LECTURE 7: Agent Communication

1
LECTURE 7 Agent Communication

• Based on
• An Introduction to MultiAgent Systemshttp//www.c
  sc.liv.ac.uk/mjw/pubs/imas
• Presentation by Nyik San Ting, spring 2003.

2
Agent Communication

• In this lecture and the next, we cover
  macro-aspects of intelligent agent technology
  those issues relating to the agent society,
  rather than the individual
• communicationspeech acts KQML KIF FIPA ACL
• cooperationwhat is cooperation prisoners
  dilemma cooperative versus non-cooperative
  encounters the contract net

3
Contents

• Tuesday (12 Oct 2004)
• Speech Acts
• KQML, KIF
• FIPA ACL
• Ontology

• Thursday (14 Oct 2004)
• Ontology development
• KIF
• XML RDF
• DAML

4
Speech Acts

• Most treatments of communication in (multi-)
  agent systems borrow their inspiration from
  speech act theory
• Speech act theories are pragmatic theories of
  language, i.e., theories of language use they
  attempt to account for how language is used by
  people every day to achieve their goals and
  intentions
• The origin of speech act theories are usually
  traced to Austins 1962 book, How to Do Things
  with Words

5
Speech Acts - Austin

• Communication action
• Doesnt mean
• Motion of moving mouth
• Changing the pressure of the air by talking.
• Causing the avalanche by shouting.
• The semantic meaning (effect) of the utterance
• Lets send a bomb to Iraq.

6
Speech Acts

• Austin noticed that some utterances are rather
  like physical actions that appear to change the
  state of the world
• Paradigm examples would be
• declaring war
• christening
• I now pronounce you man and wife -)
• But more generally, everything we utter is
  uttered with the intention of satisfying some
  goal or intention
• A theory of how utterances are used to achieve
  intentions is a speech act theory

7
Speech Acts - Austin

• Communication action
• Doesnt mean
• Motion of moving mouth
• Changing the pressure of the air by talking.
• Causing the avalanche by shouting.
• The semantic meaning (effect) of the utterance
• Lets send a bomb to Iraq.

8
Elements
9
Speech Acts - Austin

• 3 aspects of Speech Acts
• Locutionary act
• Illocutionary act
• Perlocution

10
Different Aspects of Speech Acts

• From A Dictionary of Philosophical Terms and
  Names
• Locutionary act the simple speech act of
  generating sounds that are linked together by
  grammatical conventions so as to say something
  meaningful. Among speakers of English, for
  example, It is raining performs the locutionary
  act of saying that it is raining, as Grablistrod
  zetagflx dapu would not.
• Saying something that make sense using a language
• Saying Please make some tea
• Saying Tuition fee will increase by 50 next
  year

11
Different Aspects of Speech Acts

• Illocutionary act the speech act of doing
  something else offering advice or taking a vow,
  for example in the process of uttering
  meaningful language. Thus, for example, in saying
  I will repay you this money next week, one
  typically performs the illocutionary act of
  making a promise.
• Action intended by the speaker
• He requested me to make some tea
• The Dean of the University announced that the
  tuition fee will increase by 50 next year

12
Different Aspects of Speech Acts

• Perlocutionary act the speech act of having an
  effect on those who hear a meaningful utterance.
  By telling a ghost story late at night, for
  example, one may accomplish the cruel
  perlocutionary act of frightening a child.
• Effect of the action
• He got me to make tea
• Everyone is informed and understand that the
  tuition fee will increase by 50 next year

13
Shoot her!

• Locutionary act of saying Shoot her!
• Illocutionary force of ordering, urging, or
  advising the hearer to shoot her
• Perlocutionary force of persuading,
  forcing,frightening the hearer to shoot her
• Example obtained from 2

14
Performative Utterance

• I warn you that they raise the gas price
  dramatically
• First verb in the sentence
• They raise the gas price dramatically
• Felicitous performative
• Performative utterance that works successfully

15
Felicity conditions

1. An accepted conventional procedure for the
   performative the circumstances and persons must
   be as specified.
2. Procedure must be executed correctly and
   completely
3. Act must be sincere uptake required must be
   completed as much as possible.

