1. 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

2. 1. Communication and ACLs
the basis for any interaction
“effected through signals”
Blackboard
Agent
Indirect communication
information available for all
no direct communication
simple architecture
Agent A
(Sender)
Agent B
(Receiver)
Message
Message passing
direct exchange
common language
conversation - sequences of messages

3. 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?

4. 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”

5. Agent Communication ability to exchange information requires
1. ability to “physically” exchange information
2. common understanding
3. common language
4. interaction strategies / protocols

6. Agent Communication ability to exchange information requires
1. ability to “physically” exchange information
2. common understanding
3. common language
4. interaction strategies / protocols
high-level
communication
low-level
(tcp-ip, http, smtp, …)

7. 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

8. 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

9. 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

10. Speech Act Theory “Please be quiet!”
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

11. ACLs: FIPA ACL
Foundation for Intelligent Physical Agents -
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).

12. ACL Message performative content comm.information ( 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
comm.information
content

13. FIPA ACL: performatives

14. 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

15. 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.

16. 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.

17. 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.

18. 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

19. 1. Communication – ACLs 2. Negotiation protocols
Basic protocols
contract-net protocol
auction protocols

20. 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

21. 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

22. The Contract Net Protocol
I have a problem!
manager
Potential
contrators
announcement
(b) Task Announcement
(a) Recognising the problem
manager
bids
manager
Award task
Potential
contrator
(c) Bidding
(d) Award Contract

23. The Contract Net Protocol
ACL messages

24. 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 ?

25. Auctions an auction takes place between goal: typically
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

26. Auction Parameters goods can have winner determination may be
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

27. Example Auction protocols
English auction
parameter values
first price
open cry
ascending
Dutch auction
open-cry
descending
(first price)
First-Price Sealed-Bid Auctions
sealed bid
one-shot auction …

28. English Auctions

29. Dutch Auctions

30. 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

31. FIPA TC C 2000 Specifies 11 Protocol Specifications
FIPA Request Interaction Protocol Specification
FIPA Query Interaction Protocol Specification
FIPA Request When Interaction Protocol Specification
FIPA Contract Net Interaction Protocol Specification
FIPA Iterated Contract Net Interaction Protocol Specification
FIPA English Auction Interaction Protocol Specification
FIPA Dutch Auction Interaction Protocol Specification
FIPA Brokering Interaction Protocol Specification
FIPA Recruiting Interaction Protocol Specification
FIPA Subscribe Interaction Protocol Specification
FIPA Propose Interaction Protocol Specification

32. Summary communication ACLs --> speech act theory
indirect (later) vs. direct communication
message-based communication
ACLs --> speech act theory
Negotation protocols
Notation - AUML