<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
formal	B-Application
specifications	I-Application
are	O
mathematically	O
based	O
techniques	O
whose	O
purpose	O
are	O
to	O
help	O
with	O
the	O
implementation	O
of	O
systems	O
and	O
software	O
.	O
</s>
<s>
These	O
specifications	B-Application
are	O
formal	O
in	O
the	O
sense	O
that	O
they	O
have	O
a	O
syntax	O
,	O
their	O
semantics	O
fall	O
within	O
one	O
domain	O
,	O
and	O
they	O
are	O
able	O
to	O
be	O
used	O
to	O
infer	O
useful	O
information	O
.	O
</s>
<s>
Formal	B-Application
specifications	I-Application
are	O
one	O
such	O
way	O
to	O
achieve	O
this	O
in	O
software	B-General_Concept
engineering	I-General_Concept
reliability	O
as	O
once	O
predicted	O
.	O
</s>
<s>
Given	O
such	O
a	O
specification	B-Application
,	O
it	O
is	O
possible	O
to	O
use	O
formal	O
verification	O
techniques	O
to	O
demonstrate	O
that	O
a	O
system	O
design	O
is	O
correct	O
with	O
respect	O
to	O
its	O
specification	B-Application
.	O
</s>
<s>
Another	O
approach	O
is	O
to	O
use	O
probably	O
correct	O
refinement	O
steps	O
to	O
transform	O
a	O
specification	B-Application
into	O
a	O
design	O
,	O
which	O
is	O
ultimately	O
transformed	O
into	O
an	O
implementation	O
that	O
is	O
correct	O
by	O
construction	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
note	O
that	O
a	O
formal	B-Application
specification	I-Application
is	O
not	O
an	O
implementation	O
,	O
but	O
rather	O
it	O
may	O
be	O
used	O
to	O
develop	O
an	O
implementation	O
.	O
</s>
<s>
Formal	B-Application
specifications	I-Application
describe	O
what	O
a	O
system	O
should	O
do	O
,	O
not	O
how	O
the	O
system	O
should	O
do	O
it	O
.	O
</s>
<s>
A	O
good	O
specification	B-Application
will	O
have	O
:	O
</s>
<s>
One	O
of	O
the	O
main	O
reasons	O
there	O
is	O
interest	O
in	O
formal	B-Application
specifications	I-Application
is	O
that	O
they	O
will	O
provide	O
an	O
ability	O
to	O
perform	O
proofs	O
on	O
software	O
implementations	O
.	O
</s>
<s>
These	O
proofs	O
may	O
be	O
used	O
to	O
validate	B-Application
a	O
specification	B-Application
,	O
verify	O
correctness	O
of	O
design	O
,	O
or	O
to	O
prove	O
that	O
a	O
program	O
satisfies	O
a	O
specification	B-Application
.	O
</s>
<s>
It	O
can	O
only	O
ever	O
be	O
“	O
correct	O
with	O
respect	O
to	O
a	O
given	O
specification	B-Application
”	O
.	O
</s>
<s>
Whether	O
the	O
formal	B-Application
specification	I-Application
correctly	O
describes	O
the	O
problem	O
to	O
be	O
solved	O
is	O
a	O
separate	O
issue	O
.	O
</s>
<s>
It	O
is	O
also	O
a	O
difficult	O
issue	O
to	O
address	O
since	O
it	O
ultimately	O
concerns	O
the	O
problem	O
constructing	O
abstracted	O
formal	O
representations	O
of	O
an	O
informal	O
concrete	O
problem	B-General_Concept
domain	I-General_Concept
,	O
and	O
such	O
an	O
abstraction	O
step	O
is	O
not	O
amenable	O
to	O
formal	O
proof	O
.	O
</s>
<s>
However	O
,	O
it	O
is	O
possible	O
to	O
validate	B-Application
a	O
specification	B-Application
by	O
proving	O
“	O
challenge	O
”	O
theorems	O
concerning	O
properties	O
that	O
the	O
specification	B-Application
is	O
expected	O
to	O
exhibit	O
.	O
</s>
<s>
If	O
correct	O
,	O
these	O
theorems	O
reinforce	O
the	O
specifier	O
's	O
understanding	O
of	O
the	O
specification	B-Application
and	O
its	O
relationship	O
with	O
the	O
underlying	O
problem	B-General_Concept
domain	I-General_Concept
.	O
</s>
<s>
If	O
not	O
,	O
the	O
specification	B-Application
probably	O
needs	O
to	O
be	O
changed	O
to	O
better	O
reflect	O
the	O
domain	O
understanding	O
of	O
those	O
involved	O
with	O
producing	O
(	O
and	O
implementing	O
)	O
the	O
specification	B-Application
.	O
</s>
<s>
Formal	B-Architecture
methods	I-Architecture
of	O
software	O
development	O
are	O
not	O
widely	O
used	O
in	O
industry	O
.	O
</s>
<s>
Doing	O
a	O
formal	B-Application
specification	I-Application
of	O
the	O
whole	O
system	O
up	O
front	O
is	O
often	O
perceived	O
as	O
being	O
the	O
opposite	O
of	O
flexible	O
.	O
</s>
<s>
Formal	B-Application
specification	I-Application
techniques	O
have	O
existed	O
in	O
various	O
domains	O
and	O
on	O
various	O
scales	O
for	O
quite	O
some	O
time	O
.	O
</s>
<s>
Implementations	O
of	O
formal	B-Application
specifications	I-Application
will	O
differ	O
depending	O
on	O
what	O
kind	O
of	O
system	O
they	O
are	O
attempting	O
to	O
model	O
,	O
how	O
they	O
are	O
applied	O
and	O
at	O
what	O
point	O
in	O
the	O
software	O
life	O
cycle	O
they	O
have	O
been	O
introduced	O
.	O
</s>
<s>
These	O
types	O
of	O
models	O
can	O
be	O
categorized	O
into	O
the	O
following	O
specification	B-Application
paradigms	O
:	O
</s>
<s>
In	O
addition	O
to	O
the	O
above	O
paradigms	O
,	O
there	O
are	O
ways	O
to	O
apply	O
certain	O
heuristics	O
to	O
help	O
improve	O
the	O
creation	O
of	O
these	O
specifications	B-Application
.	O
</s>
<s>
The	O
paper	O
referenced	O
here	O
best	O
discusses	O
heuristics	O
to	O
use	O
when	O
designing	O
a	O
specification	B-Application
.	O
</s>
<s>
They	O
do	O
so	O
by	O
applying	O
a	O
divide-and-conquer	B-Algorithm
approach	O
.	O
</s>
<s>
The	O
Z	B-Language
notation	I-Language
is	O
an	O
example	O
of	O
a	O
leading	O
formal	B-Application
specification	I-Application
language	I-Application
.	O
</s>
<s>
Others	O
include	O
the	O
Specification	B-Application
Language	I-Application
(	O
VDM-SL	B-Application
)	O
of	O
the	O
Vienna	B-Application
Development	I-Application
Method	I-Application
and	O
the	O
Abstract	B-Application
Machine	I-Application
Notation	I-Application
(	O
AMN	O
)	O
of	O
the	O
B-Method	B-Application
.	O
</s>
<s>
In	O
the	O
Web	O
services	O
area	O
,	O
formal	B-Application
specification	I-Application
is	O
often	O
used	O
to	O
describe	O
non-functional	O
properties	O
(	O
Web	O
services	O
quality	O
of	O
service	O
)	O
.	O
</s>
