Corpus-Based Information Presentation for 
a Spoken Public Transport Information System* 
M.M.M. Rats and R.J. van Vark and J.P.M. de Vreught 
Knowledge Based Systems 
Technical Computer Science 
Delft University of Technology 
alparon@kgs.twi.tudelft.nl 
Abstract 
The Alparon project aims to improve Vxos, 
Openbaar Vervoer Reisinformatie's (OVa) 
automated speech processing system for 
public transport information, by using a 
corpus-based approach. The shortcomings 
of the current system have been investi- 
gated, and a study is made of how dialogues 
in the OVR domain usually occur between 
a human operator and a client. While cen- 
tering our attention on the presentation of 
information by the Automated Speech Pro- 
cessing (ASP) system, we describe the im- 
plications of this corpus-based approach on 
the implementation of our prototype. 
1 Introduction 
The Alparon research group in Delft aims to im- 
prove Automated Speech Processing (ASP) systems 
for information retrieval and information storing di- 
alogues. The current focus is on dialogue manage- 
ment for a research project of Openbaar Vervoer 
Reisinformatie (OVR) (Vark et al., 1996). OVR 
provides information about Dutch public transport 
systems, ranging from local bus services to long dis- 
tance trains. They are developing an ASP system, 
called VIos, to automate part of its dialogues held 
at its call centres. 
Although the second version of VIos is imple- 
mented, it is far from perfect. After conducting 
user-appreciation studies it was clear that the next 
version of VIos should act more human like. 
This is the reason why we will take the human 
operator as the source of inspiration for improve- 
ment. The proposals that we will put foreward in 
this paper will be based on a study of about 100 
human-human OVa-dialogues selected from a cor- 
pus of 5205 telephone conversations recorded at the 
This work is funded by OVP~ and Senter. 
call centers of OVa. The pilot corpus consists of di- 
alogues that concern the exchange of train informa- 
tion only. 
OVR dialogues proceed in a specific way: first 
greetings are exchanged, then the client formulates 
his query, next the operator gives the desired infor- 
mation, and finally both parties say goodbye to each 
other. In this paper, we will concentrate on the im- 
proving the presentation of the travel scheme. 
We can roughly distinguish three different situa- 
tions: the standard situation where everything runs 
smoothly, the situation where there is a repair op- 
eration by either the client or the operator, and the 
situation where a topic shift occurs. In our proto- 
type, the dialogue manager and the text generator 
will collaborate to handle these situations. Since the 
dialogue manager has knowledge concerning known 
and new information, it can instruct the text gener- 
ator to present the text in a natural way. 
In the next section, we will discuss related work. 
Then, we will describe in detail how information is 
presented in VIos and in the OVa corpus. Next, 
we will present the strategies an ASP system has to 
follow if such a system is to present information in a 
sensible manner. In the last section, we will describe 
future research. 
2 Related Work 
VIos is a Dutch version of the train timetable in- 
formation system developed by Philips Aachen for 
the Deutsche Bundesbahn (Aust and Oerder, 1995; 
Aust et al., 1995). It was developed within the Eu- 
ropean LE-MLAP project MAIS (Strik et al., 1996), 
the aim of which was to make a Dutch and French 
version of the Philips system. 
A related European research project was the LE- 
MLAP project RAILTEL (Bennacef et al., 1996) 
which strived to develop prototype telephone ser- 
vices for access to train travel information. Pro- 
totype systems are being developed for France 
106 
Figure 1: A VIOS presentation of a train connection 
V: I have found the following connection. 
Departure from Delft at twenty hours forty-two, arrival at 
Rotterdam CS at twenty hours fifty-six, there change to 
Utrecht CS, departure at twenty-one hours seven, arrival in 
Utrecht CS at twenty-one hours forty-three. 
Do you want me to repeat the connection again? 
V: Ik heb de volgende verbinding gevonden. 
Vertrek vanuit Delft om twintig uur twee~nveertig, 
aankomst in Rotterdam CS om twintig uur zesenvijftig, 
daar overstappen naar Utrecht CS, vertrek om eenentwintig 
uur zeven, aankomst in Utrecht CS om eenentwintig uur 
drie~nveertig. 
