MODELING DIALOGUE BY FUNCTIONAL 
SUBCATEGORIZATION 
J. R. Zubizarreta Aizpuru 
Facultad de Inform~itica 
U.P.V-E.H.U. San Sebastian, Spain 
E-mail : jipzuaij@si.ehu.es 
Abstract 
In this paper we present a dialogue model which has 
as its main goat to place in context the utterance 
generated by the speaker. The dialogue model 
considers that an intervention generates one or more 
ilocutive acts which are handled as flmctions. These 
functions subcategorize to or are subcategorized by 
other functions in the dialogue. 
The model uses an exchange schema with the 
purpose of expressing the different ftmctional 
subcategorizations. These schemas have properties 
close to the semantic forms of the verbs in a lexical- 
functional context. 
1 INTRODUCTION 
In task-orientetl dialogues two speakers work in 
cooperation with the purpose of carrying out a plan. 
This type of interaction has a start and a development 
structured by the restrictions of space, thne, transaction 
object and role of the partieipanls. 
A number of researchers \[Grosz and Sidner, 86; 
Litman and Allen, 87; Ramshaw, 91; I.ambert and 
Carberry, 9211 have suggested that a coherent discourse 
consists of segments that are related to one another 
through some type of structuring relation. Our dialogue 
model tries to capture the goal-oriented nature of 
discourse, ideutifing the discourse structure by providing 
the details of a computational mechanism for 
recognizing the structural relationships. 
The model enables the incremental recognition of 
communicative goals using rewriting rules and 
functional equations. The grammar constructs the 
structural tree captnring the dialogical functions of the 
discourse using functional snbcategorization. The 
subcategorization process improves on previous 
approaches \[Ferrary et al., 88; Bilage, 91; JOnsson, 911, 
increasing the expresive power of the traditional dialogue 
models by modeling the relationships among the 
communicative actions enabling the task of connecting 
discottr~. 
The different parts of the system have been 
implemented using a blackboard architecture. The 
process starts obUfining the f-slructure associated to the 
intervention making use of a lexical-functional grammar 
\[Abaitua ct al., 9111. In a second phase the f-structure is 
refined providing the correct explanation, essentially it 
solves the verbal interpretation and obtains referential 
Craig Jones 
Department of Computer Science 
University of Aberdeen, Scotland-U.K, 
information. Then, the planner and/or the dialogue 
module suu't to work. 
In the remainder of this paper, we will present our 
dialogue model in a top-down manner. Firstly, we show 
the exchange structure attoptexl and the subcategorization 
process using two samples. Then, we explain the 
retroactive and proactive nature of the interaction and we 
conclude by presenting two kinds of special 
interventions, the complex ~lll(l compound interventions. 
2 EXCIIANGE STRUCTURE 
We assign to the constituents of the exchange level 
initiative and reactive ilocutive functions. These 
functions qualify ctmstituents which are in the same 
level of structuration. The initiative functions are 
assigned to the directriee interventions of the exchange. 
The reactive functions constitute the generic class of the 
answers and they try to satisfy the obligations assumed 
for the interpretation of the initiative functions. 
Analyzing the corpus that we dispose we have 
detected the following initiative functions : Fre q, Fre q- 
prel l , Freq_aux, Freq_fic, Fqinlbr m, Fqref and Fqi f. Fre q 
is a function associated with a petition of achievement a 
physical action. Fqinlbr m inquires inlonnation about the 
plan in progress. Fqref and Fqi f demand referential and 
polar information. 
The above initiative functions are completed with the 
lollowing reactive functions : Finformre q, Finform, 
Fiafref and Finfif. 
We assign to the initiative functions, with directrice 
characteristics, one exchange schema with similar 
performance to the semantic forms of the verbs in a 
lexical-functienal context. This exchange schema will tx~ 
identified from now with the word SCItEMA. An 
schema specification will exhibit the subcategorizations 
detected inside an exchange. Therefore, an exchange with 
au initiative function of type Fqinfor m, inside which a 
nested exchange has been produced, will have the 
following schematic representation : 
SCHEMA = "Fqinform# < ( 1" Ecomp ) ( T Finform)>" 
l Freq_prel, Freq_au x and Freq_fi c are functions 
subcategorized by Fre q and represent preliminaries, auxiliar 
forms of the request mid fictitious executions of actions. 
