Plan of the tutorial Introduction Normative systems The agent perspective: normative multiagent systems The construction of social reality website: .

Plan of the tutorial

• Introduction• Normative systems• The agent perspective: normative

multiagent systems• The construction of social reality

website: http://normas.di.unito.it/iat04

Introduction

Social norms

In the Multi Agent Systems field, social norms are perceived to help improve coordination and cooperation (Shoham & Tenneholz 1992; Jennings and Mandami 1992; Conte & Catselfranchi 1995; Jennings 1994; Walker & Wooldridge 1995).

Agents cannot be assumed to be benevolent

Why norms?

(a) How to avoid interferences and collisions among agents autonomously acting in a common space?

(b) How to ensure that negotiations and transactions fulfil the norm of reciprocity?

(c) How to obtain a robust performance in teamworks?

(d) How to prevent agents from dropping their commitments, or how to prevent agents from disrupting the common activity ?

Shoham & Tenneholz 1992

In multiagent systems be they human societies or distributed computing systems different agents, people or processes, aim to achieve different goals and yet these agents must interact either directly by sharing information and services or indirectly by sharing system resources. In such distributed systems it is crucial that the agents agree on certain rules in order to decrease conflicts among them and promote cooperative behavior. Without such rules even the simplest goals might become unattainable by any of the agents or at least not efficiently attainable. Just imagine driving in the absence of traffic rules. These rules strike a balance between allowing agents sufficient freedom to achieve their goals and restricting them so that they do not interfere too much with one another

Shoham & Tenneholz 1992

They consider the possibility of limiting the agents to a subset of the original strategies of a given game thus inducing a subgame of the original one. They call such a restriction a social constraint if the restriction leaves only one strategy to each agent. Some social constraints are consistent with the principle of individual rationality in the sense that it is rational for agents to accept those assuming all others do as well.

Hard or soft constraints?

The distinction between hard and soft constraints corresponds to the distinction between preventative and detective control systems. In the former a system is built such that violations are impossible (you cannot enter metro station without a ticket) or that violations can be detected (you can enter train without a ticket but you may be checked and sanctioned).

Autonomous agents

• Agents: systems oriented to achieve states in the world.

• Goal: an explicit representation of a world state which the agent wants to be realised; agents with goals and beliefs are cognitive agents.

• Belief: a representation of the world that the agent holds true.

• Norm: an obligation on a set of agents to accomplish/abstain from a given action,– external: no mental representation – internal,

• Institution: a supra-individual system deliberately designed or spontaneously evolved to regulate agents’ behaviour.

• Autonomy: an agent is autonomous wrt

– its physical environment or – other agents in the same environment -> social autonomy.

• Goal-autonomy • Norm-autonomy

Autonomy

"...to pose a goal to oneself is something about which no external legislation can interfere...". An agent: "cannot undergo any obligation other than what he gives himself on his own. (...) only by this means it is possible to reconcile this obligation (even if it were an external obligation) with our will".

Kant (Die Metaphysik der Sitten, 1794)

Normative systems and

deontic logic

Normative systems

• “Sets of agents whose interactions are norm-governed; the norms prescribe how the agents ideally should and should not behave. [...]

Importantly, the norms allow for the possibility that actual behavior may at times deviate from the ideal, i.e., that violations of obligations, or of agents’ rights, may occur.”

(Jones & Carmo 2001)

Deontic logic

• von Wright, 1951: formal study of ought

• Deontic modalities besides alethic ones– “it is obligatory to see to it that x” inspired

to “it is necessary that x”– “it is permitted to see to it that x” inspired to

“it is possible that x”

Modal operator

• Op = it is obligatory that p• Pp = Op it is permitted that p• Fp = Op it is forbidden that p• Minimal system D:

– O(p q) (Op Oq)– O(p) Op

(I.e. Pp, obligatory implies permitted)– if |- α then |- Oα

(but not Op p like for knowledge: ideal is not real necessarily)

Conditionals and paradoxes

• Obligations are inherently conditional:“when you… you have to…”

• Different possibilities to define O(y|x)– x O(y)– O(x y)– NEC(x O(y))

• They all have counterintuitive results: paradoxes of deontic logice.g. contrary to duty O(kill) but O(gently|kill)

Anderson’s reduction I

• Reduction of deontic logic to alethic logic: “the intimate connection between obligations and sanctions in normative systems suggests that we might profitably begin by considering some penalty or sanction S, and define obligations as: p is obligatory if its falsity entails the sanction S”.

