AOSE

1
AOSE

• Advanced Software Engineering
• University College Dublin
• December 2007
• Dr Rem Collier

2
AOSE

• Introduction to Agent Interaction

3
Agents and Interaction

• Interaction forms the basis of an agents
  collaborative problem solving capabilities.
• Agents are designed to operate in tandem with one
  another.
• This includes sharing and requesting knowledge,
  negotiating services, coordinating activities,
• Key to realisation of such activities is the
  implementation of an underlying communication
  mechanism.
• Two broad approaches to communication
• Shared space communication
• Communication by message passing

4
Shared Space Communication

• General Principle
• All agents of the MAS have access to a common
  area of memory (the shared memory).
• This access allows both for reading and writing.
• If an agent writes information to this area
  (often also called blackboard) every other agent
  can read it.
• This realizes a 1m communication and each agent
  has to decide on its own what to do with such an
  information
• ignore it
• use it
• delete it (usually forbidden)

5
Shared Space Communication

• General Principle
• It is quite often layered, with each layer
  representing a differing degree of abstraction
  for the current problem.
• Any agent working at some level on the blackboard
  has access to that complete level along with all
  adjacent levels.
• This allows data synthesised a lower levels to be
  communicated to higher levels, and for
  higher-level goals to be filtered down to lower
  level agents.

6
Example JavaSpaces

• JavaSpaces is a service specification that
  provides a distributed object exchange and
  coordination mechanism.
• Part of the Jini Project
• Originally developed by Sun.
• Now open-source as Apache River.
• Targeted at distributed systems development.
• Not really an agent solution, although
  Coordination Languages are seen as agent
  friendly.
• Whn connected to a JavaSpaces infrastructure, a
  process can
• write an object into a JavaSpace
• take an object from a JavaSpace
• make copies of objects from a JavaSpace

7
Example JavaSpaces

• Features
• Spaces are persistent.
• When you store an object in a space, it will
  remain there indefinitely until it is removed.
• You can also request a lease time during which an
  object should be stored.
• Once stored in the space, an object will remain
  there until its lease time (which can be renewed)
  is over, or until a process explicitly removes
  it.
• Spaces are associative.
• Objects in a space are located via associative
  lookup, not by memory location or by identifier.
• To look up an object, you create a template (an
  object with some or all of its fields set to
  specific values, and the others left as null to
  act as wildcards).
• An object in the space matches a template if it
  matches the template's specified fields exactly.

8
Example JavaSpaces

• Features
• Spaces are transactionally secure.
• JavaSpaces makes use of Jini's transaction
  service to ensure that an operation on a space is
  atomic (either the operation is applied, or it
  isn't).
• Spaces let you exchange executable content.
• While in a space, objects are just passive data.
• When you read or take an object from a space, a
  local copy of the object is created.
• As with any other local object, you can modify
  its public fields and invoke its methods, even if
  you've never seen an object like it before.

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Shared Space Communication

• Advantages
• Extensibility All agents communicate via the
  shared space.
• Clearly defined interface.
• Supports visualisation of global agent
  interactions.
• Supports easy decomposition and distribution of
  problems.
• Disadvantages
• Information Overload Must consider ALL messages.
• Potential Bottleneck / Single Point of Failure.
• Can be overcome by implementing a virtual shared
  space gt network overhead.
• Loss of privacy

10
Communication byMessage Passing

• General Principle
• Communication takes place through the
  transmission of messages directly between two
  agents (11 communication).
• Both agents have to perform (nearly)
  simultaneously communication actions
• The sender sends the message composed by it to
  some communication channel.
• The receiver gets the message from that channel.
• Usually the message is composed in a special
  communication language that has to be understood
  by both agents.
• Interaction normally consist of several messages
  where the agents take their turns as sender and
  receiver.
• This is called a dialog or a protocol.

11
Communication byMessage Passing

• Advantages
• Well suited to internet scale applications.
• Communication is directed to relevant agents (no
  information overload).
• More Robust So long as the communication channel
  is decentralised.
• Disadvantages
• Agent Discovery new agents must register their
  existence.
• Choosing an appropriate communication language.
• Defining and enforcing protocols.

12
Example Agent Factory

• Agents communicate by passing messages in an
  underlying Agent Communication Languages.
• Messages have types inform, request,
• Messages have inner content What activity is
  being requested / what information is being
  given.
• Agents send messages by performing an action.
• This action constructs the underlying message and
  selects an appropriate communication channel.
• Agents receive messages via perception of a
  private message queue.
• The communication channel routes messages to a
  private message queue of the receiver agent.
• The agent then perceives the message via a
  perceptor.

