1. Cognitive Model of Trust as Relational Capital
AAMAS 2007
Workshop on Trust in Agent Societies
May 14-18, Honolulu, Hawai'i
Castelfranchi C., Falcone R., Marzo F.
Institute of Cognitive Science and Technologies-CNR

2. outline Motivation Trust and relational capital
Cognitive model of being trusted
Dynamics of relational capital
Conclusion
05/15/2007
AAMAS Trust in Agent Societies

3. outline Motivation Trust and relational capital
Cognitive model of being trusted
Dynamics of relational capital
Conclusion
05/15/2007
AAMAS Trust in Agent Societies

4. motivation
what does it means that trust represents a strategic resource for agents that are trusted?
a model of ‘trust as a capital’
for individuals
implication for strategic action that can be performed
05/15/2007
AAMAS Trust in Agent Societies

5. motivation to be trusted:
increases the chance to be requested or accepted as a partner for exchange or cooperation;
improves the ‘price’, the contract that the agent can obtain.
05/15/2007
AAMAS Trust in Agent Societies

6. outline Motivation Trust and relational capital
Cognitive model of being trusted
Dynamics of relational capital
Conclusion
05/15/2007
AAMAS Trust in Agent Societies

7. Trust and relational capital
Relational capital vs Social capital
collective perspective, considering the advantages for the community
individualistic perspective, considering the advantages of the trusted agent
05/15/2007
AAMAS Trust in Agent Societies

8. Trust and relational capital
Relational capital vs Social capital
collective perspective, considering the advantages for the community
individualistic perspective, considering the advantages of the trusted agent
what is the competitive advantage not simply of being part of a network, but more precisely of being trusted in that network?
05/15/2007
AAMAS Trust in Agent Societies

9. Trust and relational capital
to be trusted usually is an advantage for the trustee: received trust is a capital that can be invested, and that requires decisions and costs to be cumulated;
trust has different sources: personal experience; circulating reputation; belongingness to certain groups or categories; the signs and the impressions that the trustee is able to produce;
05/15/2007
AAMAS Trust in Agent Societies

10. Trust and relational capital
the value of this capital is context dependent (for example, market dependent) and dynamic;
received trust strongly affects the ‘negotiation power’ that cannot simply be derived from the “dependence bilateral relationships”;
it is possible to measure this capital, which is relational and then depends on a position in a network of relationships.
05/15/2007
AAMAS Trust in Agent Societies

11. outline Motivation Trust and relational capital
Cognitive model of being trusted
Dynamics of relational capital
Conclusion
05/15/2007
AAMAS Trust in Agent Societies

12. Cognitive model of being trusted
Objective and Subjective Dependence
let Agt={Ag1,..,Agn} a set of agents;
we can associate to each agent Agi  Agt:
a set of goals Gi={gi1,..,giq};
a set of actions Azi={i1,..,iz}; these are the elementary actions that Agi is able to perform;
a set of plans ∏ = ={pi1,..,pis}; the Agi’s plan library:
the set of rules/prescriptions for aggregating the actions;
a set of resources Ri={ri1,..,rim}.
05/15/2007
AAMAS Trust in Agent Societies

13. Cognitive model of being trusted
An agent Agj has an Objective Dependence Relationship with agent Agi with
respect to a goal gjk if for achieving gjk are necessary actions, plans and/or resources
that are owned by Agi and not owned by Agj
05/15/2007
AAMAS Trust in Agent Societies

14. Cognitive model of being trusted
A is the set of agents who depend from Agj for something (actions, plans, resources)
B is the set of agents from which Agj depends for achieving an own specific goal gjk.
C is the set of agents with whom Agj could potentially negotiate for achieving support for gjk A C B
The greater the overlap the greater the negotiation power of Agj in that context.
05/15/2007
AAMAS Trust in Agent Societies

15. Cognitive model of being trusted
The dependence relationships should be re-modulated on the basis of the agent subjective interpretation (sets as believed by each agent)
Subj-Dependence(Agj, Agi, gjk) represents the Agj’s point of view with respect to its dependence relationships
05/15/2007
AAMAS Trust in Agent Societies

16. Cognitive model of being trusted
Objective Potential for negotiation of Agj  Agt about a goal of own gjk
OPN(Agj, gjk)
Subjective Potential for Negotiation of Agj  Agt about an its own goal gjk
SPN(Agj, gjk)
05/15/2007
AAMAS Trust in Agent Societies

