ABSTRACT 
Language interaction (LI) as a part of inter- 
personal communication is considerably influenced by 
psychological and social roles nf the partners and 
their pragmatic goals. These aspects of communica- 
tion should be accounted for while elaborating 
advanced user-computer dialogue systems and develop- 
ing formal models of LI. We propose here a formal 
description of communicative context of Li-situa- 
tion, namely, a system of indices of LI agents' 
interest in achieving various pragmatic purposes and 
a system of contracts which reflect social and 
psychological roles of the LI agents and conventio- 
nalize their "rights" and "duties" in tlle LI- 
process. Different values of these parameters of 
communication allow us to state possibility or/and 
necessity of certain types of speech acts under 
certain conditious of LI-situation. 
1. INTRODUCTION 
ELEMENTARY CONTRACTS 
AS A PRAGMATIC BASIS OF LANGUAGE INTERACTION 
E.L. Pershina 
A\[ Laboratory, Computer Center 
Siberian Division of the USSR Ae. Sei. 
Novosibirsk 630090, USSR 
goals. The value t of this threshold is indivldual 
for each agent in different communicative situation. 
The values of these indices are generated under 
the influence of different psychological, ethical, 
pragmatical and other factors. The degree of 
importance of each factor is determined by 
individual characteristics of each agent and may 
vary during the LI-process. Hence the values of 
relevancy indices may also vary. 
We consider interpersonal communication as 
joint activity of LI agents (X and Y). Each agent 
has his own plan of behaviour which is represented 
here by a system of goals (G.X or G.V), i.e.certain 
pragmatic and communicative tasks to be realized. 
The system of goals of the agent, for instance,G.X, 
may contain both the goals initiated by X himself 
and the goals initiated by his partner Y. Formation 
of the system of goals by the agent X is associated 
with the twu following communicative metagoais: 
-kl is an inclusion of a goal g into the 
partner's system of goals G.Y; 
--k2 is an inclusion of a goal g into X's own 
system of goals G.X. 
Language interaction is considered as a process 
aimed at accomplishing one of these metagoals. Each 
agent chooses a mode of achieving metagoals iu 
response to socially determined relations between 
him and his partner. These relations are described 
by a system of contracts (\[1\],\[2\],\[3\]). In this 
paper we propose a formal description of some 
elementary contracts formed by combination of basic 
relations between the partners. 
2. THE SYSTEM OF RELEVANCY INDICES. 
In order to describe agents' positions with 
respect to a potential goal g we introduce three 
indices being individual for each agent: 
-INT(X,g) is a degree of X's interest 
(necessity, desirability) in achieving tile goal g; 
this index may be either positive or negative; 
-CST(X,g) is a cost of achieving tile goal g, 
i.e. the efforts to be made by X for achieving g; 
this index is always positive; 
-BEN(X,g) is a benefit which may be derived by 
X from achieving g; BEN(X,g)=INT(X,g)-CST(X,g). 
We consider some threshold t which,in general 
case, shouhl be exceeded by BEN(X,g) (BEN(X,g}>t) 
for including the goal g into the X's system of 
3. DOMINATION AND DEPENDENCY 
3.1. In order to map contracts onto 
communicative level of the LI we introduce several 
types of elementary contracts formed by combination 
of basic domination cud dependency relations between 
the partners. These relations control over the 
process of forming the system of goals, i.e. they 
influence upon the choice of the mode of achieving 
the metagoals. The domination relation fixes LI 
agent's "rights" and "duties" in achieving metagoal 
kl, i.e. in including a goal into the partner's 
system of goals. Dependency controls over achieving 
the metagoal k2. The "rights" and "duties" of the 
agent in the process of goal formation are 
represented by a set of rules known to both the 
agents. These rules belong to a set M which 
represents the agents' mutually coordinated beliefs 
about the world. 
3.2. Elementary contracts of the first type are 
based on the domination of X over Y for all the 
goals of the class G'. This relation allows X to 
oblige Y to include any goal g~G' into Y's system 
of goals, if the proposition BEN(Y,g)>tl belongs to 
tbe set M, tl being the minimum value of index 
BEN(Y,g) which is necessary for X to achieve the 
metagoal kl=(gEG.Y.). 1'he value of tl is determined 
by the whole complex of constituents of complete 
contract which determines the level of cooperation, 
i.e.the degree of coordination of agents' actions, 
coincidence or conflict of their interests. So, 
provided that (X>Y,G',tl), g~G' and BEN(Y,g)>tl, it 
is sufficient for X to let Y know of metagoal kl= 
(g~G.Y) being included in the system G.X for the 
goal g to be included into the Y's system of goals. 