Wilt u dat ik de verbinding nog eens herhaal? 
(LIMSI), Italy (CSELT), and the U.K. (CCIR). 
The successor of these projects is the European 
project ARISE, which aims to improve the previous 
versions of the different systems. OVR is a partner 
in both MAIS and ARISE. 
Besides Alparon several other universities and 
companies in the Netherlands are working to im- 
prove VIos. Most of them are working in the Ovls 
project (Bores et al., 1995), which aims to develop 
the next version of VIOS for the Dutch context. In 
the Alparon project, we are allowed to try and test 
out new ideas beyond this next version. 
Our work is also inspired by other related research 
projects. One of them is the TRAINS project (Allen 
et al., 1995), that tries to build an interactive plan- 
ning assistant that helps a user to construct and 
monitor plans concerning a railroad freight system. 
Another related project is described in (Carenini 
et al., 1994). They have developed a system that 
uses text planning and user modelling techniques to 
generate natural language descriptions of migraine, 
its symptoms, triggering factors and prescriptions. 
The system is capable of handling follow-up ques- 
tions requesting further information, and generating 
responses in context of previously supplied informa- 
tion. In (Cawsey, 1993) the EDGE system is de- 
scribed, which is able to plan explanations which 
allow interactions with the user. 
For text generation, we found useful ideas in (Pre- 
vost, 1996), where an architecture is described for 
the generation of spoken text with contextually ap- 
propriate intonation. The schema approach (McK- 
eown, 1985), and the systems DYD (Deemter and 
Odijk, 1995), and GoalGetter (Klabbers et al., 1997) 
were inspiring too. 
3 Information presentation in VIos 
In VIos, the travel plan is presented using templates 
filled with specific stations and times. The station 
names and times have a disambiguated form, always 
resulting in a full and uniquely identifying descrip- 
tion. The templates and the words for stations and 
times are prerecorded and their accoustic represen- 
tations are concatenated to form complete sentences. 
107 
Together these sentences form a monologue. No in- 
terruptions by the caller are possible (see figure 1). 
The architecture of VIOS is such that the dia- 
logue management component and the text gener- 
ating component work in sequential order. When 
the travel scheme has been determined, the dialogue 
manager sends the entire scheme to the text genera- 
tor. This component communicates the plan to the 
caller. During the presentation process, the system 
stops listening. So, no feedback from the user to the 
system is possible. 
Appreciation studies have shown that the VIos 
presentation of information is far from ideal for the 
following reasons (Blasband, 1997; Manintveld and 
Rothkrantz, 1997; Peters and Kock, 1997): 
All information is given at once. It would 
be more convenient for the caller if the sys- 
tem would provide the information in smaller 
chunks. 
• The caller is not able to interrupt when he does 
not comprehend the given information. 
The use of full names for stations is very unnat- 
ural and confusing, especially when the caller 
has used other descriptions to introduce them. 
The system makes the caller feel hunted in pro- 
cessing and copying down the information since 
it speaks too fast. 
The information is spoken in an unnatural way. 
The concatenated phrases exhibit differences in 
speech tempo and loudness. Since they miss a 
natural intonation pattern, they are awkward 
to understand. 
In this paper, we will only work towards a so- 
lution for the first two problems. The next three 
items will be left for further research. We will take 
the human-human dialogues as an example. This 
choice is dictated by our comprehensive appreciation 
study, where 500 respondents were asked to call dif- 
ferent Wizard of Oz simulation systems, VIOS, and a 
Figure 2: An information phase of an OVR dialogue 
C: ik wilde graag weten 
als ik morgen ore: morgenochtend om negen uur \[u:h\] op de 
Lelylaan in Amsterdam moet zijn 
hoe laat moet ik vanuit Hilversum vertrekken dan? 
