synchronization	I-General_Concept
)	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
in	O
broader	O
distributed	B-Architecture
system	I-Architecture
design	O
is	O
achieved	O
by	O
the	O
use	O
of	O
transactions	O
,	O
queues	O
provided	O
by	O
message-oriented	B-Application
middleware	I-Application
,	O
and	O
interoperability	O
standards	O
.	O
</s>
<s>
Four	O
types	O
of	O
autonomy	O
,	O
which	O
promote	O
loose	B-Application
coupling	I-Application
,	O
are	O
:	O
reference	O
autonomy	O
,	O
time	O
autonomy	O
,	O
format	O
autonomy	O
,	O
and	O
platform	O
autonomy	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
is	O
an	O
architectural	O
principle	O
and	O
design	O
goal	O
in	O
service-oriented	O
architectures	O
;	O
eleven	O
forms	O
of	O
loose	B-Application
coupling	I-Application
and	O
their	O
tight	B-Application
coupling	I-Application
counterparts	O
are	O
listed	O
in	O
:	O
</s>
<s>
simple	O
common	O
types	O
only	O
in	O
data	B-Application
model	I-Application
,	O
</s>
<s>
Enterprise	B-Application
Service	I-Application
Bus	I-Application
(	O
ESB	O
)	O
middleware	O
was	O
invented	O
to	O
achieve	O
loose	B-Application
coupling	I-Application
in	O
multiple	O
dimensions	O
;	O
however	O
,	O
overengineered	O
and	O
mispositioned	O
ESBs	O
can	O
also	O
have	O
the	O
contrary	O
effect	O
and	O
create	O
undesired	O
tight	B-Application
coupling	I-Application
and	O
a	O
central	O
architectural	O
hotspot	O
.	O
</s>
<s>
Event-driven	B-Application
architecture	I-Application
also	O
aims	O
at	O
promoting	O
loose	B-Application
coupling	I-Application
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
of	O
interfaces	B-Application
can	O
be	O
enhanced	O
by	O
publishing	O
data	O
in	O
a	O
standard	O
format	O
(	O
such	O
as	O
XML	B-Protocol
or	O
JSON	B-General_Concept
)	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
between	O
program	O
components	O
can	O
be	O
enhanced	O
by	O
using	O
standard	O
data	O
types	O
in	O
parameters	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
of	O
services	O
can	O
be	O
enhanced	O
by	O
reducing	O
the	O
information	O
passed	O
into	O
a	O
service	O
to	O
the	O
key	O
data	O
.	O
</s>
<s>
Coupling	B-Application
refers	O
to	O
the	O
degree	O
of	O
direct	O
knowledge	O
that	O
one	O
component	O
has	O
of	O
another	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
in	O
computing	O
is	O
interpreted	O
as	O
encapsulation	B-Application
vs.	O
non-encapsulation	O
.	O
</s>
<s>
An	O
example	O
of	O
tight	B-Application
coupling	I-Application
occurs	O
when	O
a	O
dependent	O
class	O
contains	O
a	O
pointer	O
directly	O
to	O
a	O
concrete	O
class	O
which	O
provides	O
the	O
required	O
behavior	O
.	O
</s>
<s>
The	O
dependency	B-Application
cannot	O
be	O
substituted	O
,	O
or	O
its	O
"	O
signature	O
"	O
changed	O
,	O
without	O
requiring	O
a	O
change	O
to	O
the	O
dependent	O
class	O
.	O
</s>
<s>
Loose	B-Application
coupling	I-Application
occurs	O
when	O
the	O
dependent	O
class	O
contains	O
a	O
pointer	O
only	O
to	O
an	O
interface	O
,	O
which	O
can	O
then	O
be	O
implemented	O
by	O
one	O
or	O
many	O
concrete	O
classes	O
.	O
</s>
<s>
This	O
is	O
known	O
as	O
dependency	B-Application
inversion	O