The second type of elementary contracts is 
characterized by tile absence of domination of X over 
Y (X~Y,G',t2): in general case it is not sufficient 
for X to let Y know of metagoal kI=(gEG.Y) being 
included in G.X. For X another way of achieving kl 
based on the values of some other constituents of 
the contract should be chosen. 
3.3. Elementary contracts wbich regulate 
achievement of tile metagoal k2 are based on the 
dependency relation: (X<Y,G',t3) . If X depends on 
Y, it is necessary for him to get Y's permission for 
inclusion of a goal g~S' into the X's system of 
goals, or the proposition BEN(Y,g~G.X)>t3 should 
belong to the set M, where t3 is the necessary 
value of index BEN for V to include a goal into his 
system of goals. 
229 
The absence of dependency (X~Y,G',t4) allows X 
to include any goal g66' into his system of goals 
without Y's permission. But the index BEN(Y,g~G.X) 
has to exceed the value t4 being determined by the 
level of cooperation between the partners. 
3.4. The basic *'elations aren't mutually 
exclusive or interdependent: the domination of X 
over Y in the class G' doesn't exclude the domina- 
tion of Y over X in the same class G' and doesn't 
presuppose the Y's dependency on X. The complete 
contract includes decomposition of the set of poten- 
tial goals into classes, for each of which the given 
relations are defined on the part of X as well as on 
the part of Y, 
4. NEUTRALITY, COOPERATION AND CONFLICT 
4.l.Basie relations reflect certain social and 
psychological roles of the LI agents. The absence of 
these relations between the partners leaves the 
modes of achieving the metagoals to LI agents' 
choice. These modes are divided into three groups, 
according to the degree of mutually accounting for 
each other's intercs£s. These groups determine three 
types of contracts: neutral, cooperative and 
conflicting ones. There exists the follwing set of 
modes: admissibility/inadmissibility of deformation 
of the basic relations, possibility of reciprocal 
concessions, usage of additional information 
stimulating a successful achievement of the agent's 
goal. This stimulus may be positive (plus-stimulus) 
or negative (minus-stimulus). 
4,2. The neutral contract presupposes the 
inadmissibility of deformation of tile basic 
relations. 
In case of absence of domination of X over Y 
(X~Y,G',t2) it is necessary for X to make Y be 
interested in achievement of a goal gE G' for 
realizing the metagoal kI=(E6G.Y), i.e. to make the 
value of index BEN(Y,g) > t2. Neutral contracts 
allows X to use one of two possible means: a) to let 
Y know of some information increasing the value of 
the index BEN(Y,g); and b) to let Y know of a goal 
g' being included in the X's system of goals, with 
BEN(Y,g')+BEN(Y,g)>t2. Provided that the proposition 
BEN(Y,g)<t2 belongs to the set M and it is 
impossible fur X to use one of the two means 
mentioned above, X has to give up the meta- 
goal kl=(g~G.Y). 
In case of (X~Y,G',t4) the neutral contract 
commits X to take Y's interests into account. X may 
include a goal g into G.X if this goal is harmless 
for Y (INT (Y,g)>O). If the value of the index 
INT(Y,g) is negative, it is necessary for X to 
guarantee some compensation for presupposed damage, 
i.e. to include a goal g' into G.X. with BEN(Y, 
g~ G.X)+BEN(Y,g' 6 O.X)>t4. Otherwise X has to give 
his goal g up. 
So neutral contracts provide the accomplishment 
of the metagoals by means of basic relations and by 
using plus-stimuli. 
4.3. Cooperative contracts are characterized by 
reciprocal "credit", i.e. mutual concessions are 
possible. Each agent may allow infringement of his 
interests. The degree of infringement is determined 
by the level of cooperation and is fixed in the 
values ti of relevancy indices. Cooperative 
contracts allow modification of basic relations, it 
is possible for any agent not to do his duty or to 
230 
exceed, his rights. 
In case of X>Y the inclusion of a goal into the 
system G.Y is possible if the value of the index 
CST(V,g) is far less than t5 and the value of tile 
index BEN(X,g) is more than t6, where t5 and t6 are 
determined by the level of cooperation. If the value 
of index CST(Y,g) is more than t5 but X doesn't give 
up the metagoal kl=(g~G.Y}, then X may use plus- 
stimulus, i.e. compensation of presupposed damage. 