13
AOSE

• Towards Agent Interaction

14
Agent Communication Languages

• A core issue underlying the design of
  message-passing based communication is the format
  of the messages.
• Our goal is to support agent interactions that
  exhibit the flexibility that is inherent within
  human conversation.
• As with many agent concepts, we look to
  philosophy in for inspiration
• Speech Act Theory (Searle, 1969) is a pragmatic
  theory of language.
• It attempts to account for how language is used
  by people every day to achieve their goals and
  intentions.
• It achieves this by adopting a view of speech as
  action.

15
Austins Theory

• The origin of speech act theories are usually
  traced to the work of the philosopher John
  Austin.
• Austin noticed that some utterances are like
  physical actions that appear to change the
  state of the world. e.g.
• Declaring war
• I now pronounce you man and wife
• Austin distinguished 3 different aspects of
  speech acts
• Locutionary act - act of making an utterance
• e.g. saying please make some tea
• Illocutionary act action performed in saying
  something
• e.g. he requested me to make some tea
• Perlocution effect of the act
• e.g. he got me to make tea

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Searles Theory

• Searle built on Austins work and identified 5
  types of illocutionary act (which he called
  speech acts)

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Searles Theory

• He then determined that speech acts can be
  decomposed in to 2 core components
• A performative verb
• e.g. Request, inform
• Propositional content
• e.g. the window is closed

18
Modeling Speech Acts

• To understand how speech acts may be applied, we
  need to develop a formal (logical) model.
• At its core, this model must facilitate the
  definition of different speech acts.
• In particular, we need to know when a speech act
  can be applied, and what the effect of that
  speech act will be.
• This is known as semantics.
• Because speech acts are seen as phyiscal actions,
  their semantics can be specified through the use
  of pre- and post- conditions.

19
Example Speech Act

• Semantics for request request(s,h,?)
• Pre
• s believes h can do ? (you dont ask someone to
  do something unless you think that they can do
  it)
• s believes h believes h can do ? (you dont ask
  someone unless they believe they can do it)
• s believes s wants ? (you dont ask someone
  unless you want it!)
• Post
• h believes s believes s wants ? (the effect is
  to make them aware of your desire)

20
Agent Communication Languages

• So, we can model inter-agent communication as
  speech acts.
• In our model, we must specify some model of the
  state of an agent.
• Then we must define a set of speech acts in terms
  of
• the pre-conditions that must be satisfied for the
  act to be performed and
• the expected effects of that speech act
• Finally, we must provide a message format that
  can encode the information that is passed between
  the speaker and the hearer agents.
• The minimum requirement must be the performative
  verb and the propositional content.
• All of this, when put together is known as an
  agent communication language!

21
AOSE

• ACLs KQML

22
Agent Communication Languages

• An Agent Communication Language combines
• a data format for representing speech acts.
• a (partial) model of the state of the speaker an
  hearer.
• a set of formally specified set of speech act
  types (based on the above model).
• As we have seen, at its most primitive, a speech
  act is a combination of a performative verb and
  some propositional content.
• However, humans also use additional contextual
  information in communication such as who
  performed the speech act, and to whom it was
  directed.
• So, in its simplest form, an ACL message might
  look something like this
• request ( rem, bob ) closed(door)

23
Agent Communication Languages

• Other contextual information that is often
  provided in an ACL message include
• The format (knowledge representation language) of
  the propositional content.
• The ontology associated with the propositional
  content.
• The protocol and conversation that the message is
  part of.
• Any encodings (if the content is encrypted)
• However, much of this is optional and is not
  always implemented in real world agent systems.
• The key value of ACLs is that they define a
  clear syntax and semantics for agent
  communication.

24
KQML

• Knowledge Sharing Effort (KSE), funded by ARPA
• Central concept knowledge sharing requires
  communication, which in turn requires a common
  language.
• KSE focused on defining that common language.
• KQML Knowledge Query and Manipulation Language
• Language for both message formatting and message
  handling protocols.
• KIF Knowledge Interchange Format
• Language for expressing message content.

