<s>
Action	B-Language
semantics	I-Language
is	O
a	O
framework	O
for	O
the	O
formal	B-Application
specification	I-Application
of	O
semantics	B-Application
of	I-Application
programming	I-Application
languages	I-Application
invented	O
by	O
David	O
Watt	O
and	O
Peter	O
D	O
.	O
Mosses	O
in	O
the	O
1990s	O
.	O
</s>
<s>
It	O
is	O
a	O
mixture	O
of	O
denotational	B-Application
,	O
operational	O
and	O
algebraic	B-Application
semantics	I-Application
.	O
</s>
<s>
Action	B-Language
Semantics	I-Language
aims	O
to	O
be	O
pragmatic	O
.	O
</s>
<s>
Action-Semantic	B-Language
Descriptions	I-Language
(	O
ASDs	O
)	O
are	O
designed	O
to	O
scale	O
up	O
to	O
handle	O
realistic	O
programming	O
languages	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
the	O
typical	O
case	O
when	O
extending	O
denotational	B-Application
or	O
operational	O
semantics	B-Application
,	O
which	O
may	O
require	O
reformulation	O
of	O
the	O
entire	O
description	O
.	O
</s>
<s>
The	O
Action	B-Language
Semantics	I-Language
framework	O
was	O
originally	O
developed	O
at	O
the	O
University	O
of	O
Aarhus	O
and	O
the	O
University	O
of	O
Glasgow	O
.	O
</s>
<s>
An	O
important	O
part	O
of	O
action	B-Language
semantics	I-Language
that	O
gives	O
it	O
a	O
modularity	O
not	O
seen	O
in	O
previous	O
programming	B-Application
language	I-Application
semantics	I-Application
is	O
the	O
use	O
of	O
first-order	O
semantic	O
entities	O
.	O
</s>
<s>
First-order	O
refers	O
to	O
how	O
,	O
unlike	O
in	O
denotational	B-Application
semantics	I-Application
,	O
where	O
a	O
semantic	O
function	O
can	O
be	O
applied	O
to	O
another	O
semantic	O
function	O
,	O
in	O
action	B-Language
semantics	I-Language
,	O
a	O
semantic	O
entity	O
cannot	O
be	O
applied	O
to	O
another	O
semantic	O
entity	O
of	O
its	O
kind	O
.	O
</s>
<s>
Furthermore	O
,	O
the	O
semantic	O
entities	O
utilized	O
by	O
action	B-Language
semantics	I-Language
broaden	O
the	O
framework	O
’s	O
ability	O
to	O
describe	O
a	O
programming	O
language	O
’s	O
constructs	O
by	O
serving	O
to	O
denote	O
both	O
program	O
behavior	O
that	O
is	O
independent	O
of	O
any	O
particular	O
implementation	O
and	O
the	O
way	O
in	O
which	O
parts	O
of	O
a	O
program	O
influence	O
the	O
overall	O
performance	O
of	O
the	O
whole	O
.	O
</s>
<s>
The	O
appropriately	O
named	O
action	O
notation	O
is	O
employed	O
to	O
express	O
the	O
three	O
types	O
of	O
semantic	O
entities	O
found	O
in	O
action	B-Language
semantics	I-Language
:	O
actions	O
,	O
data	O
,	O
and	O
yielders	O
.	O
</s>
<s>
Action	O
entities	O
can	O
directly	O
represent	O
programs’	O
semantics	B-Application
by	O
describing	O
possible	O
program	O
behaviors	O
or	O
represent	O
,	O
in	O
a	O
more	O
indirect	O
way	O
,	O
the	O
impact	O
that	O
individual	O
pieces	O
of	O
a	O
program	O
,	O
like	O
statements	O
or	O
expressions	O
,	O
have	O
on	O
the	O
semantics	B-Application
of	O
the	O
program	O
as	O
a	O
whole	O
.	O
</s>
<s>
This	O
is	O
the	O
technique	O
by	O
which	O
action	B-Language
semantics	I-Language
represents	O
the	O
declaring	O
and	O
invoking	O
of	O
subprograms	O
.	O
</s>
<s>
Action	B-Language
semantics	I-Language
embodies	O
a	O
level	O
of	O
abstraction	O
that	O
increases	O
its	O
comprehensibility	O
.	O
</s>
<s>
The	O
specifics	O
of	O
the	O
control	O
and	O
data	O
flows	O
that	O
an	O
action	O
involves	O
are	O
implicitly	O
incorporated	O
in	O
the	O
action	O
,	O
as	O
opposed	O
to	O
being	O
explicitly	O
expressed	O
as	O
the	O
details	O
of	O
semantic	O
functions	O
are	O
in	O
denotational	B-Application
semantics	I-Application
.	O
</s>
<s>
Program	O
phrases	O
are	O
mapped	O
to	O
actions	O
when	O
constructing	O
a	O
definition	O
of	O
a	O
programming	O
language	O
’s	O
meaning	O
in	O
action	B-Language
semantics	I-Language
.	O
</s>
<s>
The	O
programming	O
language	O
specification	B-Application
generated	O
from	O
the	O
application	O
of	O
action	B-Language
semantics	I-Language
can	O
be	O
broken	O
down	O
into	O
a	O
lower	O
level	O
(	O
microsemantics	O
)	O
and	O
an	O
upper	O
level	O
(	O
macrosemantics	O
)	O
.	O
</s>