In case of X~Y it is possible for X to achieve 
the metagoal kI=(gEG.Y) without using any stimulus, 
if the value of the index CST(Y,g) is less than t5 
Provided that CST(Y,g)>t5, X has to use plus- 
stimulus for including the goal g into the G.Y 
system. The partner Y, on his turn, has to include 
the goal g into his system of goals, if CST(Y,g)<t5 
and BEN(X,g)>t6. 
Cooperation permits the modification of the 
basic relation X<Y, it means that it is possible for 
X to include a goal g into his system of 
goals in spite of the value of the index 
BEN(V,gQG.X) being less than t2. In other words, Y 
may give permission for X's inclusion of the goal g 
into the system G.X in spite of BEN(Y,gE G.X)<t2 
If the value of the index BEN(Y,g~G.X) is far less 
than t2 then it is necessary for X to use plus- 
stimulus: to promise the inclusion of the 
goal g', with BEN(Y,gEG.X)+BEN(Y,g~ G.Y)>t2. 
In case of X<¥ it is necessary for X to take 
into account Y'x interests: to include a goal with 
INT(Y,g6G.X)>O. Provided that INT(Y,g~G.X)<O, it 
is necessary for X to guarantee compensation for 
success of the metagoal k2=(g~G.X). As for ¥, it is 
possible for him to a/low some infringement of his 
interests: X may include a goal g into G.X, if the 
value of index BEN(Y,gEG.X) is not much less than 
t2. In this case X may succeed in achievement of tile 
metagoal k2=(g~G.X) without using of plus-stimulus. 
4.4. The conflicting contracts allow agents to 
use minus-stimulus and to break tile basic rela- 
tions. 
The break of elementary contracts based on X's 
domination over V is characterized by Y's refusal of 
including the goal g into his system of goals in 
spite of X's demand, if the value of the iadex 
BEN(Y,g) is less than tl. 
As for, X it is possible for him to use a 
minus--stimulus for achieving the metagoal k\]= 
(g~ G,Y) in both the cases X>V and X}Y. Minus- 
stimulus is X's promise to include a goal g' into 
G.X with BEN(Y,g'E G.X) being far less than t2. This 
promise induces Y to inclade the goal g into G.Y in 
order to avoid accomplishment of the goal g'. Under 
a conflict for achieving the metagoal k2= 
(gE G.X) it is possible for X not to get Y's 
permission for including a goal g into G.X in both 
tile cases X<Y and X~V. Conflicting contracts allow X 
to include any goal without taking into account Y's 
interests. If it is necessary for X to get Y's 
permission for achieving the goal g, he may use 
minus-stimulus to force assent out of Y. 
5. CONCLUSION 
Above we have discussed certain aspects of 
communicative context of LI: the agents' systems of 
indices of relevancy, basic relations forming 
elementary contracts and three types of contracts 
regulating the process of goal formation. These 
aspects of goal formation reflect some social and 
psychologica\] roles of the LI agents, 
It is convenient for us to consider LI to be 
aimed at forming agents' systems of goals in order 
to map "rights" and "duties" of agents onto 
communicative level and to state possibility or/and 
necessity of a certain type of speech acts in tile 
process of goal formation. 
Fop accomplishment of tire metagoal kl (inclu-- 
sion of a goal into Y's system of goals) it is 
necessary for X to perform a speech act which may be 
named "inducing". The particular type of inducing 
speech act is determined by the relation which holds 
between X and Y. X's domination over Y allows X to 
perform a speech act which may Ire named "order", 
otherwise X performs a speech act "request". It" it 
is necessary fat' X to use additional information, 
the type of speech act performed by X is determined 
by tile type of information to be chosen in 
accordance with tile type st' contract : 
neutral and cooperative contracts allow X to use 
only plus-stimulus, that is X performs a speech act 
of the type "temptatimV'. Conflicting contract 
allows X to perform a speech act "threat" which is 
characterized l)y ase of minus--stillluius. 
X's dependenry upen Y makes it necessary for X 
to perform a speech act of tile type "asking 
permission" fer in(:lusion of a g'oal into his system 
G.X. If this goal g is relevant for X, then "asl¢ing 
permission" i,ay be X's "asking permission" for doing 
something ill favour of X ("May I collie in ?"). If the 
goal is relevant for Y, then X performs all "offer" 
("What about a cup of tea?", "May I see you home?") 
'rile proposed systelll of nol:Jons is a first step 
towards formalization of tire aspects of communica. 
tire context discussed above. The task for future 
work is to extend tile nomenclatare of clenleatary 
contrac ks and to specify forlaaJ means for 
representation of social and psychological roles of 
the LI agents. 
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