16
Speech Acts

• John Searle extended the work of John Austin in
  1969
• Identified properties that must hold for a speech
  act performed between hearer and the speaker to
  succeed.
• Systematic classification of the possible types
  of speech acts

17
Speech Acts Conditions for a speech act to
succeed

• Normal I/O conditions
• HEARER can hear the utterance
• Preparatory conditions
• What must be true of the world in order that
  SPEAKER correctly choose the speech act
• Sincerity conditions
• Distinguish the sincerity of the performance of
  the speech act

18
Speech Acts

• Searle (1969) identified various different types
  of speech act
• representatives Commits the speaker to the
  truth of an expressed proposition, such as
  informing, e.g., It is raining
• directives Attempts on the part of the speaker
  to get the hearer to do something e.g., please
  make the tea
• commisives Commit the speaker to doing
  something, e.g., I promise to
• expressives Speaker expresses a mental state,
  e.g., thank you!
• declarations Effect some changes in an
  institutional state of affairs, such as
  declaring war or christening

19
Speech Acts

• There is some debate about whether this (or any!)
  typology of speech acts is appropriate
• In general, a speech act can be seen to have two
  components
• a performative verb(e.g., request, inform,
  promise, )
• propositional content(e.g., the door is
  closed)

20
Speech Acts

• Consider
• performative requestcontent the door is
  closedspeech act please close the door
• performative informcontent the door is
  closedspeech act the door is closed!
• performative inquirecontent the door is
  closedspeech act is the door closed?

21
Plan Based Semantics

• How does one define the semantics of speech acts?
  When can one say someone has uttered, e.g., a
  request or an inform?
• Cohen Perrault (1979) defined semantics of
  speech acts using the STRIPS formalism for
  planning precondition-delete-add list
• The world is a multimodal logic representation
  for the Beliefs, Abilities, Wants of the
  participants in the speech act
• Note that a speaker cannot (generally) force a
  hearer to accept some desired mental state
• In other words, there is a separation between the
  illocutionary act and the perlocutionary act

22
Plan-Based Semantics

• Here is their semantics for requestrequest(s,
  h, f)
• pre
• s believe h can do f(you dont ask someone to do
  something unless you think they can do it)
• s believe h believe h can do f(you dont ask
  someone unless they believe they can do it)
• s believe s want f(you dont ask someone unless
  you want it!)
• post
• h believe s believe s want f(the effect is to
  make them aware of your desire)

Note that request ensures only that h is aware of
s desire locution only!!
23
Mediating act
In order to ensure that there is perlocutionary
force need a mediating act

• CauseToWant(A1, A2, ?)
• Preconditions
• Cando.pr
• (A1 BELIEVE (A2 BELIEVE (A2 WANT ?)))
• Want.pr
• X
• Effect
• (A1 BELIEVE (A1 WANT ?))

By this definition, the agent will come to
believe that it wants something, if it
believesthat another agent believes it wants to
do it. This definition can be extended to
contain more conditions related to social
relationships, role etc.
24
KQML and KIF

• We now consider agent communication languages
  (ACLs) standard formats for the exchange of
  messages
• The best known ACL is KQML, developed by the ARPA
  knowledge sharing initiativeKQML is comprised of
  two parts
• the knowledge query and manipulation language
  (KQML)
• the knowledge interchange format (KIF)

25
KQML and KIF

• KQML is an outer language, that defines an
  envelope format for messages to explicitly
  state the intended illocutionary force
• KQML defines various acceptable communicative
  verbs, or performativesExamples
• 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
  (ONTOLOGIES later)

26
Example

• (tell
• content ( (temperatute m1) (scalar 83
  Celsius))
• sender termometer-server
• receiver heater
• language KIF
• ontology ONTOLOGY_NAME
• )

Inform another agent about some fact. Formal
definition S claims to R that C is in Ss VKB.
27
Another example
There are variants ask-if, ask-all, ask-about

• (ask-one
• content (PRICE ISM ?price)
• receiver stock-server
• language LPROLOG
• ontology NYSE-TICKS
• )

Ask another agent a question where exactly one
answer is required. Formal S wants one of Rs
answers to question C
28
FIPA

• More recently, the Foundation for Intelligent
  Physical Agents (FIPA) started work on a program
  of agent standards the centerpiece is an ACL
• Basic structure is quite similar to KQML
• performative20 performatives in FIPA
• housekeepinge.g., sender, etc.
• contentthe actual content of the message

29
FIPA

• Example(inform sender agent1 receiver agent
  5 content (price good200 150) language sl on
  tology hpl-auction)

30
FIPA
31
FIPA ACL Semantics

• Semantics of ACL preformatives are given with
  respect to a formal SL (Semantic Language)
• Represent beliefs, desires, uncertain beliefs of
  agents and actions that agents perform
• Well defined, in contrast to KQML
• Each FIPA ACL message can be mapped to a formula
  of SL
• Defines a constraint that the sender must satisfy
• (Feasibility conditions)
• Defines the rational effect of the action - the
  purpose of a message (cannot be guaranteed)