25
KQML and KIF

• KQML is an outer language, that defines various
  acceptable communicative verbs, or
  performatives
• Example performatives
• ask-if (is it true that. . . )
• perform (please perform the following action. .
  . )
• tell (it is true that. . . )
• reply (the answer is . . . )
• KIF is a language for expressing message content

26
KQML Message Structure

• KQML is an outer language, that defines various
  acceptable communicative verbs, or performatives

e.g. (ask-if sender agenti receiver agentj
language Prolog ontology genealogy content (
spouse adam eve))
27
KQML Performative Categories
28
KIF Knowledge Interchange Format

• Used to state
• Properties of things in a domain (e.g., Rem is a
  Lecturer)
• Relationships between things in a domain (e.g.,
  Rem likes beer)
• General properties of a domain (e.g., All
  students are registered for at least one course)

29
KIF Knowledge Interchange Format

• The temperature of m1 is 83 Celsius(
  (temperature m1) (scalar 83 Celsius))
• An object is a bachelor if the object is a man
  and is not married(defrelation bachelor (?x)
  (and (man ?x) (not (married ?x))))
• Any individual with the property of being a
  person also has the property of being a
  mammal(defrelation person (?x) gt (mammal ?x))

30
KQML and KIF

• In order to be able to communicate, agents must
  have agreed on a common set of terms
• A formal specification of a set of terms is known
  as an ontology
• Projects such as the Knowledge Sharing Effort put
  significant effort into defining common
  ontologies.
• This led to the development of software tools
  such as Ontolingua to support this activity.
• Example KQML/KIF dialogueA to B (ask-if (gt
  (size chip1) (size chip2)))B to A (reply
  true)B to A (inform ( (size chip1) 20))B to
  A (inform ( (size chip2) 18))

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KQML Example 1

• (evaluate
• sender A receiver B
• language KIF ontology motors
• reply-with q1 content (val (torque m1)))
• (reply
• sender B receiver A
• language KIF ontology motors
• in-reply-to q1
• content ( (torque m1) (scalar 12 kgf)))

32
KQML Example 2

• (stream-about
• sender A receiver B
• language KIF ontology motors
• reply-with q1 content (m1))
• (tell
• sender B receiver A
• in-reply-to q1
• content ( (torque m1) (scalar 12 kgf)))
• (tell
• sender B receiver A
• in-reply-to q1
• content ( (status m1) (normal)))
• (eos
• sender B receiver A
• in-reply-to q1)

33
KQML Facilitators

• KQML environments (may) contain facilitators that
  help make the communication protocol transparent.
• Facilitators a special class of agents that
  perform useful communication services such as
• Maintain registry of service names
• Forward messages to named services
• Routing messages based on content
• Provide matchmaking between information providers
  and seekers
• Provide mediation and translation services

34
KQML Facilitators
Point-to-point protocol A is aware that it is
appropriate to send a query about X to B There
are several ways to achieve this via a
Facilitator.
F
tell(X)
ask(X)
A
B
35
KQML Facilitators
Using the subscribe performative Request that
Facilitator F monitor for the truth of X. If B
subsequently informs F that it believes X to be
true, then F can in turn inform A.
tell(X)
subscribe(ask(X))
F
tell(X)
A
B
36
KQML Facilitators
advertise(ask(X))
broker(ask(X))
Using the broker performative A Asks Facilitator
to find another agent which can process a given
performative.
tell(X)
F
tell(X)
ask(X)
A
B
37
KQML Facilitators
advertise(ask(X))
recruit(tell(X))
Using the recruit performative Asks Facilitator
to find an appropriate agent to which an embedded
performative can be forwarded. A reply is
returned directly to the original agent.
F
ask(X)
tell(X)
A
B
38
KQML Facilitators
recommend(ask(X))
advertise(ask(X))
Using the recommend performative Asks
Facilitator to respond with the name of another
agent which is appropriate for sending a
particular performative.
reply(B)
F
ask(X)
A
B
tell(X)
39
KQML Criticism

• Weak semantics of performatives
• Different implementations of KQML could not
  interoperate.
• Transportation mechanisms were not defined.
• Lacked the class of performatives commissives
• Difficult to implement multi-agent scenarios
  without commissives.
• Set of performatives is large and ad hoc.

