<s>
The	O
event	B-Application
calculus	I-Application
is	O
a	O
logical	O
language	O
for	O
representing	O
and	O
reasoning	O
about	O
events	O
and	O
their	O
effects	O
first	O
presented	O
by	O
Robert	O
Kowalski	O
and	O
Marek	O
Sergot	O
in	O
1986	O
.	O
</s>
<s>
Similar	O
to	O
other	O
languages	O
for	O
reasoning	O
about	O
change	O
,	O
the	O
event	B-Application
calculus	I-Application
represents	O
the	O
effects	O
of	O
actions	O
on	O
fluents	O
.	O
</s>
<s>
In	O
the	O
event	B-Application
calculus	I-Application
,	O
one	O
can	O
specify	O
the	O
value	O
of	O
fluents	O
at	O
some	O
given	O
time	O
points	O
,	O
the	O
events	O
that	O
take	O
place	O
at	O
given	O
time	O
points	O
,	O
and	O
their	O
effects	O
.	O
</s>
<s>
In	O
the	O
event	B-Application
calculus	I-Application
,	O
fluents	O
are	O
reified	O
.	O
</s>
<s>
This	O
means	O
that	O
they	O
are	O
not	O
formalized	O
by	O
means	O
of	O
predicates	B-Algorithm
but	O
by	O
means	O
of	O
functions	O
.	O
</s>
<s>
A	O
separate	O
predicate	B-Algorithm
is	O
used	O
to	O
tell	O
which	O
fluents	O
hold	O
at	O
a	O
given	O
time	O
point	O
.	O
</s>
<s>
For	O
example	O
,	O
means	O
that	O
the	O
box	O
is	O
on	O
the	O
table	O
at	O
time	O
;	O
in	O
this	O
formula	O
,	O
is	O
a	O
predicate	B-Algorithm
while	O
is	O
a	O
function	O
.	O
</s>
<s>
The	O
effects	O
of	O
events	O
are	O
given	O
using	O
the	O
predicates	B-Algorithm
and	O
.	O
</s>
<s>
Like	O
other	O
languages	O
for	O
representing	O
actions	O
,	O
the	O
event	B-Application
calculus	I-Application
formalizes	O
the	O
correct	O
evolution	O
of	O
the	O
fluent	O
via	O
formulae	O
telling	O
the	O
value	O
of	O
each	O
fluent	O
after	O
an	O
arbitrary	O
action	O
has	O
been	O
performed	O
.	O
</s>
<s>
The	O
event	B-Application
calculus	I-Application
solves	O
the	O
frame	B-Application
problem	I-Application
in	O
a	O
way	O
that	O
is	O
similar	O
to	O
the	O
successor	O
state	O
axioms	O
of	O
the	O
situation	B-Application
calculus	I-Application
:	O
a	O
fluent	O
is	O
true	O
at	O
time	O
if	O
and	O
only	O
if	O
it	O
has	O
been	O
made	O
true	O
in	O
the	O
past	O
and	O
has	O
not	O
been	O
made	O
false	O
in	O
the	O
meantime	O
.	O
</s>
<s>
The	O
predicate	B-Algorithm
,	O
stating	O
that	O
a	O
fluent	O
has	O
been	O
made	O
false	O
during	O
an	O
interval	O
,	O
can	O
be	O
axiomatized	O
,	O
or	O
simply	O
taken	O
as	O
a	O
shorthand	O
,	O
as	O
follows	O
:	O
</s>
<s>
The	O
axioms	O
above	O
relate	O
the	O
value	O
of	O
the	O
predicates	B-Algorithm
,	O
and	O
,	O
but	O
do	O
not	O
specify	O
which	O
fluents	O
are	O
known	O
to	O
be	O
true	O
and	O
which	O
events	O
actually	O
make	O
fluents	O
true	O
or	O
false	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
event	O
makes	O
the	O
fluent	O
true	O
,	O
but	O
only	O
if	O
is	O
currently	O
true	O
,	O
the	O
corresponding	O
formula	O
in	O
the	O
event	B-Application
calculus	I-Application
is	O
:	O
</s>
<s>
This	O
problem	O
can	O
be	O
solved	O
by	O
the	O
application	O
of	O
circumscription	B-Application
to	O
a	O
set	O
of	O
formulae	O
each	O
specifying	O
one	O
effect	O
of	O
one	O
event	O
:	O
</s>
<s>
This	O
fact	O
can	O
be	O
formalized	O
by	O
simply	O
circumscribing	O
the	O
predicate	B-Algorithm
in	O
the	O
formula	O
above	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
note	O
that	O
this	O