h dat wordt\[u:h\] acht uur negentien vertrekken uit Hilversum 
C: acht uur ja 
I: en dan overstappen Amsterdam 
C: \[u:h\] ja 
h vertrek Amsterdam acht vijfenvijftig 
C: acht vijfenvijftig 
h komt u negen nul drie aan Amsterdam Lelylaan 
C: ok6 
dus acht uur negentlen vertrekken 
ok6 
hartstikke bedankt 
C: I would like to know 
if I have to be tomorrow at: tomorrow morning at nine 
o'clock \[u:h\] at the Lelylaan in Amsterdam 
~t what time do I have to leave from Hilversum? 
h that will be\[u:h\] depart from Hilversum at eight hours 
nineteen 
C: eight hours yes 
h and then change Amsterdam 
C: \[u:h\] yes 
I: departure Amsterdam eight fifty-five 
C: eight fifty-five 
h will arrive at Amsterdam Lelylaan at nine o three 
C: okay 
so depart at eight hours nineteen 
okay 
thank you very much 
human operator. One of its most important conclu- 
sions was that callers appreciate the human operator 
over all kinds of automated systems. 
4 Information presentation in 
human-human OVR dialogues 
A study of a sample of 100 information dialogues 
out of a corpus of over 5000 dialogues shows that 
the presentation of a travel plan in a human-human 
dialogue involves more than just a monologue that 
presents the entire plan at once. The information 
presentation has a more interactive form. A human 
information service presents the travel plan in a step- 
wise way, generally giving at least one piece of new 
information with each turn. This presentation fol- 
lows the temporal order of the different stages in the 
travel plan. After each step in the information pre- 
sentation, the caller shows that he has processed the 
step by an acknowledgement. The dialogue fragment 
displayed in figure 2 shows an example of an infor- 
mation presentation in an OVR dialogue. We see 
that each step in the plan is acknowledged, before 
the next one is given. 
This stepwise presentation and acceptance of the 
travel plan is one of the most important character- 
istics of the information phase of a naturally occur- 
ring OVR dialogue. In this way, the operator is able 
to communicate the information as clear as possi- 
ble and the caller can relate the new information to 
information already known. 
Table 1 shows the quantitative facts that underly 
our description. It shows the amount of utterances 
the information service applies in one turn. We see 
that 87% of the turns contain only one utterance 
and 10% contain two utterances. The maximum of 
utterances per turn is 5, which is in only 0.4% of 
108 
the cases. Only in this case with five utterances, a 
whole travel plan is given at once. This confirms 
our view that in human-human OVR dialogues, the 
travel plan is given in steps. 
Table 1: The amount of utterances in each turn of 
the information service 
Amount of utterances percentage 
1 87% 
2 10% 
>3 3% 
A closer look at the exact information transfer in 
an OVR dialogue reveals even more about the exact 
information structure of the individual utterances of 
the information service. The information transfer in 
an OVR dialogue consists of three phases: 
1. a query phase, 
2. a search phase, and 
3. an information phase. 
During the query phase the caller poses his query, 
and the information service tries to understand this 
query as clear as possible. In the search phase (often 
indicated by a silence since the operator is search- 
ing), the information service applies the database 
query, and chooses the right travel plan. In the in- 
formation phase, the information service communi- 
cates the travel plan to the caller and the caller tries 
to get the plan as straight as possible. 
In each of these phases, different information ele- 
ments play a crucial role. During the query phase, 
these elements are the departure place, the arrival 
place, a global indication of the departure or ar- 
rival time, the day of travel, and if the caller wants 
a direct connection. The information service needs 
these information elements to compose an appropri- 
ate database query and to choose the most suitable 
travel plan. For the presentation of the travel plan, 
other information elements become important: the 
departure time, the arrival time, the places where to 
change, the directions of trains, the departure and 
arrival times at the places of change. The caller 
needs to know these information elements to carry 
out this plan. 
In the information phase, the information service 
uses these information elements to compose her pre- 
sentation. In general, she will use the elements that 
are already known from the query phase or from pre- 
vious utterances within the information phase, as a 
point of attachment for presenting the unknown el- 
ements. The order of the steps in the travel plan 
are the guiding principle behind the order in which 
the elements are presented. The dialogue fragment 
in figure 2 illustrates this. In the query phase of 
this dialogue, the speakers have established the day, 
a global arrival time, the arrival place, and the de- 
parture place. The information service has found 
a proper travel plan and starts her presentation. 