.	O
</s>
<s>
The	O
dependent	O
class	O
's	O
dependency	B-Application
is	O
to	O
a	O
"	O
contract	O
"	O
specified	O
by	O
the	O
interface	O
;	O
a	O
defined	O
list	O
of	O
methods	O
and/or	O
properties	O
that	O
implementing	O
classes	O
must	O
provide	O
.	O
</s>
<s>
Any	O
class	O
that	O
implements	O
the	O
interface	O
can	O
thus	O
satisfy	O
the	O
dependency	B-Application
of	O
a	O
dependent	O
class	O
without	O
having	O
to	O
change	O
the	O
class	O
.	O
</s>
<s>
This	O
allows	O
for	O
extensibility	O
in	O
software	O
design	O
;	O
a	O
new	O
class	O
implementing	O
an	O
interface	O
can	O
be	O
written	O
to	O
replace	O
a	O
current	O
dependency	B-Application
in	O
some	O
or	O
all	O
situations	O
,	O
without	O
requiring	O
a	O
change	O
to	O
the	O
dependent	O
class	O
;	O
the	O
new	O
and	O
old	O
classes	O
can	O
be	O
interchanged	O
freely	O
.	O
</s>
<s>
Strong	O
coupling	B-Application
does	O
not	O
allow	O
this	O
.	O
</s>
<s>
This	O
is	O
a	O
UML	B-Language
diagram	I-Language
illustrating	O
an	O
example	O
of	O
loose	B-Application
coupling	I-Application
between	O
a	O
dependent	O
class	O
and	O
a	O
set	O
of	O
concrete	O
classes	O
,	O
which	O
provide	O
the	O
required	O
behavior	O
:	O
</s>
<s>
For	O
comparison	O
,	O
this	O
diagram	O
illustrates	O
the	O
alternative	O
design	O
with	O
strong	O
coupling	B-Application
between	O
the	O
dependent	O
class	O
and	O
a	O
provider	O
:	O
</s>
<s>
Computer	O
programming	O
languages	O
having	O
notions	O
of	O
either	O
functions	O
as	O
the	O
core	O
module	O
(	O
see	O
Functional	B-Language
programming	I-Language
)	O
or	O
functions	O
as	O
objects	O
provide	O
excellent	O
examples	O
of	O
loosely	B-Application
coupled	I-Application
programming	O
.	O
</s>
<s>
Functional	B-Language
languages	I-Language
have	O
patterns	O
of	O
Continuations	O
,	O
Closure	B-Language
,	O
or	O
generators	O
.	O
</s>
<s>
See	O
Clojure	B-Language
and	O
Lisp	B-Language
as	O
examples	O
of	O
function	O
programming	O
languages	O
.	O
</s>
<s>
Object-oriented	O
languages	O
like	O
Smalltalk	B-Application
and	O
Ruby	B-Language
have	O
code	O
blocks	O
,	O
whereas	O
Eiffel	B-Language
has	O
agents	O
.	O
</s>
<s>
See	O
First-class	B-Application
function	I-Application
for	O
further	O
insight	O
into	O
functions	O
as	O
objects	O
,	O
which	O
qualifies	O
as	O
one	O
form	O
of	O
first-class	B-Application
function	I-Application
.	O
</s>
<s>
The	O
decoupling	O
or	O
loose	B-Application
coupling	I-Application
is	O
immediately	O
apparent	O
.	O
</s>
<s>
Again	O
,	O
the	O
loose	B-Application
coupling	I-Application
or	O
decoupled	O
nature	O
of	O
this	O
functional	O
object	O
is	O
apparent	O
.	O
</s>
<s>
This	O
level	O
of	O
indirection	O
is	O
what	O
makes	O
function	O
objects	O
an	O
excellent	O
technology	O
for	O
achieving	O
loosely	B-Application
coupled	I-Application
programs	O
.	O
</s>
<s>
The	O
degree	O
of	O
the	O
loose	B-Application
coupling	I-Application
can	O
be	O
measured	O
by	O
noting	O
the	O
number	O
of	O
changes	O
in	O
data	O
elements	O
that	O
could	O
occur	O
in	O
the	O
sending	O
or	O
receiving	O
systems	O
and	O
determining	O
if	O
the	O
computers	O
would	O
still	O
continue	O
communicating	O
correctly	O
.	O
</s>