32
Inform and Request

• Inform and Request are the two basic
  performatives in FIPA. All others are macro
  definitions, defined in terms of these.
• The meaning of inform and request is defined in
  two parts
• pre-conditionwhat must be true in order for the
  speech act to succeed
• rational effectwhat the sender of the message
  hopes to bring about

33
Inform and Request

• For the inform performativeThe content is a
  statement.Pre-condition is that sender
• holds that the content is true
• intends that the recipient believe the content
• does not already believe that the recipient is
  aware of whether content is true or not

34
Inform and Request

• For the request performativeThe content is an
  action.Pre-condition is that sender
• intends action content to be performed
• believes recipient is capable of performing this
  action
• does not believe that receiver already intends to
  perform action

35
Semantic Conformance Testing

• Woolridge
• ACL semantics are generally developed in such a
  way as to express constraint on the sender of the
  message
• Specification
• Problem
• Need to know the mental state of agents (what
  they believed, intended and so on)

36
Figure obtained from 5
37
References on Agent Communication Languages

• Austins Speech Act Theory by Saeed
• http//www.ohiou.edu/dlcds/saaustin.htm
• Speech Acts
• http//www.ccl.umist.ac.uk/teaching/material/5005/
  node24.html
• Cohen and Levesque - intention
• http//www.csc.liv.ac.uk/mjw/pubs/ker95/subsubsec
  tionstar3_2_6_2.html
• 4 . FIPA ACL Message Structure Specification by
  FIPA
• http//www.fipa.org/specs/fipa00061/SC00061G.html
• 5. FIPA Communicative Act Library Specification"
  by FIPA
• http//www.fipa.org/specs/fipa00037/SC00037J.html

38
Ontologies

• Different understanding of the terminology

39
Knowledge Sharing among AgentsKQML 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
• The knowledge sharing effort has associated with
  it a large effort at defining common ontologies
  software tools like Ontolingua for this purpose
• 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))

40
Why we need ontology?

• To share common understanding of the structure of
  information among people or software agents
• To enable reuse of domain knowledge
• To make domain assumptions explicit
• To separate domain knowledge from the operational
  knowledge
• To analyze domain knowledge

41
Ontology

• A systematic account of Existence in Philosophy
• Explicit formal definition of the terminologies
  describing the concepts or objects (and their
  attributes) of a domain and the relations among
  them.
• A specification of vocabulary/definition (human
  readable machine interpretable) and their
  relations that model the real world

42
KIF Knowledge Interchange Format

• Based-on first order logic recast in a LISP (LISt
  Processing)-like notation.
• Used to state
• Properties of things in a domain (e.g., Noam is
  chairman)
• Relationships between things in a domain (e.g.,
  Amnon is Yaels boss)
• General properties of a domain (e.g., All
  students are registered for at least one course,
  Everybody has a mother)

43
KIF (2)

• 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))

44
KIF (3)

• Usual connectives
• and, or, not,
• Universal and existential quantifiers
• forall, exist
• Set Relation
• Subset, /, , Member, Disjoint
• Object type
• Numbers (1,2,3 ) characters, strings
• Object relation
• Cos, Max, Log, lt,

45
KIF (4)

• Define new class
• New class of primary-color which take value of
  red, green, or blue
• (define-class primary-color (?color) (member
  ?color (set red green blue)))

46
KIF (5)

• Define new concept
• New concept of bachelor which is a man and this
  man is not married
• (defrelation bachelor (?x)
• (and (man ?x) (not (married ?x))))

47
KIF (6)

• Define new relationships
• Any individual with the property of being a
  person also has the property of being a mammal
• (defrelation person (?x) gt (mammal ?x))
• Note A mammal might not be a person!

48
Extensible Markup Language -XML

• XML is
• a method for embedding structure and meaning in
  data files.
• a new technology for managing data, particularly
  suitable for web applications.
• is text (humans and machines readable)

49
Example

• Dr. John Cooke
• 57 Campus Drive,
• Saskatoon, SK S7N5A9

50
Representation in HTML

• ltPgtltBgtDr. Julita Vassilevalt/Bgt
• ltBRgt110 Science Place,
• ltBRgtSaskatoon, SK S7N 5C9lt/Pgt
• HTML tags describe how something should render.
• They don't contain any information about what the
• data is, they only describe how it should look.
• The set of HTML tags is fixed as defined by the
  DTD (Document Type Definition).