Anderson’s reduction II

• Formalization– O(p) = NEC(p S) S

• Problem: not all violations are sanctioned

• Reply of Anderson “S just means something bad or violation”

Dynamic logic

• Meyer, 1988: Deontic logic viewed as a variant of dynamic logic

• a is obligatory if the effect of not doing action a is that there is a violation:O(a) = [¬a] V

The agent perspective: normative multiagent systems

Social order I

Castelfranchi 2000: Social orders are patterns of interactions among interfering agents that allow the satisfaction of the interests of agents, such as values or shared goals that are beneficial for most or all of the agents

Agents delegate to the normative system their own shared goals which become the content of the obligations regulating the system

Social order II

For example, if agents delegate the goal to avoid accidents to the normative system, then the system may adopt the subgoal to drive on the right side of the street. This subgoal is the content of the obligation to regulate traffic. Agents adopt this goal since they contribute to the delegated goal, and they know other agents will adopt it too

Social control

Castelfranchi 2000: Social control “An incessant local (micro) activity of its units aimed at restoring the regularities prescribed by norms”.

Agents attribute to the normative system the ability to autonomously enforce the conformity of the agents to the norms

Violating norms

Probably, when one thinks about multiagent systems, one assumes that the agents stick to the obligation posed by the system. However, this assumption is not always realistic, so we must consider what happens with agents that must be motivated to respect an obligation. See heterogeneous multi-institutional agents, like the Grid.

Why violating norms

Nobody can avoid that norms - and in particular their instances - might be incoherent. There might be conflicts, and the agents should be able to manage these conflicts. Norms also cannot predict and successfully frame all possible circumstances. There might be some important event or fact to be handled, where no norm applies or some norm applies with bad results.

Instrumental norms

• Law scholars like Hart distinguish:– primary norms: prescription of behavior– instrumental norms: help the achievement

of primary norms. Directed towards the juridical system: sanctions, procedures for trials

– …

(deontic logic focussed on primary norms)

What do we learn from this?

• Mental attitudes like goals not only at the individual level: delegation of goals

• Normative systems: not only specification of ideal behavior of the system, but also active role

• Normative system has goals and does actions. Is it an agent?

The agent metaphor

• G.Lakoff: Role of metaphor in cognition to conceptualize reality which is not bodily grounded.

• An ontology of social reality should disclose the metaphorical mapping we use to understand social reality

• Can the agent metaphor be used for understanding social reality?

Intentional stance

• Dennet: attitudes like belief and desire are folk psychology concepts that can be fruitfully used in explanations of rational human behavior. For an explanation of behavior it does not matter whether one actually possesses these mental attitudes: we describe the behavior of an affectionate cat or an unwilling screw in terms of mental attitudes. Dennet calls treating a person or artifact as a rational agent the ‘intentional stance’.

The importance of us

• “The possibility of ascribing goals, beliefs, and actions to collectives relies on the idea that collectives can be taken to resemble persons. […] both factual and normative beliefs can be ascribed (somewhat metaphorically) to groups, both formal and informal, structured and unstructured.” Tuomela, 1995

Norms as mental attitudes(Boella and van der Torre)

• If a normative system is described as an agent with mental attitudes,thus norms are defined in terms of the conditional mental attitudes of the normative agent– obligations are goals (“ideal behavior”)– what about beliefs?

Input/Output Logics (Makinson & van der Torre)

• Let R Rul: a,..,d→x or (a,…d,x)

• Outi(R) is closure under set of rules

– Out1:SI Out2:SI,OR

– Out3:SI,CT Out4:SI,OR,CT

a→x

a,b→xSI

a,b→x a,b→xOR

a→x

a→b a,b→x CTa→x

•Outi+: Outi and ID

a→aID

Multiagent system

MAS=<A,X,G,E,>– A: set of agents– X: propositional variables– G: goal rules a,..,d→x

– E: effect rules a,..,d→x

: priority relation on goal rules

Xa: actions of agent a, Ga: goals of a

Normative MAS

NMAS=<A,X,G,E,,N,V,n>– n A the normative agent– N: a set of norms– V: norm description N x A → X

eg V(n,a)

Anderson’s reduction:

Obligation Oa(x,s|C) if– C, x → V(n,a) E– V(n,a) → s E

Alternative approach

• Violation is not an effect of the behavior, but an action of the normative system

• Analogously, the sanction is an action of the normative system (with a cost)

• Recognizing violations and sanctioning violations are goals of the normative system

Obligations Oa,NS(x,s|Y)

1. Y→x is goal of NS 2. Y,x → V(n,a) is goal of NS3. Y,V(n,a) → s is goal of NS4. Y → s is goal of agent a

Two actions:V(n,a) = violation by agent a of norm ns is a sanction

precondition

Hart: Instrumental norms

Michael Luck, Fabiola López y López

• Societies and Autonomous Agents.• How can autonomous agents be integrated

into societies regulated by norms? • What does an agent need to deal with

norms?• What does an agent evaluate before

dismissing a norm?• How are the goals of an agent affected by

social regulations?

Michael Luck, Fabiola López y López

• A formal structure of norms that includes the different elements that must be taken into account when reasoning about norms

• A formal basic representation of norm-based systems

• An analysis and formalisations of the kinds of norms that norm-based systems have

• An analysis of the dynamics of norms• The set of normative relationships that might

emerge by adopting, complying and dismissing norms

Norms dynamics

Issue Spread

Adoption

Activation

Reward

Compliance

Violation

Modification

Abolition

Sanction Non-sanction

Dismissal

Norms compliance

currentgoals

goals normative goals

hindered by

normative gs

benefited from

rewards

hindered by

punishments

Z specification

Z specification

Emergence of norms

Off-line design: In this approach, social laws are designed off-line, and hard-wired into agents (Shoham & Tennenholtz 1992b; Goldman & Rosenschein 1993; Conte & Castelfranchi 1993).

Emergence from within the system: (Shoham & Tennenholtz 1992a; Kittock 1993), a convention can ‘emerge’ from within a group of agents.

The first approach will often be simpler to implement, with a greater degree of control over system functionality. But not all the characteristics of a system are known at design time; not suited for open systems.

Conte, Castelfranchi, Dignum, 1998

• Social science: norms are emergent properties of utility driven behavior. (Binmore 1994)

• They survive if associated with monitoring and sanctioning (Axelrod 1987, Boyd 2003)

• Social science does not explain the decision process of autonomous agents

Norm acceptance

• Norms would not be respected if there were the sanction only: 90% of crimes are not punished

• Norms are respected since they are accepted

• They derive from goals delegated to the normative system

Autonomous norm acceptance

An agent is norm autonomous if it can: (a) recognise or not a norm as a norm (normative

belief formation); (b) argue whether a given norm concerns or not

its case; decide to accept the norm or not; (c) decide to comply or not with it

(obey or violate); (d) take the initiative of re issuing (prescribing) the

norm, monitoring, evaluating and sanctioning the others' behaviour relatively to the norm.

Goal Acceptance• Goal-acceptance= a special case of goal-generation:

social goal-filter.– IF x wants p, and– x believes that IF y obtains q – THEN x obtains p– THEN x wants that y obtain q.

• Autonomous agents accept a new goal iff they believe that it is a means for an old one.

• The value of a current goal p increases if agents (are led to) believe that p is – Instrumental to one more important (meta-)goal q, or more

(meta-)goals Q (instrumentality beliefs. These include beliefs about achievement costs).

– Probability of instrumental connection is higher than expected (probability beliefs, whose credibility increases as a function of credibility of sources. These include a different evaluation of feasibility).

– Endangered. Maintenance goals are more compelling than achievement ones (emergency beliefs).

Norm acknowledgement

Input = a candidate norm (external norm). An obligation in the form OyX( q), q = the norm, y = authority that issues the norm and X = the set of the norm subjects.

Output = possibly a normative belief. Several tests:evaluation of the c- norm: is it based on a recognised N?

evaluation of the source: Is agi entitled to issue N? This entails:is q within the domain of y 's competence?is the current context the proper context of q?is X within the scope of y 's competence?

evaluation of the motives: is q issued for agi 's personal motives?

The evaluation process is formalised as follows:BELx(OzU( r)) BELx(OzU( r) OyX( q)) (10)(OyX( q) BELx(auth(y,X,q,C)) BELx(mot(y,OK))) BELx(OyX( q)) (11)

Both lead to BELx(OyX( q)) The relation “auth”: y has authority to issue q on X in C.