8i3 
SCHEMA = "<( \[Sugcategorized_by\] ) > # F x # 
<( \[Sugcategorizeto\] )>" 
Just like in a lexical-functional grammar, the initiative 
function Fqinfor m subcategorizes to the reactive function 
Finform and to a subexchange identified by Ecomp. This 
subexchange has, at the same time, a specific initiative 
function which subeategorizes to the appropriate reactive 
function and which is subeategorized by the Fqinfor m 
function. One example of dialogue sequence where this 
schema could be applied is the following : 
$1.- How does it modify the camera's diafragm ? 
(Fqinform) 
$2.- Do you know where is the key for modifying it ? 
(Fqif) 
$1.- Yes, in the left part of the camera (Finfi f + 
Finfref) 
$2.- Ok, then press the F3 buttom and move the key 
towards the left (Finform) 
In the model which we are going to present both the 
exchange structure and the intervention structure are going 
to be definied using rewriting rules. The tree nodes will be 
enrichied with functional stmcifications just like a lexical- 
functional grammar. These functional specifications will 
reference to the initiative and reactive fimctions which are 
going to appear in the conversation. 
The grammar initialy will have the following rules : 
(1) D --> E 1 ............... E i .............. E n 
(1" EF1)---J, (T EFi)=~ (T EFn)=$ 
D represents a dialogue, E i the exchange i and EF i the 
functional specification of the exchange i. 
(2) E i -> I l 12 (I 3) 
(T Fx)= $ (T Fy)= $ 
Ij represents the intervention j of exchange E i. 
Both F x and Fy represent speech acts of the form F(p). 
That is to say, every node I i will not reflect only the 
referential and predicative aspect of the interation but also 
will express the ilocutive force associated to every speech 
act. A single exchange will be constituted for an initiative 
intervention and we could suggest nuclear to the exchange, 
an initiative-reactive intervention and optionaly for a 
closure reactive intervention of the exchange. 
The functions F x and Fy associated with every 
constituent will be instantiated for some of the initiative 
and reactive fimctions introduced before. 
The rule (2) formulated above handles balancod 
conversational sequences, that is to my, sequences of the 
following form : 
$1(11).- Please, change the exposure mode. 
$2(12).- I changed it already and 1 have left it in 
PROGRAM. 
$1(13_1).- Ok, let us continue, how can 1 change the 
speed ? 
$2(I2).- Press the key XY23 and move the lever. 
The structural-functional tree which would correspond 
to this dialogue piece would be the one showed in Fig. 1. 
Structuraly the dialogue fragment would be constituted by 
two exchanges which inform about the physical actions 
performed by the speaker and which are connected with a 
high level task. 
Let us imagine that instead of the previous dialogue 
piece we produce another one modified a little : 
$1(11).- Please, change the exposure mode. 
$2(1"1).- Sorry, how do I change it ? 
S1(I'2).- Yes, press the buttom MODE and move 
the lever on the right side. 
$2(12).- I changed it already and i have left it in 
PR 0 GRAM. 
$1(13).- Ok, let us continue ....... 
This second dialogue illustrates a very common 
phenomena, the speaker departs, momentarily, from the 
main direction of the conversation, in order to start a 
secondary exchange which, in most cases, will have a 
subgoal to be achieved, and then returns to the main axis 
of the convermtion. 
In order to manager these cases we propose a rule like 
this : 
(3) E i --> I 1 E" i 12 
t = ~, ( T Ecomp) = .L ( \]" Fy) = .~ 
Fig. 2 shows the dialogue structure obtained by means 
of the aplication of the above rule. We associate the 
schema 2.a to an exchange which has, like initiative 
intervention, a request function of achievement physical 
actions. At the .same time, this function subeategorizes to 
an subordinate exchange - Ecomp- and a reactive 
intervention. 
We emphasize that the subordinate exchange Ecomp 
has a retroactive nature so that it would not appear at the 
moment of the initial formulation of the schema. 