51
Representation in XML

• ltaddressgt
• ltnamegt
• lttitlegtDr. lt/titlegt
• ltfirst_namegtJulitalt/first_namegt
• ltlast_namegtVassilevalt/last_namegt
• lt/namegt
• ltstreetgt110 Science Placelt/streetgt
• ltcitygtSaskatoonlt/citygt
• ltprovincegtSKlt/provincegt
• ltpcodegtS7N 5C9lt/pcodegt
• lt/addressgt

Note semantic tags! Using XML it is possible to
define new tags by writing an XML DTD.
52
Resource Description Framework

• RDF is
• is a model for describing resources, mainly
  internet resources
• A way for publishing human readable and machine
  processable vocabularies

53
Example
Figures obtained from 10
54
Example (2)
lt?xmlnamespace ns "http//www.w3.org/RDF/RDF/"
prefix "RDF" ?gt lt?xmlnamespace ns
"http//purl.oclc.org/DC/" prefix "DC" ?gt
ltRDFRDFgt ltRDFDescription RDFHREF
"http//uri-of-Document-1"gt ltDCCreatorgtJohn
Smithlt/DCCreatorgt lt/RDFDescriptiongt
lt/RDFRDFgt
55
DAML

• DARPA Agent Markup Language
• Based on XML, integration with Ontologies ? The
  Semantic Web
• DAML 0.5, August 2000
• DAML-ONT, October 2000
• DAMLOIL (Ontology Interface Layer), December
  2000

56
DAMLOIL

• A semantic markup language for Web resources
• Uses XML and RDF
• Provides a higher level of information than XML

57
Define Class

• ltdamlClass rdfID"Animal"gt
• ltrdfslabelgtAnimallt/rdfslabelgt
• ltrdfscommentgt
• This class of animals is illustrative of a
  number of ontological idioms.
• lt/rdfscommentgt
• lt/damlClassgt

58
Define Subclass

• ltdamlClass rdfID"Male"gt
• ltrdfssubClassOf rdfresource"Animal"/gt
• lt/damlClassgt
• ltdamlClass rdfID"Female"gt
• ltrdfssubClassOf rdfresource"Animal"/gt
• ltdamldisjointWith rdfresource"Male"/gt
• lt/damlClassgt

59
Defining Property Restriction

• ltdamlClass rdfabout"Animal"gt
• ltrdfscommentgt
• Animals have exactly two parents, ie
• If x is an animal, then it has exactly 2
  parents
• (but it is NOT the case that anything that
  has 2 parents is an animal).
• lt/rdfscommentgt
• ltrdfssubClassOfgt
• ltdamlRestriction damlcardinality"2"gt
• ltdamlonProperty rdfresource"hasParent"/gt
  
• lt/damlRestrictiongt
• lt/rdfssubClassOfgt
• lt/damlClassgt

60
Define Properties

• ltdamlObjectProperty rdfID"hasParent"gt
• ltrdfsdomain rdfresource"Animal"/gt
• ltrdfsrange rdfresource"Animal"/gt
• lt/damlObjectPropertygt
• ltdamlObjectProperty rdfID"hasFather"gt
• ltrdfssubPropertyOf rdfresource"hasParent"/gt
• ltrdfsrange rdfresource"Male"/gt
• lt/damlObjectPropertygt

61
Ontology of Ontology

• Classes or Concepts
• description of concepts in the domain of
  discourse
• Subclasses
• Represent concepts that are more specific
• Slots / Role / Properties
• Properties of concept (various features and
  attributes)
• Facets or role restrictions
• Restriction on slots (value type, allowed value,
  cardinality )

Ontology Instances of Classes Knowledge Base
62
Ontology Examples
People
Position
Age
Sex
63
Ontology Examples (2)
from Noy McGuinness, black for classes, red for
instances, direct links represent slots and
internal links such as instance-of and
subclass-of.
64
Fundamental Rules in Ontology Design

• No correct way to model a domain
• There are viable alternatives
• Best solution depends on application and
  extensions
• Iterative process
• Concepts should be close to (physical or logical)
  objects and relationships in the domain of
  interest.
• Nouns (objects) or verbs (relationships)

65
Ontology Development Steps

• Determine the domain and scope of the ontology
• Consider reusing existing ontologies
• Enumerate important terms in the ontology
• Define the classes and the class hierarchy
• Top-down
• Bottom-up
• Combination