The relation “mot”: y's motives are correct.

Acceptance (From Conte et al., 1998)

Is N-belief sufficient? No! Belief about instrumentality. Normative corollary of social autonomy: x will form a N-goal q iff it

believes that q is instrumental to a further goal:

BELx(OyX( q) INSTR(OBTX(q),p) GOALx(p|r)) N-GOALx(OBTX(q)|GOALx(p|r) r)

Important differences from the g-generation rule: the existence of a N-belief. But norms can be autonomously created: BELx(O(OyX( q)) INSTR(OBTX(q),p) GOALx(p|r)) N-GOALx(OBTX(q)|GOALx(p|r) r)

the form of the instrumental belief. But x may have internalised the

norm: BELx(OyX( q) INSTR(q,p) GOALx(p|r)) C-GOALx(q|GOALx(p|r) r)No N-conformity. We need:

BELx(BELy(OzX( q))) BELx(OzX( q))

BELx(N-GOALy(OBTX(q)| r) INSTR(OBTX(q),be_like(x,y)))

plus GOALx(be_like(x,y)|true)

So far...• Agents undergo social influence, that is they are

often implicitly or explicitly requested to accept new goals.

• Institutional influence is a special case of social influence.

• In both cases, autonomous agents accept new goals (including normative ones) only as means to achieve old ones.

• Questions– But what are the specific motives for accepting

influence and forming new goals?– What is their respective efficacy? Which type of

influence is more effective?

Motives for Acceptance• Trust (probability/emergency

belief)

• Acknowledgement

• Social Responsibility

– Don’t harm Material (e.g., passive smoking) Symbolic harm (break

institutional authority)

- Don’t give a bad example

Goal

(execute action)Emotions

Bel

(p of connection)

Bel

(instrumentality)

Norm

(acceptance)

Bel

(emergency)

Goal (old)

Goal

(execute action)

Norm (old)

Motives for Acceptance (cont’)

Incentives• Negative

– penalty– costs of action– obstacles

• Positive – side-goals

– meta-goals

Bel

(instrumentality) Norm

(acceptance)

Goal

(avoid penalty

Bel

(importance)Goal

(execute action)

Goal (old) Side-Goal

Bel

(importance)Goal

(execute action)

Meta-Goal Goal (old)

Motives for Acceptance (cont’)

• Social Control– Image and reputation

» Responsible» Rational, consistent» Trustworthy

– Social isolation

– Social identity

• Sharing (new) social norms & values

Bel

(instrumentality)Goal

(execute action)

Goal

(accept influence)

Goal (old)

Bel

(value or norm)Bel

(instrumentality

Norm or Value

(shared)

Goal

(execute action

The construction of social reality

John Searle

“Consider a simple scene like the following. I go into a café in Paris and sit in a chair at a table. The waiter comes and I utter a fragment of a French sentence. I say, "un demi, Munich, à pression, s'il vous plaît." The waiter brings the beer and I drink it. I leave some money on the table and leave. … [Notice] that the scene as described has a huge, invisible ontology: the waiter did not actually own the beer he gave me, but he is employed by the restaurant which owned it. The restaurant is required to post a list of the prices of all the boissons, and even if I never see such a list, I am required to pay only the listed price. The owner of the restaurant is licensed by the French government to operate it. As such, he is subject to a thousand rules and regulations I know nothing about. I am entitled to be there in the first place only because I am a citizen of the United States, the bearer of a valid passport, and I have entered

France legally.” p.3

John Searle

• According to Searle we live in and we are surrounded by a different kind of reality constructed by humans

• How is it constructed?

A Two-Levelled Ontology

In The Construction of Social Reality, John Searle argues for a two-level ontology along the following lines. Facts on the lower level - which he calls brute facts - can exist independently of human beings and their institutions. Facts on the upper level, which he calls institutional facts, depend on institutions and on an associated 'collective intentionality'. The existence of Planet Earth is a brute fact, the existence of Utah is an institutional fact.