The schema 2.b is a bit different from the standard 
notation of a lexical-functional grammar, it specifies an 
element in the left hand side of the nuclear function. This 
element will be at the same time the nuclear function of 
another exchange and reflects the subeategorization that 
exists between this element and the nuclear constituent of 
the subordinate exchange. 
The subexchange E" i especified above like E" i --> I" I 
I'2, can have, of course, nested dialogues defined with the 
rule E'i--> I" 1 (E'" i) I" 2. Iu our corpus we do not find 
subdialogues with more than three nested levels very 
often. 
814 
7"=1 /"/l~ 
(t Finfo~,req)ir,~~ tl"! \ =t 
/ ( 1' Freq) = ~ (t SA)=t = .. ,~ 
q:req 11 <( T Fiuformre 
/ SCIIEMAtic = 
q:qif tf <(T Finfil)> 
E 
( I EF2)= .\[ 
jl>,. \ ( 1" |qtlfoltn) = 1 
( t Finformrcq CJON'I'IN 
: . , . = 
"Fqinform J/< ( I l~inlbnn) >~ 
Fig. l Structural-functional tree of a balanced conversational sequence 
I) 
1=,1, 
/ ( I Freq) = it, 
SCIIFMA (2.;0 = 
"Frcq # / (1 Fqinform) = 
<( T Finlbrmrcq)( 1 Econq)) SCIlEMA (2.13)= \[ 
"l;req # Fqint\mn # I 
<(I" Finform)>" ~ \[ 
(I ~liFl) = I 
(~ Ecomp)=l J.\ 
1 =1 (I Fillbrm)=l. (I 
0 
( 1 l:inftmnrcq) = l- 
Ar) = 1. I = I 
(1 liF2) = 1 
1!2 
( T Fqif) =~ 
I 
SCI IEIvlAlic = 
qklif#<(I l:infif)>" 
Fig. 2 Dialogue structure with subordinate exchanges 
81,5 
3 PROACTIVE AND REACTIVE 
FEATURES IN THE INTERVENTION 
An intervention will be composed by a main act that 
we will designate director act, preceded and/or followed by 
option,'d subordinate acts. The director act is the speech act 
that provides the general sense of the intervention, that is 
to say, its ilocutive force. 
In all intervention the interactive functions will be 
expressed using the proactive or retroactive features that we 
will associate to the intervention. 
The following rules define the structure of an 
inlervcntiou: 
I i --> (X*) I D (X*) 
(1" SA)c=+ t =$ (1` SA)c =+ 
X--> { Ipi , Iri } 
(1" SAp)=$ (T SAr)=$ 
The first rule defines file hierarchical relation that 
exists between the director act (I B) and its subordinate acts 
coustraiuted by functional equations. The second rule 
identifies the subordinate act like proactive or retroactive. 
3,1 Complex interventions and 
compound interventions 
In most cases, the reactive and proactive features of the 
subordinate acts are not related to the director act of the 
intervention where they appear. In these cases the 
subordinate act must find ils director act in the dialogue 
sequeuce, basiealy belore, but sometimes it must wait for 
the next interventions for its subcategorization. 
The presence of this phenomena creates the necessity to 
extend the original model with the inclusiou of 
mechanisms which enable to deal with another two new 
types of interventions: the complex interveutions and the 
compound interventions. 
The complex interventious are constituted of two or 
more subintcrvcntions with a relation of local domain, that 
is to say, the subinterventions make reference to the 
initialive fuuction of the exchange more immediate. 
These interventions will have the following 
formulatiou in the model 
E --> I l 
(1" F~)=$ 
Ix --> Ix 1 
( 1" l,'xl ) = $ 
1 X 
( 1" lcomp 1) = 
Ix2 
$ Fx2) = $ 
The schema assigned to the exchange inside of which it 
is the complex intervention will be the following : 
SCIIEMA = "F l # < {( 1" Fxl ) ( q" Fx2) } ( T Freac ) >" 
F l subcategorizes to 1,'reac using the initiative function 
(Fx2) of the complex intervention. 
The compound interventions are constituted of two or 
more subinterventions too, between them there is a 
relation of non local domain. In the cases of ploaclive 
movement the domain nature will remain defined a 
posteriori. 