In consecutive turns, she gives the departure time 
(new) at the departure place (given), then the place 
where to change (new), then the departure time 
(new) at the place of change (given in the previ- 
ous utterance), then the arrival time (new) at the 
arrival place (given). 
Tables 2, 3, and 4 show the quantitative facts that 
underly our description. Table 2 shows the amount 
of information elements for each utterance of the in- 
formation service. We see that 69% of the utterances 
contain 2 information elements, that 18% contains 
only one element, and 12% contains 3 elements. This 
confirms our view that mainly two information ele- 
ments per utterance are given. 
Table 2: The amount of information elements in each 
utterance of the information service 
Information 
elements 
Percentage 
of utterances 
18% 
69% 
12% 
1% 
Table 3 shows the given-new divisions in utterances 
109 
with one, two, three, and four information elements 
respectively. We see that utterances with one ele- 
ment contain in most of the cases (68%) a new ele- 
ment. In the other cases (32%), they either refer to 
a crucial step in the information exchange, or give a 
alternative description of a previously introduced el- 
ement. We see that most utterances with more than 
one information element contain at least one new 
element. The given-new distinctions in the table re- 
flect the order in which the elements occur. One can 
observe that in utterances with two elements, the 
speakers prefer to mention the new element first, 
• while in case of three elements, speakers prefer to 
mention a given element first. 
Table 3: The given-new division in utterances with 
one, two, three, and four information elements 
respectively. 
Information 
elements 
Given-new division 
new 
given 
given-new 
given-given 
new-given 
new-new 
new-given-given 
new-new-given 
given-new-given 
given-new-new 
new-given-new 
new-new-new-new 
Percentage 
68% 
32% 
28% 
4% 
46% 
22% 
12% 
4% 
15% 
54% 
15% 
100% 
The table confirms our view that speakers tend to 
present at least one piece of new information per ut- 
terance. Usually, they will relate this new informa- 
tion with an entity introduced in the preceding con- 
text. This communicative rule was found in other 
corpora of spoken discourse as well (Chafe, 1987; 
Rats, 1996). 
Table 4 shows which specific information elements 
generally serve as given and which serve as new in- 
formation. We see that most departure and arrival 
times (97% in both cases) are new for the caller, 
while all departure and arrival places (100% in both 
cases) are known from the previous context. For 
the places of change and the directions, the result is 
roughly fifty-fifty. 
The table confirms our observation that departure 
and arrival places are generally introduced during 
the query phase and serve as given information dur- 
ing the information phase. On the contrary, places of 
change and the directions of train are mostly intro- 
duced in the information phase, and become given 
information after introduction. The departure and 
Table 4: 
elements 
Information element 
Departure time 
Arrival time 
Departure place 
Arrival place 
Place of change 
Direction 
The information status of the information 
in the information phase. 
Given 
3% 
3% 
100% 
100% 
54% 
42% 
New 
97% 
97% 
46% 
58% 
arrival times commonly serve as new information. 
After the presentation and acceptance of a whole 
travel plan, a caller may ask for new travel plans. 
This happens in 26% of the dialogues. Most of these 
plans (84%) concern earlier or later connections. In 
16% of the cases, the callers ask for another travel 
plan, for instance, for a connection from the station 
where the previous trip ended or another connection 
from the same departure place. 
5 Repair in the presentation phase 
Figure 2 shows an information phase where the caller 
has no problems in processing the presentation of 
the travel plan. Nevertheless, during communica- 
tion problems may arise. In such cases, the caller 
will interrupt the presentation by starting a repair 
sequence to solve the problem: 
• The caller will start a reconfirmation sequence, 
if he is not sure that he has heard the opera- 
tor's utterances well and he wants the informa- 
tion service to repeat, to complete, or to.confirm 
previously given information. A reconfirmation 
sequence consists of a reconfirm by the caller 
and an appropriate answer by the information 
service. 
