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Topic 5: Communication and Negotiation Protocols
Communication and ACLs direct vs. indirect communication speech act theory ACLs - KQML / FIPA-ACL
Negotiation protocols contract-net protocol auction protocols
Notation - AUML
1. Communication and ACLs
BlackboardBlackboard
AgentAgent
AgentAgent
AgentAgent
AgentAgent
AgentAgent
AgentAgent
Indirect communication information available for all no direct communication simple architecture
communication the basis for any interaction “effected through signals”
Agent A (Sender)Agent A (Sender)
Agent B (Receiver)Agent B
(Receiver)
Message
Message passing direct exchange common language conversation - sequences of
messages
Direct communication
message passing some of the challenges
distributed systems brokering, naming services, discovery, … “infrastructure” for sending messages heterogeneous entities
language, developer, execution environment, …
multi-agent systems objects messages
agents speech acts
why something different?
an example
MAS with cognitive of practical reasoning agents
focus on mental states “messages must have a meaning to other agents”
e.g. “agent 1 sends message to agent 2: doSomething(x)”
what does this mean to agent 2 ? how should/could he respond ? agent 1 asks agent 2 to do x ? – part of negotiation protocol … ? agent 1 tells agent 2 to do x ? – assuming a commitment … ? agent 1 relies on the fact that agent 2 will do x ?
– part of task allocation … ?
agent 1 will do x ? does agent 2 think agent 1 is waiting for a reply ? what is x ? a task ? a question ? the name of an agent ? does agent 1 asks agent 2 to perform task itself, or just make sure the
result is achieved what must agent 2 do with the result ?
must be semantically clear heterogeneity, openness, …
consequence agents must be endowed with capabilities to understand and reason upon the
meaning and content of messages”
Agent Communication
ability to exchange information requires
1. ability to “physically” exchange information
2. common understanding
3. common language
4. interaction strategies / protocols
Agent Communication
ability to exchange information requires 1. ability to “physically” exchange information
2. common understanding
3. common language
4. interaction strategies / protocols
high-levelcommunication
low-levelcommunication
(tcp-ip, http, smtp, …)
Agent Communication
ability to exchange information requires
1. ability to “physically” exchange information 2. common understanding
exchanging knowledge requires mutual understanding 2 keys
translation between languages sharing semantic content
- each agent has implicit assumptions on its own semantics
- translation must preserve semantics!
to share knowledge, we must have a common semantics
can be shared via “common ontologies”
3. common language 4. interaction strategies / protocols
Agent Communication
ability to exchange information requires
1. ability to “physically” exchange information
2. common understanding
3. common language
incorporates two types of languages
content language
communication language
Agent Communication Language
4. interaction strategies / protocols
Agent Communication Languages (ACL)
Agents are typically defined at a “high” level
an ACL should support intentional communication
the intentional descriptions use concepts such as: beliefs,goals, intentions, commitment
the language should not define protocols such as
transport protocols high level coordination protocols constraints on valid exchanges
Speech Act Theory
speech act theory views human speech actions (John Austin, 1962) as in “an attempt to influence …”
three parts of speech locution physical utterance illocution the intended meaning perlocution the action that results from the locution
use performatives to identify illocutionary force
example:
“Please be quiet!” locution – the actual performance of the act
illocution – the purpose of the utterance
perlocution – the consequences of the utterance
ACLs: FIPA ACL
Foundation for Intelligent Physical Agents - http://www.fipa.org/
o 1995 since 2005: IEEE Computer Society standards organization “promotes agent-based technology and the interoperability of its standards with
other technologies”
standardisation of agent-related issues FIPA-OS FIPA infrastructure architecture ... FIPA-ACL
similar to KQML consists of a set of message types and the description of their pragmatics — that is, the effects
on the mental attitudes of the sender and receiver agents. describes every communicative act with both a narrative form and a formal semantics based on
modal logic. separates the outer language (the intended meaning of the message) from the inner language
(content language).
ACL Message
(inform :sender agent1 :receiver hpl-auction-server (price (bid good02) 150) :in-reply-to round-4 bid04 :language sl :ontology hpl-auction)
:content
:reply-with
performative
content
comm.information
FIPA ACL: semantics in SL“the Semantic Language”
SL (Semantic Language) can represent propositions, objects, and actions
formal semantics
< message ; precondition ; rational effect >
message the content of the message precondition on the “situation” (mental state) of the sender rational effect intended effect on mental state of receiver
FIPA - Communicative Acts (1)
inform the sender informs the receiver that a given proposition is true.
confirm the sender informs the receiver that a given proposition is true, where the receiver is
known to be uncertain about the proposition. disconfirm
the sender informs the receiver that a given proposition is false, where the receiver is known to believe, or believe it likely that, the proposition is true.
failure the action of telling another agent that an action was attempted but the attempt failed
accept-proposal the action of accepting a previously submitted proposal to perform an action
agree the action of agreeing to perform some action, possibly in the future
cancel the action of cancelling some previously request'ed action which has temporal extent
(i.e. is not instantaneous) cfp
the action of calling for proposals to perform a given action.
