<s>
A	O
spoken	B-General_Concept
dialog	I-General_Concept
system	I-General_Concept
(	O
SDS	O
)	O
is	O
a	O
computer	O
system	O
able	O
to	O
converse	O
with	O
a	O
human	O
with	O
voice	O
.	O
</s>
<s>
It	O
has	O
two	O
essential	O
components	O
that	O
do	O
not	O
exist	O
in	O
a	O
written	O
text	O
dialog	B-General_Concept
system	I-General_Concept
:	O
a	O
speech	B-Application
recognizer	I-Application
and	O
a	O
text-to-speech	B-Application
module	O
(	O
written	O
text	O
dialog	B-General_Concept
systems	I-General_Concept
usually	O
use	O
other	O
input	O
systems	O
provided	O
by	O
an	O
OS	O
)	O
.	O
</s>
<s>
An	O
automatic	B-Application
speech	I-Application
recognizer	I-Application
(	O
ASR	O
)	O
decodes	O
speech	O
into	O
text	O
.	O
</s>
<s>
Natural	B-General_Concept
language	I-General_Concept
understanding	I-General_Concept
transforms	O
a	O
recognition	O
into	O
a	O
concept	O
structure	O
that	O
can	O
drive	O
system	O
behavior	O
.	O
</s>
<s>
The	O
dialog	B-General_Concept
manager	I-General_Concept
controls	O
turn-by-turn	O
behavior	O
.	O
</s>
<s>
A	O
simple	O
dialog	B-General_Concept
system	I-General_Concept
may	O
ask	O
the	O
user	O
questions	O
then	O
act	O
on	O
the	O
response	O
.	O
</s>
<s>
Such	O
directed	O
dialog	B-General_Concept
systems	I-General_Concept
use	O
a	O
tree-like	O
structure	O
for	O
control	O
;	O
frame	O
-	O
(	O
or	O
form	O
-	O
)	O
based	O
systems	O
allow	O
for	O
some	O
user	O
initiative	O
and	O
accommodate	O
different	O
styles	O
of	O
interaction	O
.	O
</s>
<s>
More	O
sophisticated	O
dialog	B-General_Concept
managers	I-General_Concept
incorporate	O
mechanisms	O
for	O
dealing	O
with	O
misunderstandings	O
and	O
clarification	O
.	O
</s>
<s>
The	O
domain	O
reasoner	O
,	O
together	O
with	O
the	O
dialog	B-General_Concept
manager	I-General_Concept
,	O
maintain	O
the	O
context	O
of	O
interaction	O
and	O
allows	O
the	O
system	O
to	O
reflect	O
some	O
human	O
conversational	O
abilities	O
(	O
for	O
example	O
using	O
anaphora	O
)	O
.	O
</s>
<s>
Response	O
generation	O
is	O
similar	O
to	O
text-based	O
natural	B-General_Concept
language	I-General_Concept
generation	I-General_Concept
,	O
but	O
takes	O
into	O
account	O
the	O
needs	O
of	O
spoken	O
communication	O
.	O
</s>
<s>
Text-to-speech	B-Application
synthesis	O
(	O
TTS	O
)	O
realizes	O
an	O
intended	O
utterance	O
as	O
speech	O
.	O
</s>
<s>
Spoken	B-General_Concept
dialog	I-General_Concept
systems	I-General_Concept
vary	O
in	O
their	O
complexity	O
.	O
</s>
<s>
Directed	O
dialog	B-General_Concept
systems	I-General_Concept
are	O
very	O
simple	O
and	O
require	O
that	O
the	O
developer	O
create	O
a	O
graph	O
(	O
typically	O
a	O
tree	O
)	O
that	O
manages	O
the	O
task	O
but	O
may	O
not	O
correspond	O
to	O
the	O
needs	O
of	O
the	O
user	O
.	O
</s>
<s>
Problem-solving	O
dialog	B-General_Concept
systems	I-General_Concept
may	O
allow	O
human	O
users	O
to	O
engage	O
in	O
a	O
number	O
of	O
different	O
activities	O
that	O
may	O
include	O
information	O
access	O
,	O
plan	O
construction	O
and	O
possible	O
execution	O
of	O
the	O
latter	O
.	O
</s>
<s>
Pionieers	O
in	O
dialogue	B-General_Concept
systems	I-General_Concept
are	O
companies	O
like	O
AT&T	O
(	O
with	O
its	O
speech	B-Application
recognizer	I-Application
system	O
in	O
the	O
Seventies	O
)	O
and	O
CSELT	O
laboratories	O
,	O
that	O
led	O
some	O
European	O
research	O
projects	O
during	O
the	O
Eighties	O
(	O
e.g.	O
</s>