• The caller will apply a clarification sequence, if 
he wants extra information about the current 
plan. A clarification sequence consists of a wh- 
question of the caller and an appropriate answer 
by the information service. 
• The caller will apply a checking sequence, if he 
wants to check extra information about the cur- 
rent plan that he suspects to be true. A check- 
ing sequence consists of a check by the caller 
and an appropriate answer by the information 
service. 
• The caller will start a correcting sequence, if he 
notices that the information service gives inap- 
propriate information. A correcting sequence 
consists of a correction and possibly a negative 
110 
acknowledgement by the caller and an appro- 
priate answer by the information service. 
In case the caller does not notice problems himself, 
the information service may infer from the caller's 
responses that the caller did not process her utter- 
ances as intended. She can infer this from his ac- 
knowledgements, but also from his reconfirmations, 
checks, and wh-questions. In such cases, she will in- 
terrupt the information presentation by a correcting 
sequence. 
Table 5 shows the frequency of the caller's repair 
sequences compalred with the presence of positive 
acknowledgements. We see that repair sequences 
do not occur as frequently as positive acknowledge- 
ments. Most of the caller's reactions (63%) are 
positive acknowledgements. Considerably less of 
the caller's reactions are wh-questions (4%), checks 
(10%), or reconfirmations (17%), and very few re- 
actions are corrections. In 6% of the cases, the re- 
actions concern questions for other or related travel 
plans. 
Table 5: Dialogue acts expressed by the caller in the 
information phase of an OVR dialogue 
Dialogue acts Frequency 
Positive acknowledgements 63% 
wh-questions 4% 
Checks 10% 
Reconfirmations 17% 
Corrections 0.3% 
Other (travel plans) 6% 
Repair sequences appear at different places in the 
information exchange. They may appear directly 
after the utterance to which they react. However, 
they may also occur after the acknowledgement of 
the utterance to which they react, and at the end 
of the complete presentation and acceptance of the 
travel plan. Table 6 shows the frequencies of these 
three possibilities for each repair act. 
We see that wh-questions, checks, and questions 
for an extra travel plan mainly occur after the com- 
plete presentation of the travel plan. By contrast, re- 
confirmations and corrections mainly occur directly 
after the problematic utterance. This difference is 
of course understandable. Reconfirmations and cor- 
rections directly concern problems in processing the 
previous utterance, while wh-questions and checks 
mainly ask or check extra information about the 
travel plan. It is more polite to keep these last kind 
of questions until the information service is ready 
with her presentation. 
Table 6: The place of the repair sequences in the 
Dialogue act 
wh-question 
Check 
Reconfirmation 
Correction 
Other(travel plan) 
after the 
problematic 
utterance 
10% 
90% 
100% 
after acknowl- 
edgement of 
the problem- 
atic utterance 
18% 
3% 
presentation 
after the 
complete 
presentation 
82% 
86% 
10% 
100% 
Nevertheless, the table shows that speakers may 
violate these habits, since they may utter re- 
confirmations after the whole presentation (10%) 
--although it seemed that they had understood and 
accepted it-- and wh-questions and checks directly 
after an informing utterance or the acknowledge- 
ment of that utterance. 
6 Towards a new strategy of 
information presentation 
Analysis of information presentation in VIOS and 
OVR dialogues shows an important difference in 
strategy. The VIos system presents complete travel 
plans as a whole, while human operators give the in- 
formation in several chunks. Future releases of VIOS 
will have to follow this latter strategy as much as 
possible, because it highly influences the apprecia- 
tion of clients. 
As a result, the travel plan will have to be divided 
in manageable chunks of information which follow 
the temporal order of the travel schedule. Each piece 
of information corresponds to a turn in the dialogue. 
Such a turn will introduce exactly one new informa- 
tion element as happens in most of the OVR dia- 
logues. This new information element will often be 
accompanied by an already given element. 
