Plan of the tutorial

1
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

2
Introduction
3
Social norms

• In the MultiAgent 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

4
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 ?

5
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

6
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.

7
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).

8
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 -gt
  social autonomy.
• Goal-autonomy
• Norm-autonomy

9
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)

10
Normative systems anddeontic logic
11
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)

12
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

13
Modal operator

• Op it is obligatory that p
• Pp ?O?p it is permitted that p
• Fp O?p it is forbidden that p
• Minimal system D
• O(p ? q) ? (Op ? Oq)
• O(p) ? ?O?p (I.e. Pp, obligatory implies
  permitted)
• if - a then - Oa
• (but not Op ? p like for knowledge ideal is not
  real necessarily)

14
Conditionals and paradoxes

• Obligations are inherently conditionalwhen
  you you have to
• Different possibilities to define O(yx)
• 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(gentlykill)

15
Andersons 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.

16
Andersons 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

17
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 violationO(a) a V

18
The agent perspective normative multiagent
systems
19
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

20
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

21
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

22
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.

23
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.

24
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)

25
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?

26
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?

27
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.

28
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

29
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?

30
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
• Out1SI Out2SI,OR
• Out3SI,CT Out4SI,OR,CT

a?x
a,b?x a,?b?x
a?b a,b?x
CT
SI
OR
a,b?x
a?x
a?x

• Outi Outi and ID

ID
a?a
31
Multiagent system

• MASltA,X,G,E,?gt
• 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

32
Normative MAS

• NMASltA,X,G,E,?,N,V,ngt
• n ? A the normative agent
• N a set of norms
• V norm description N x A ? Xeg V(n,a)
• Andersons reduction
• Obligation Oa(x,sC) if
• C, ?x ? V(n,a) ? E
• V(n,a) ? s ? E

33
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

34
Obligations Oa,NS(x,sY)

• Y?x is goal of NS
• Y,?x ? V(n,a) is goal of NS
• Y,V(n,a) ? s is goal of NS
• Y ? ?s is goal of agent a
• Two actions
• V(n,a) violation by agent a of norm n
• s is a sanction

Hart Instrumental norms
precondition
35
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?

36
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

37
Norms dynamics
Issue
38
Norms compliance
current goals
benefited from rewards
hindered by punishments
39
Z specification
40
Z specification
41
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.

42
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

43
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

44
Autonomous norm acceptance

• An agent is normautonomous 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 reissuing
  (prescribing) the norm, monitoring, evaluating
  and sanctioning the others' behaviour relatively
  to the norm.

45
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).

46
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.

47
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(pr))
  ? N-GOALx(OBTX(q)GOALx(pr) 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(pr))
• 
  ? N-GOALx(OBTX(q)GOALx(pr) r)
  
• the form of the instrumental belief. But x
  may have internalised the norm
• BELx(OyX( q) INSTR(q,p) GOALx(pr)) ?
  C-GOALx(qGOALx(pr) r)No N-conformity. We
  need
• BELx(BELy(OzX( q))) ? BELx(OzX( q))
  
• BELx(N-GOALy(OBTX(q) r) ? INSTR(OBTX(q),be_li
  ke(x,y)))
• plus GOALx(be_like(x,y)true)
  

48
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?

49
Motives for Acceptance
Goal (old)

• Trust (probability/emergency belief)
• Acknowledgement
• Social Responsibility
• Dont harm
• Material (e.g., passive smoking)
• Symbolic harm (break institutional authority)
• Dont give a bad example

Bel (p of connection)
Goal (execute action)
Emotions
Norm (acceptance)
Bel (instrumentality)
Bel (emergency)
50
Motives for Acceptance (cont)

• Incentives
• Negative
• penalty
• costs of action
• obstacles
• Positive
• side-goals
• meta-goals

51
Motives for Acceptance (cont)
Goal (old)

• Social Control
• Image and reputation
• Responsible
• Rational, consistent
• Trustworthy
• Social isolation
• Social identity
• Sharing (new) social norms values

Goal (accept influence)
Bel (instrumentality)
Goal (execute action)
Bel (value or norm)
Norm or Value (shared)
Bel (instrumentality
Goal (execute action
52
The construction of social reality
53
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

54
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?

55
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'

56
Searles 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.

57
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 formsuch 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 somebodys private property.

58
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

59
Institutionalized powerJones Sergot 1996

• It is a standard feature of normgoverned
  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.

60
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).

61
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.

62
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 gts Ex F
• where Ex A to stand for x sees to it
  that/brings it about that A'

63
Real example

• The United Nations Convention on Contracts
• for the International Sale of Goods (1980)
• Article 15
• (1) An offer becomes effective when it reaches
  the
• offeree.
• (2) An offer, even if it is irrevocable, may be
  withdrawn if
• the withdrawal reaches the offeree before or at
  the
• same time as the offer.
• Article 63
• (1) The seller may fix an additional period of
  time of
• reasonable length for performance of the buyer of
  his
• obligation

64
Counts as

• Powx (FA) Ex A gts Ex F
• a conditional connective
• A gts B A counts as B (in institution s)
• properties
• (A gts B /\ A gts C)-gt A gts (B /\C)
• (A gt s B /\ C gts B)-gt (A\/C) gts B
• Monotony?

65
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.

66
Makinson meanings of power
institutionalised power/competence (authority)
ability to exercise this power
permission to exercise this power
67
Normative systems as agents

• If the normative systems can be described as an
  agent it has goals and beliefs
• In Boella and van der Torres model, obligations
  are defined as goals of the agents.
• What corresponds to the normative systems
  beliefs?

68
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

69
Beyond Searles 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