As Searle confesses, there is a sort of magic involved when 'we impose rights, responsibilities, obligations, duties, privileges, entitlements, penalties, authorizations, permissions ... in order to regulate relations between people'

Searle’s construction of social reality

• “Some rules regulate antecedently existing forms of behaviour. For example, the rules of polite table behaviour regulate eating, but eating exists independently of these rules. Some rules, on the other hand, do not merely regulate an antecedently existing activity called playing chess; they, as it were, create the possibility of or define that activity. The activity of playing chess is constituted by action in accordance with these rules. Chess has no existence apart from these rules. The institutions of marriage, money, and promising are like the institutions of baseball and chess in that they are systems of such constitutive rules or conventions.

Counts as

For Searle, institutional facts like marriage, money and private property emerge from an independent ontology of “brute” physical facts through constitutive rules of the form“such and such an X counts as Y in context C” where X is any object satisfying certain conditions and Y is a label that qualifies X as being something of an entirely new sort. E.g., “X counts as a presiding official in a wedding ceremony”, “this bit of paper counts as a five euro bill” and “this piece of land counts as somebody’s private property”.

Constitutive vs regulative norms

• Two types of norms: – regulative norms: obligations, prohibitions,

permissions– constitutive norms: provide a legal

classification of reality – institutional facts: legal categories

Institutionalized powerJones & Sergot 1996

It is a standard feature of norm governed institutions that designated agents are empowered to create particular kinds of states of affairs by means of the performance of specified types of actions. Frequently, the states of affairs are of a normative kind, in the sense that they pertain to rights and obligations, as for instance when a Head of Department signs a purchase agreement and thereby creates an obligation on his employer to pay for goods received.

Means of powers

The performances by means of which these states are established will often be of a clearly prescribed, perhaps ritualised nature, involving the utterance of a particular form of words (e.g., the utterance of a specific type of performative sentence), or the production of a formal document, or the issuing of a pass, perhaps in a particular context (e.g., in the presence of witnesses).

Definition of powers I

Within institutions, organisations, or other normative systems, there operate constraints to the effect that the performance by some specified agent x of some designated action is sufficient condition to guarantee that some specified agent y creates some (usually normative) state of affairs F. The agent y might be identical with the agent x, but this need not always be so.

Definition of powers II

Often it would be appropriate to say that the agent y who creates the state of affairs F is the institution or normative system itself; for instance, it may be the registrar or priest who plays the role of x, performing the marriage ceremony, but it is the legal system or church which creates the normative relation of being married. We are thus led to focus on statements of the following kind: ``According to normative system/institution s, if agent x sees to it that A then agent y sees to it that F”

Ex A ==>s Ex Fwhere Ex A to stand for ``x sees to it that/brings it about

that A'‘

Real example

The United Nations Convention on Contractsfor the International Sale of Goods (1980)Article 15(1) An offer becomes effective when it reaches theofferee.(2) An offer, even if it is irrevocable, may be withdrawn ifthe withdrawal reaches the offeree before or at thesame time as the offer.Article 63(1) The seller may fix an additional period of time ofreasonable length for performance of the buyer of hisobligation…

Counts as

Powx (F;A) = Ex A ==>s Ex Fa conditional connective

A ==>s B: A counts as B (in institution s)

properties

(A ==>s B /\ A ==>s C)-> A ==>s (B /\C)

(A ==> s B /\ C ==>s B)-> (A\/C) ==>s B

Monotony?

Makinson 1986

Consider the case of a priest of a certain religion who does not have permission, according to instructions issued by the ecclesiastical authorities, to marry two people, only one of whom is of that religion, unless they both promise to bring up the children in that religion. He may nevertheless have the power to marry the couple even in the absence of such a promise, in the sense that if he goes ahead and performs the ceremony, it still counts as a valid act of marriage under the rules of the same church even though the priest may be subject to reprimand or more severe penalty for having performed it.

Makinson: meanings of power

permissionto exercisethis power

institutionalisedpower/competence

(‘authority’)

ability

to exercise

this power

Normative systems as agents

• If the normative systems can be described as an agent: it has goals and beliefs

• In Boella and van der Torre’s model, obligations are defined as goals of the agents.

What corresponds to the normative system’s beliefs?

Constitutive norms as beliefs

• If constitutive norms provide a legal classification of reality, they can be considered as the beliefs of the normative agent.

• x Counts As y in C: C,x → y is a belief of NS– y is an institutional fact– x is a “brute fact” or an institutional fact– C is the context

Beyond Searle’s constitutive norms

• Changing the normative system

• Hart: private citizens becomes legislators

• Constitutive norms specify how the system can be changed by itself or by other agents