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.
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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
(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 ?
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
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.
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).
"...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 anddeontic logic
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)
(but not Op p like for knowledge: ideal is not real necessarily)
The agent perspective: normative multiagent systems
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
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
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
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.
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.
(deontic logic focussed on primary norms)
Xa: actions of agent a, Ga: goals of a
Obligation Oa(x,s|C) if
V(n,a) = violation by agent a of norm n
s is a sanction
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.
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.
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.
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)))
(p of connection)
Goal (old) Side-Goal
Meta-Goal Goal (old)
(value or norm)
Norm or Value
The construction of social reality
“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 leavesome 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
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'
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”.
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.
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).
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.
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”
ExA ==>s ExF
where Ex A to stand for ``x sees to it that/brings it about that A'‘
The United Nations Convention on Contracts
for the International Sale of Goods (1980)
(1) An offer becomes effective when it reaches the
(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.
(1) The seller may fix an additional period of time of
reasonable length for performance of the buyer of his
Powx (F;A) = ExA ==>s ExF
a conditional connective
A ==>sB: A counts as B (in institution s)
(A ==>sB /\ A ==>sC)-> A ==>s (B /\C)
(A ==> sB /\ C ==>s B)-> (A\/C) ==>sB
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.
What corresponds to the normative system’s beliefs?