We have taken a first step in this direction, by 
extracting presentation scenarios for different di- 
alogues situations from our sample corpus. The 
choice for a certain scenario will depend on two types 
of information: 
1. the information elements that the system has 
gathered during the query phase, and 
2. the information that the system has received 
from the database query. 
The information acquired from the database will in- 
fluence the choice for a certain scenario most, since a 
travel scheme with two changes will result in another 
presentation than a direct connection. Nevertheless, 
the scenario must also contain the right given-new 
111 
combinations for the individual utterances. The in- 
formation elements that the system has gathered 
during the query phase will have to serve as the given 
information, while the new information that the sys- 
tem has received from the database query will have 
to function as the new information. 
Table 7 gives an example of such a scenario. It 
shows which scenario should be used, given cer- 
tain information elements gathered during the query 
phase and the information elements brought up by 
the database query. Each line in this scenario refers 
to a separate chunk of information. It also shows 
the order in which the elements should be uttered. 
The table also gives a possible linguistic form of the 
separate lines in the scenario. After each line, an ac- 
knowledgement or a short repair sequence may fol- 
low. 
The dialogue manager will incorporate the lines 
into separate statements and will send them one by 
one the text generator, awaiting the user's reaction 
before to decide to go on. The dialogue manager 
will proceed with the next chunk if the user has ac- 
knowledged the presented information. In this case, 
a relatively long period of silence can also be taken as 
a positive acknowledgement. If the user reacts by a 
wh-question, a check, or a reconfirmation, the appro- 
priate response will be given before it will continue 
the presentation. If a misinterpretation is detected 
the system will first start a correction sequence. 
When the complete presentation is finished and 
thus acknowledged by the caller, he may either finish 
the conversation or pose a new query. In the last 
case, the whole dialogue management process will be 
started again: the representation of the query will be 
updated, a new database query will be posed, and an 
appropriate scenario will be chosen. The same will 
happen when the user corrects the system because 
it does not give the plan he wants. 
To improve information presentation further, di- 
alogue management and text generation will have 
to collaborate intensively. The text generator will 
have to choose the right linguistic form, following 
Table 7: An example of a scenario 
Information given by 
the query phase: 
Information given by 
the database query: 
Scenario: 
Possible linguistic 
form: 
Departure place, arrival place, and a global indication of the departure 
or arrival time 
One train connection with one change, exact departure times, exact 
arrival times, place of change which is the same as the direction of the 
train, the direction of the second train is the same as the arrival place 
Departure_Time(new)-Departure_Place(given), 
Arrival_Time(new)-Place_of_Change(new), 
Place_oLChange(given)-Departure_Time(new)-Arrival_Place(given), 
Arrival_Place (given)-Arrival_Time (new). 
Ik heb een trein om \[DeT\] uit \[DeP\]. 
Die komt om \[ART\] aan in \[Poe\]. 
Daar vertrekt om \[DeT\] de trein naar \[ArP\] 
en dan bent u daar om \[ART\] 
( I have a train at \[DeT\] from \[DeP\]. 
It will arrive at \[ART\] in \[PoC\]. 
There will leave at \[DeT\] the train to \[ArP\] 
and then you will be there at \[ART\].) 
the prescribed dialogue act and given-new division. 
The corpus work described in Rats and Bunt (Rats 
and Bunt, 1997) on information packaging in Dutch 
information dialogues may be used for this. The di- 
alogue manager will probably have to incorporate 
extra contextual information into its instructions, in 
case several repair sequences will appear between 
two information chunks. Since in such a case, the 
system may have to use extra linguistic devices to 
show the user that he is going to continue the pre- 
sentation of the travel plan. 
7 Future Work 
We axe currently working on a precursor for the 
next version of VIos in which our ideas on au- 
tomated speech processing are incorporated (Vaxk 
et al., 1997). Dialogue management will have a pre- 
dominant role in this precursor as our study has 
shown dialogue management to be the significant 
difference between current ASP systems and human- 
human dialogues. The strategies described in the 
previous section will serve as an important system 
guideline to present information. We hope the next 
version will increase user's acceptancy of automated 
speech processing systems. 

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