<s>
A	O
specification	B-Application
language	I-Application
is	O
a	O
formal	O
language	O
in	O
computer	B-General_Concept
science	I-General_Concept
used	O
during	O
systems	O
analysis	O
,	O
requirements	O
analysis	O
,	O
and	O
systems	O
design	O
to	O
describe	O
a	O
system	O
at	O
a	O
much	O
higher	O
level	O
than	O
a	O
programming	O
language	O
,	O
which	O
is	O
used	O
to	O
produce	O
the	O
executable	O
code	O
for	O
a	O
system	O
.	O
</s>
<s>
Specification	B-Application
languages	I-Application
are	O
generally	O
not	O
directly	O
executed	O
.	O
</s>
<s>
Indeed	O
,	O
it	O
is	O
considered	O
as	O
an	O
error	O
if	O
a	O
requirement	O
specification	B-Application
is	O
cluttered	O
with	O
unnecessary	O
implementation	O
detail	O
.	O
</s>
<s>
A	O
common	O
fundamental	O
assumption	O
of	O
many	O
specification	B-Application
approaches	O
is	O
that	O
programs	O
are	O
modelled	O
as	O
algebraic	O
or	O
model-theoretic	O
structures	O
that	O
include	O
a	O
collection	O
of	O
sets	O
of	O
data	O
values	O
together	O
with	O
functions	O
over	O
those	O
sets	O
.	O
</s>
<s>
In	O
the	O
property-oriented	O
approach	O
to	O
specification	B-Application
(	O
taken	O
e.g.	O
</s>
<s>
by	O
CASL	B-Language
)	O
,	O
specifications	B-Application
of	O
programs	O
consist	O
mainly	O
of	O
logical	O
axioms	B-Algorithm
,	O
usually	O
in	O
a	O
logical	O
system	O
in	O
which	O
equality	O
has	O
a	O
prominent	O
role	O
,	O
describing	O
the	O
properties	O
that	O
the	O
functions	O
are	O
required	O
to	O
satisfy	O
—	O
often	O
just	O
by	O
their	O
interrelationship	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
so-called	O
model-oriented	B-Application
specification	I-Application
in	O
frameworks	O
like	O
VDM	B-Application
and	O
Z	B-Language
,	O
which	O
consist	O
of	O
a	O
simple	O
realization	O
of	O
the	O
required	O
behaviour	O
.	O
</s>
<s>
Specifications	B-Application
must	O
be	O
subject	O
to	O
a	O
process	O
of	O
refinement	O
(	O
the	O
filling-in	O
of	O
implementation	O
detail	O
)	O
before	O
they	O
can	O
actually	O
be	O
implemented	O
.	O
</s>
<s>
The	O
result	O
of	O
such	O
a	O
refinement	O
process	O
is	O
an	O
executable	O
algorithm	O
,	O
which	O
is	O
either	O
formulated	O
in	O
a	O
programming	O
language	O
,	O
or	O
in	O
an	O
executable	O
subset	O
of	O
the	O
specification	B-Application
language	I-Application
at	O
hand	O
.	O
</s>
<s>
For	O
example	O
,	O
Hartmann	B-Operating_System
pipelines	I-Operating_System
,	O
when	O
properly	O
applied	O
,	O
may	O
be	O
considered	O
a	O
dataflow	B-Application
specification	B-Application
which	O
is	O
directly	O
executable	O
.	O
</s>
<s>
Another	O
example	O
is	O
the	O
actor	B-Application
model	I-Application
which	O
has	O
no	O
specific	O
application	O
content	O
and	O
must	O
be	O
specialized	O
to	O
be	O
executable	O
.	O
</s>
<s>
An	O
important	O
use	O
of	O
specification	B-Application
languages	I-Application
is	O
enabling	O
the	O
creation	O
of	O
proofs	O
of	O
program	O
correctness	O
(	O
see	O
theorem	B-Application
prover	I-Application
)	O
.	O
</s>