40
AOSE

• FIPA Agent Interaction

41
Who is FIPA?

• The Foundation for Intelligent Physical Agents
  (FIPA) is a non-profit association.
• FIPAs purpose is to promote the success of
  emerging agent-based applications, services and
  equipment.
• FIPA operates through the open international
  collaboration of member organisations
• companies, universities and government
  organisations.
• FIPAs Standards Cover
• Agent Communication (FIPA ACL / Interaction
  Protocols)
• AO-Application Infrastructures (Agent Platform,
  Agent Management, Message Transport Systems)
• Agent UML

42
FIPA ACL 1

• Basic structure is quite similar to KQML
• Performative (communicative act)
• 20 performatives in FIPA ACL
• Housekeeping
• e.g. Sender, Reply to, Reply-with, In-Reply-With
• Content
• the actual content of the message
• Language
• The language in which the content is written
• Ontology
• The ontology in which the message needs to be
  interpreted.

43
FIPA ACL 2 Example Message
ACL message
inform
(
sender

agent1
Note FIPA uses a content language called
FIPA-SL, which is based on modal logic.
receiver


hpl-auction-server
content

(price (bid good02) 150)
in-reply-to

round-4
reply-with

bid04
language


fipa-sl
ontology


hpl-auction
)
44
FIPA ACL 3 - Message Structure
Transport-message HTTP Sender Transport-type
FIPA-HTTP Transport-address http//www.agentfact
ory.com4444/ Transport-properties
none Receiver Transport-type
FIPA-HTTP Transport-address http//www.ibeca.org
4444/ Transport-properties none Additional-attri
butes none
Envelope

• Envelope
• Comprises of a collection of parameters
• Contains at least the mandatory to and sender
  parameters
• Message Body
• The fully specified message in the chosen ACL
  syntax
• Can be encoded (e.g. The FIPA Bit Efficient
  Encoding Mechanism).

Payload (ACL message)
45
FIPA Semantic Language (FIPA-SL)

• FIPA-SL is the formal language used to define the
  semantics of FIPA ACL
• logical propositions are expressed in a logic of
  mental attitudes and actions
• the logical framework is a first order modal
  language with identity (similar to Cohen
  Levesque)
• FIPA-SL provides formalizations for three
  primitive mental attitudes Belief, Uncertainty
  and Choice (or Goal)
• FIPA-SL can express propositions, objects and
  actions.

46
FIPA ACL 4 - Inform and Request

• Inform and Request are the two basic
  performatives in FIPA ACL.
• All others are macro definitions, defined in
  terms of these.
• The meaning of inform and request are defined in
  2 parts
• Precondition
• What must be true in order for the speech act to
  succeed.
• Rational effect
• What the sender of the message hopes to bring
  about.
• FPs and REs involve descriptions of the agents
  state in FIPA-SL.

47
FIPA ACL 5 - Inform and Request
48
FIPA ACL Semantics Inform

• i informs j about ? being true.
• lti, inform( j, ? )gt FP Bi? ? ? Bi( Bifj? ?
  Uifj?) RE Bj?
• The sender
• believes that proposition ? is true
• intends that receiver j also comes to believe
  that ? is true
• does not already believe receiver has any
  knowledge about ? .
• Its up to receiver to adopt the belief.

49
Performatives in FIPA
50
FIPA Transport management

• a platform provides to each agent a channel
• a transfer protocol is used to transfer messages
  between channels
• the transport service delivers messages within a
  platform or between platforms
• ACL is the payload of the transport service and
  protocol
• the envelope contains transport information.

51
FIPA Sending Messages

• 3 options
• Via local ACC
• Via remote ACC
• Direct communication mechanism

52
FIPA Agent Interaction Protocols

• Ongoing conversations between agents fall into
  typical patterns.
• In such cases, certain message sequences are
  expected, and at any point in the conversation,
  other messages are expected to follow.
• These typical patterns of message exchange are
  called protocols.
• (request sender A
• receiver B
• content some-act
• protocol fipa-contract-net
• )

53
Example Query-Protocol

• The protocol states that
• IF an agent asks another agent if a proposition
  holds or not
• THEN the participant must reply with answer
  informing the initiator, or may refuse to answer,
  or fail to answer, or failing to understand the
  question.

54
Comparing KQML and FIPA ACL

• Similarities
• Separation of the outer language (performative)
  and the inner language (content).
• Allows for any content language
• Differences
• Communication primitives
• KQML performative
• FIPA ACL communicative act
• Different semantic frameworks impossible to
  come up with an exact mapping or transformation
  between KQML and FIPA performatives.
• KQML provides facilitator services FIPA ACL
  originally did not.