circumscription	B-Application
is	O
done	O
only	O
on	O
the	O
formulae	O
specifying	O
and	O
not	O
on	O
the	O
domain-independent	O
axioms	O
.	O
</s>
<s>
The	O
predicate	B-Algorithm
can	O
be	O
specified	O
in	O
the	O
same	O
way	O
is	O
.	O
</s>
<s>
A	O
similar	O
approach	O
can	O
be	O
taken	O
for	O
the	O
predicate	B-Algorithm
.	O
</s>
<s>
The	O
evaluation	O
of	O
this	O
predicate	B-Algorithm
can	O
be	O
enforced	O
by	O
formulae	O
specifying	O
not	O
only	O
when	O
it	O
is	O
true	O
and	O
when	O
it	O
is	O
false	O
:	O
</s>
<s>
Circumscription	B-Application
can	O
simplify	O
this	O
specification	O
,	O
as	O
only	O
necessary	O
conditions	O
can	O
be	O
specified	O
:	O
</s>
<s>
Circumscribing	O
the	O
predicate	B-Algorithm
,	O
this	O
predicate	B-Algorithm
will	O
be	O
false	O
at	O
all	O
points	O
in	O
which	O
it	O
is	O
not	O
explicitly	O
specified	O
to	O
be	O
true	O
.	O
</s>
<s>
This	O
circumscription	B-Application
has	O
to	O
be	O
done	O
separately	O
from	O
the	O
circumscription	B-Application
of	O
the	O
other	O
formulae	O
.	O
</s>
<s>
The	O
event	B-Application
calculus	I-Application
was	O
originally	O
formulated	O
as	O
a	O
set	O
of	O
Horn	B-Application
clauses	I-Application
augmented	O
with	O
negation	B-Application
as	I-Application
failure	I-Application
and	O
could	O
be	O
run	O
as	O
a	O
Prolog	B-Language
program	O
.	O
</s>
<s>
In	O
fact	O
,	O
circumscription	B-Application
is	O
one	O
of	O
the	O
several	O
semantics	O
that	O
can	O
be	O
given	O
to	O
negation	B-Application
as	I-Application
failure	I-Application
,	O
and	O
is	O
closely	O
related	O
to	O
the	O
completion	O
semantics	O
(	O
in	O
which	O
"	O
if	O
"	O
is	O
interpreted	O
as	O
"	O
if	O
and	O
only	O
if	O
"	O
see	O
logic	B-Language
programming	I-Language
)	O
.	O
</s>
<s>
The	O
original	O
event	B-Application
calculus	I-Application
paper	O
of	O
Kowalski	O
and	O
Sergot	O
focused	O
on	O
applications	O
to	O
database	O
updates	O
and	O
narratives	O
.	O
</s>
<s>
Extensions	O
of	O
the	O
event	B-Application
calculus	I-Application
can	O
also	O
formalize	O
non-deterministic	O
actions	O
,	O
concurrent	O
actions	O
,	O
actions	O
with	O
delayed	O
effects	O
,	O
gradual	O
changes	O
,	O
actions	O
with	O
duration	O
,	O
continuous	O
change	O
,	O
and	O
non-inertial	O
fluents	O
.	O
</s>
<s>
Kave	O
Eshghi	O
showed	O
how	O
the	O
event	B-Application
calculus	I-Application
can	O
be	O
used	O
for	O
planning	O
,	O
using	O
abduction	O
to	O
generate	O
hypothetical	O
events	O
in	O
abductive	B-Application
logic	I-Application
programming	I-Application
.	O
</s>
<s>
Van	O
Lambalgen	O
and	O
Hamm	O
showed	O
how	O
the	O
event	B-Application
calculus	I-Application
can	O
also	O
be	O
used	O
to	O
give	O
an	O
algorithmic	O
semantics	O
to	O
tense	O
and	O
aspect	O
in	O
natural	O
language	O
using	O
constraint	B-Application
logic	I-Application
programming	I-Application
.	O
</s>
<s>
Other	O
notable	O
extensions	O
of	O
the	O
Event	B-Application
Calculus	I-Application
include	O
Markov	O
Logic	O
Networks-based	O
,	O
probabilistic	O
,	O
epistemic	O
variants	O
and	O
their	O
combinations	O
.	O
</s>
<s>
In	O
addition	O
to	O
Prolog	B-Language
and	O
its	O
variants	O
,	O
several	O
other	O
tools	O
for	O
reasoning	O
using	O
the	O
event	B-Application
calculus	I-Application
are	O
also	O
available	O
:	O
</s>
