A Context-based Institutional Normative Environment Henrique Lopes - - PowerPoint PPT Presentation
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LIACC, DEI / Faculdade de Engenharia, Universidade do Porto {hlc, eco}@fe.up.pt
May 12th 2008, COIN@AAMAS’08
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A common normative structure for several social
systems
first the EI, then the specific “environments”
(contexts) Adaptability of the normative environment to each
context
agents exploit and adapt the normative
environment to fit their purposes Situated
couple an EI with a previously existing
environment (social system) Autonomic
autonomous adaptation of the social system’s
rules to enhance performance
“A Context-Based Institutional Normative Environment” “Formalising Situatedness and Adaptation in Electronic Institutions”
“Specialization” of norms as an inheritance
preventing mechanism
not necessarily more restricted in that sense
Norm monitoring model
enables objective centralized reputation service
Organizational Norms (ON) vs. Individual Norms
(IN)
IN are specializations of ON IN are more restricted than ON
(De)centralized hybrid reputation model
collection of distributed evaluations quality of reputation source
“A Context-Based Institutional Normative Environment” “A Hybrid Reputation Model Based on the Use of Organizations”
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Normative environment Contexts and normative state Rules and semantics of
Norms, defeasible norm
Example Conclusions
Top Context
N1 N2 N3 N4 N5 N6 N7
Context G1
N1 N2 N8
Normative Framework Context B1
N4’ N3 N5
Context B2
N3 N5 N4
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EI = Services + Normative Environment
Services
assist agents in contract establishment contracts can be underspecified, relying on a normative framework
Normative Environment NE =
facts, obligations, fulfillments, violations, time
Institutional Rules IR
maintain the normative state by defining interrelations among its elements
Norms N
define the normative positions of each agent in the system
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within which a set CA of agents commits to a joint activity partially regulated by CN ⊆
⊆ ⊆ ⊆ N
CI is a set of founding contextual info PC is the parent context within which C is formed
Each Contract generates a Context
C’ is a sub-context of C =
C’
C’
Motivation: a B2B contractual agreement C forms a business-context for a
more specific contract C’
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Contextual info InfoC ∈
fully-grounded atomic formula in FOL Motivation: a contract contains intrinsic information defining it (roles,
exchanged values, provisions)
Normative State NS = {IRE1
C1, IRE2 C2, …, IREn Cm,}
each institutional reality element IREi
Cj is a fully-grounded atomic
formula in FOL
ifactC(f, t) – institutional fact timeC(t) – time
fulfC(a, f, t) – fulfillment violC(a, f, t) – violation
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Semantics of rules: substitution in FOL
substitution Θ
Θ Θ Θ matches Antecedent with NS
apply Θ
Θ Θ Θ to Consequent and add fully-grounded atomic formulae to NS
Use-case: implement the semantics of deadline obligations Rule R ::= Antecedent → → → → Consequent
IREC ¬ ¬ ¬ ¬ < < < < ≤ ≤ ≤ ≤ = = = = ≥ ≥ ≥ ≥ > > > > IRE-C
∧ ∧ ∧ ∧ ∧ ∧ ∧ ∧
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fulfillment only if no violation:
need for rule evaluation after each NS update relaxing this need: use IRE’s time references
temporal deadlines
p B q : p before q Gq : henceforth q p @ q : ¬(p B q) ∧ ¬(q B p)
ifact B time
time B ifact ifact @ time
X holds if (time B ifact) !
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Norm NC is
defined in context C applicable to C or to a sub-context C’
Two kinds of elements in the Situation:
background (Sb): exist at context creation – InfoC’ contingent (Sc): added later to the normative state – IRE-C’
Norm NC ::= Situation → → → → Prescription
IRE-C’ InfoC’
< < < < ≤ ≤ ≤ ≤ = = = = ≥ ≥ ≥ ≥ > > > > ∧ ∧ ∧ ∧ ∧ ∧ ∧ ∧ C’
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Norm activation Norm activation conflict
Act1 ⊗
⊗ ⊗ ⊗ Act2 if NS1 = NS2 and either C1
Norm activation defeasance
Act1 defeats Act2 if Act1 ⊗
⊗ ⊗ ⊗ Act2 and C1
NC = Sb ∧ ∧ ∧ ∧ Sc ∧ ∧ ∧ ∧ … → → → → P applicable to C’ =
∀ ∀ ∀c∈
∈ ∈ ∈Sc c⋅
⋅ ⋅ ⋅Θ Θ Θ Θ ∈ ∈ ∈ ∈ NS ∀ ∀ ∀ ∀b∈
∈ ∈ ∈Sb b⋅
⋅ ⋅ ⋅Θ Θ Θ Θ ∈ ∈ ∈ ∈ CI’ subst Θ Θ Θ Θ contingent facts activation substitution norm NS2 = {c⋅ ⋅ ⋅ ⋅Θ Θ Θ Θ2 | c∈ ∈ ∈ ∈Sc2} Act2 Θ Θ Θ Θ2 N2
C2 = Sb2 ∧
∧ ∧ ∧ Sc2 ∧ ∧ ∧ ∧ … → → → → P2 NS1 = {c⋅ ⋅ ⋅ ⋅Θ Θ Θ Θ1 | c∈ ∈ ∈ ∈Sc1} Act1 Θ Θ Θ Θ1 N1
C1 = Sb1 ∧
∧ ∧ ∧ Sc1 ∧ ∧ ∧ ∧ … → → → → P1
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Norms may pre-exist to the contexts to which they apply Norm applicability
from a sub-context to a range of sub-contexts
typify contexts: C’ = id:type
NC = S →
→ → → P
patterns of InfoC’ and IREC’ in S and P: InfoX:t, IREX:t
unbound variable X: match Info’s and IRE’s of any sub-context of type t
substitution Θ
Θ Θ Θ binds X to a specific sub-context
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Supply-agreement: sa context type
top context norm sub-context: sa3:sa
InfoX:sa IREX:sa
jim Qt > 99 jim 5 sam fulf sam sam
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Conflict NS none, N1
top applies
ifactsa3:sa(order(tom, r1, 5, jim), 1) N1
sa3:sa defeats N1 top
ifactsa3:sa(order(tom, r1, 100, jim), 1) N2
sa3:sa defeats N1 top
ifactsa3:sa(order(sam, r3, 5, tom), 1) none, N3
sa3:sa applies
ifactsa3:sa(order(sam, r3, 5, tom), 1)
fulfsa3:sa(tom, delivery(tom, r3, 5, sam), 2)
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Normative Framework
initial aim is not to impose, but to assist building contracts through a
normative background
adapt normative framework as needed (all norms are defeasible) created contracts are then enforced
Defeasible norm activations
conflict based on the applicability conditions, not the deontic
conclusions
(norm defeasibility is typically based on deontic conflicts)
Lex superior, posterior, specialis
“lex inferior” with a lex specialis flavor?
Future Work
non-defeasible norms