17. Cognitive model of being trusted
but there will be not exchange in the market if there is not trust to enforce these connections.
A represents the set of agents who depend from Agj for something (actions, plans, resources)
B represents the set of agents from which Agj depends for achieving an own specific goal gjk.
D includes the set of agents that Agj considers trustworthy for achieving gjk D A C B
05/15/2007
AAMAS Trust in Agent Societies

18. Cognitive model of being trusted
E includes agents who depend form Agj, who are trusted but on different tasks;
F includes agents not depending from Agj and trusted on different tasks;
G includes agents trusted for the achievement of the goal gjk but not depending from Agj. A E G F B
05/15/2007
AAMAS Trust in Agent Societies

19. Cognitive model of being trusted
Subjective Trust Capital of Agi  Agt about a specific task τk, the function:
STC(Agi, τk) =  Do (Belji(Ajk))*Do(Belji(Wjk))
Where n is the number of agents need the task τk. Agj, Agi  Agt.
Do(Belji (Aik)) means the Aj’s degree of belief (believed by Ai) with respect the Ai’s ability about the task τk.
Do(Belji (Wik)) means the Aj’s degree of belief (believed by Ai) with respect the Ai’s willingness about the task τk n
j=1
05/15/2007
AAMAS Trust in Agent Societies

20. Cognitive model of being trusted
Subjective Usable Trust Capital of Agi  Agt about a task of its owns τk:
SUTC(Agi, τk) =
=  (Do (Belji(Ajk))*Do(Belji(Wjk)))/(1+pkj)
Where pkj is the number of other agents in the dependence network that can achieve the same task with a trust value comparable with the one of Agi. n
j=1
05/15/2007
AAMAS Trust in Agent Societies

21. outline Motivation Trust and relational capital
Cognitive model of being trusted
Dynamics of relational capital
Conclusion
05/15/2007
AAMAS Trust in Agent Societies

22. Dynamics of relational capital
relational capital is peculiar in its being crucially based on beliefs: what makes relationships become a capital is not simply the structure of the networks (who “sees” whom and how clearly) but the levels of trust which characterizes the links in the networks
relational capital is a form of capital, which can be manipulated by manipulating beliefs
05/15/2007
AAMAS Trust in Agent Societies

23. Dynamics of relational capital
There is a cost of this Capital.
One has to invest to acquire it
Example: in iterated strategic games, the cost of building my Reputation is an investment for future interaction
05/15/2007
AAMAS Trust in Agent Societies

24. Dynamics of relational capital
strategies that can be performed to enforce the other’s dependence beliefs and in particular his beliefs about agent’s competence:
i) Agi can make the other agent dependent on him by making the other lacking some resource or skill (or at least inducing the other to believe so)
ii) Agi can make the other agent dependent on him by activating or inducing in it a given goal (need, desire) on which the other is not autonomous (or it believes so).
iv) Agi can work for reducing the b
elieved (by Agj) value of ability of each of the possible competitors
iii) Agi can activate, in her plan of actions, sub-goals to signal her presence and her skills
05/15/2007
AAMAS Trust in Agent Societies

25. Dynamics of relational capital
being trusted by a particular agent can mean thRelational capital can also circulate inside a given society
it is strategically important for the agent to know very well how this happens and in which ways (not only figurate) trust begin to expand and keep on doing it
at an agent has one more agent in her relational capital
trust of another agent can be very useful and exponentially increase agent’s capital thanks to the strategic role or position of this other agent
05/15/2007
AAMAS Trust in Agent Societies

26. Dynamics of relational capital
being able is not necessarily the cause of trust (it can be the case of a diffuse atmosphere that makes the others to trust the agent although the agent has not all the characteristics to be trusted)
difference between how the others actually trust an agent and what that agent believes about that
difference between the believed trust of others on an agent and the level of trustworthiness that agent perceives in herself
05/15/2007
AAMAS Trust in Agent Societies

27. Conclusion
Trust is not only a ‘social capital’ a collective advantage, but also a competitive Relational capital
The value of agents in a given market is not only due to interdependency but also to cumulated trust (comparative evaluations)
How is this capital acquired and transferred?
05/15/2007
AAMAS Trust in Agent Societies