FIPA - Communicative Acts (2)
inform-if a macro action for the agent of the action to inform the recipient whether or not a
proposition is true. inform-ref
a macro action for sender to inform the receiver that an object corresponds to a definite descriptor (e.g. a name).
not-understood the sender of the act (e.g. i) informs the receiver (e.g. j) that it perceived that j
performed some action, but that i did not understand what j just did. propose
the action of submitting a proposal to perform a certain action, given certain preconditions.
query-if the action of asking another agent whether or not a given proposition is true.
query-ref the action of asking another agent for the object referred to by an expression.
refuse the action of refusing to perform a given action, and explaining the reason for the
refusal.
FIPA - Communicative Acts (3)
reject-proposal the action of rejecting a proposal to perform some action during a negotiation.
request the sender requests the receiver to perform some action. One important class of
uses of the request act is to request the receiver to perform another communicative act.
request-when the sender wants the receiver to perform some action when some given
proposition becomes true. request-whenever
the sender wants the receiver to perform some action as soon as some proposition becomes true and thereafter each time the proposition becomes true again.
request-whomever the sender wants an action performed by some agent other than itself. The
receiving agent should either perform the action or pass it on to some other agent. subscribe
the act of requesting a persistent intention to notify the sender of the value of a reference, and to notify again whenever the object identified by the reference changes.
ACLs: KQML Knowledge Query Manipulation Language (KQML)
KQML has 3 layers
content - ignored by KQML messages
message determines interaction types supplies performative & content may describe ontology, etc.
communication low level communication parameters sender, receiver, unique message ID
1. Communication – ACLs
2. Negotiation protocols
Basic protocols
contract-net protocol auction protocols
Negotiation protocols /Market-based Mechanisms
… iterative communication among a group of agents in order to reach a mutually accepted agreement on something…..
every day approach in resolving conflicts
needed: a set of options a utility function
every option has a price and benefit this function evaluates the worth of an option to an agent.
a negotiation protocol multiple stages or steps in the negotiation process eventually the process must either terminate or converge to a solution
The Contract Net Protocol
introduced by R.G.Smith in 1980 studied extensively with several variations in subsequent years.
how it works a manager
breaks the problem into several interacting sub-problems looks for a contractor selects the suitable contractor assigns a sub-problem monitors the progress of the overall solution
a contractor ‘bids’ for work accepts a task it has a binding agreement to complete the task according to the agreed terms
and completes the task undertaken.
recursively, the contractor can be a manager for the task it has undertaken.
Basic assumptions: the problem has a well defined structure for decomposing coarse-grain decomposition is possible there are enough contractors waiting to do the announced tasks
The Contract Net Protocol
I have a problem!
(a) Recognising the problem
managerPotentialcontrators
announcement
(b) Task Announcement
manager
bids
(c) Bidding
manager
Award task Potentialcontrator
(d) Award Contract
Applicability of Contract Net
The Contract Net is a high-level communication protocol a way of distributing tasks dynamically decentralized / situated a means of self-organization for a group of agents
but limited (mostly for well-defined hierarchies of tasks) not scalable re-allocation ?
Auctions
an auction takes place between an agent known as the auctioneer a collection of agents known as the bidders
goal: for the auctioneer to allocate the good to one of the bidders
typically the auctioneer desires to maximize the price bidders desire to minimize price
Auction Parameters
goods can have private value public / common value correlated value
winner determination may be first price second price
bids may be open cry sealed bid
bidding may be one shot ascending descending
Example Auction protocols
English auction parameter values
first price open cry ascending
Dutch auction parameter values
open-cry descending (first price)
First-Price Sealed-Bid Auctions parameter values
sealed bid one-shot auction first price
…
4. Notation - Agent UML
a proposal for an agent-oriented modeling language Pros:
Likely standardization on UML 2.0 Accepted by FIPA
Contras: UML dialect, not necessarily compatible
AUML AUML class diagram AUML interaction diagrams
esp. AUML sequence diagrams
http://www.fipa.org/repository/ips.php3
FIPA TC C 2000Specifies 11 Protocol Specifications
http://www.fipa.org/repository/ips.php3
1. FIPA Request Interaction Protocol Specification
2. FIPA Query Interaction Protocol Specification
3. FIPA Request When Interaction Protocol Specification
4. FIPA Contract Net Interaction Protocol Specification
5. FIPA Iterated Contract Net Interaction Protocol Specification
6. FIPA English Auction Interaction Protocol Specification
7. FIPA Dutch Auction Interaction Protocol Specification
8. FIPA Brokering Interaction Protocol Specification
9. FIPA Recruiting Interaction Protocol Specification
10. FIPA Subscribe Interaction Protocol Specification
11. FIPA Propose Interaction Protocol Specification