The compouml interventions will have the following 
folTnulation : 
E --> I l Iy 
(1' FI)=$ (i" Icomp )=$ 
ly --> Iy l Iy 2 
(1" Fy 1)=$ ($ Fy2)=$ 
{(~ = g),(1` =~)} 
The schema assigned It this exchange will be the 
following : 
SCIIEMA = T l # < ( $ Fyt) > ( 1" 1,'y2)" 
The function l:y 2 is subcategorizcd by the function 1" l 
but does not support thematic relations wilh it. These 
functions will be rcactives and will have non local domain 
or proactives which produce a thematic rupture with the 
initiative function F 1. 
We illustrate all this with the lollowing dialogue 
fragment : 
S 1.- Now I do not see anything 
S 2.- Please, press the shooter half way. 
S 1.- Where is it ? 
$2.- Close to the screen, a red buttom do you 
see ? 
$1.- Yes, yes symbols appear but 1 do not 
understand them. 
Ilow we can set in Fig. 3 the stthordinate exchange 
Ecomp geuerates a complex intervention like a reaction to 
the nuclear initiative function of the exchange. This 
complex intervention is composed of two subintervcntions 
of reactive and initiative nalare . This hlct makes them 
both appear between curly-braces pointing out that we are 
treating the same intervention. The presence of the 
initiative fimction Fqi f generates the schema 3.3 where the 
initiative function is subcategorizcd by the former 
initiative lunction (l:qrcf) and subcategorizcs, at the s~une 
time, to the reactive function (Fiufif) that appear 
subcategorized in tile former schema. This function 
represents an expectation generated fl)r Fqi f in 3.2 and an 
achievement iu 3.3. 
The schema 3.3 is related to a compound iulervcution 
where one of the subinlcrvcnlions plays a reactive role 
associated with the former intervention. The next 
subintervcntion, reactive too, is non local aud therefore is 
not subcategorized fi~r tile nuclear finlction of the schema 
3.3. This subinterveutiou is subeategorized for the 
function Fre q of the schema 3.1. The metavariables g and 
show the relation of non local domain thai exists 
between bo|h functions. 
816 
( I \[:inform ) = 1 
~(3.1) 
II --> S l 
I = 1 
( t I:rec0 = 
t = ~I:infonnreq £ 
I2-->$2 
T = ~ (l Icompl)= 1 
/ ~ I4--> $2 I (3.2) ( T Fqref) = t 1,1 
(3.1) S('IlI,;MA = "lheq# <( I 1;in\[bnnreq) (r licomp) > ( ! l:in 
( 3.2 ) SC'III,;MA = "< ( ! li'eq) > tf l~qref # 
<l(r Finfrel)( I lqi0} ( I l{nfi0>" 
( 3,3 ) S('I1EMA = "< ( t l:qreO > # Fqif g < ( T 17infil) > ( t Finlbnurc~ 
( I l:qi0 = ,t ( 1" l:infit) = ,t ~: I "* ~ "iJl:hlr~rmre-~ \[0f ) 
Fig. 3 Complex and compound interventions 
\[B ilange, 91 \] Bilange, 1 ~.( 1991). "A Iask independent oral 4 CONCLUSIONS 
We have presented a dialogue model that uses 
functional subcalcgorizatiou for recognizing Ihc structural 
relalionships of the discourse. The subcategorization 
process applies a slruetural schema to every exchange 
producing a functional definition with properlies close to 
the semantic forms of tile verbs in a lexical-funetknlal 
grammar. 
The model enables us to handle subordinate exchangcs 
capluring tile dependencies Ihat exist among the ilocutive 
f/mctiotls relating tile main function of the exchange to 
tile initiative function of tile subordinate exchange. Tim 
complex and compound interventions make use of tim 
same mechanism of subcalegorizatiou using Ihe proactive 
and relroaclive features of Ihe interventious. 
The parser has been written ill Pmlog with a bottom- 
up slrategie. The interface between tile blacklx/ard and the 
differeul Knowledge BasKs has been implemented in 
Common l.isp. The control mechanism uses the 
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