66
Ontology Development Steps (2)

• 5. Define the properties of classes - slots
• Define the facets of the slots
• Slot cardinality
• Slot-value type (String, Number, Boolean,
  Enumerated, Instance-type)
• Domain and range of a slot

67
Ontology Development Steps (3)
from Noy McGuinness, the definition of a slot
Produces that describes the wines produced by
Winery.
68
Ontology Development Steps (4)

• 7. Create instances

Figure from Noy McGuinness - the definition of
an instance of the Beaujolais class
69
Things to lookout

• A subclass of a class represents a concept that
  is a kind-of the concept that the superclass
  represents
• Classes represent concepts in the domain and NOT
  the words that denote these concepts (prawn
  shrimp)
• Avoid class cycles
• How many is too many and how few are too few?

70
Things to lookout (2)

• When to introduce a new class (or not)?
• Usually it should
• Have additional properties (new slots)
• Have different restrictions (different facets)
• Participate in different relationships than the
  super-classes (new slot value defined)
• Can just be a hierarchy of terms

71
Things to lookout (3)

• A new class or a property value?
• If the concepts with different slot values become
  restrictions for different slots in other classes
  -gt create new class
• An instance or a class?
• Natural hierarchy?
• Most specific concepts?
• Limiting the scope
• Naming convention and consistency

72
Languages for Ontologies

• First order logic-based
• KIF-based Ontololingua,
• Loom,
• Frame-Logic
• XML based
• SHOE,
• Ontology Exchange Language (XOL),
• Ontology Markup Language (OML and CKML),
• RDF based
• Resource Description Framework Schema Language
  (RDFS)
• OIL (Ontology Interchange Language)
• DAMLOIL
• OWL

73
OWL Web Ontology Language for the Semantic Web
(W3C)

• XML provides a surface syntax for structured
  documents, but imposes no semantic constraints on
  the meaning of these documents.
• XML Schema is a language for restricting the
  structure of XML documents and also extends XML
  with datatypes.
• RDF is a datamodel for objects ("resources") and
  relations between them, provides a simple
  semantics for this datamodel, and these
  datamodels can be represented in an XML syntax.
• RDF Schema is a vocabulary for describing
  properties and classes of RDF resources, with a
  semantics for generalization-hierarchies of such
  properties and classes.
• OWL adds more vocabulary for describing
  properties and classes among others, relations
  between classes (e.g. disjointness), cardinality
  (e.g. "exactly one"), equality, richer typing of
  properties, characteristics of properties (e.g.
  symmetry), and enumerated classes.

74

XML DTD XML Schema RDF(S) DAMLOIL RDF(S) 2002 OWL
bounded lists X X X
cardinality constraints X X X X
class expressions X X
data types X X ? X
defined classes X X
enumerations X X X X
equivalence X X
extensibility X X X X
formal semantics X X X
inheritance X X X X
inference X X
local restrictions X X
qualified constraints X
reification X X X X
From http//www.daml.org/language/features.html
Discussion
75
Tools for ontology development

• Protégé-2000
• http//protege.stanford.edu/
• Ontolingua
• http//www.ksl.stanford.edu/software/ontolingua/
• DAG-Edit
• http//www.godatabase.org/dev/editor.html
• OilEd
• http//oiled.man.ac.uk/
• Reggie Metadata Editor
• http//metadata.net/dstc/

76
Summary on Ontology development

• No one correct way for developing ontologies
• No one correct ontology for any domain
• Issues
• Rapid domain evolution
• Variety of ontologies in a domain
• Ontology representation
• Efforts for ontology interoperability (ontology
  mapping)
• Stanford Scalable Knowledge Composition (SKC)
  project and the Bremer Semantic Translation
  project

77
References on Ontologies

• Descriptive and Formal Ontology by Raul
  Corazzon. http//www.formalontology.it/
• What is an Ontology? by Tom Gruber
• http//www-ksl.stanford.edu/kst/what-is-an-ontolo
  gy.html
• Ontology Development 101A Guide to Creating
  Your First Ontology by Natalya F. Noy and
  Deboral L. McGuinness
• http//protege.stanford.edu/publications/ontology_
  development/ontology101-noy-mcguinness.html

78
References (2)

• 4. Knowledge Interchange Format (KIF)
• http//www-ksl.stanford.edu/knowledge-sharing/kif
• 5. Knowledge Interchange Format Specification
• http//logic.stanford.edu/kif/specification.html
• 6. DAML homepage.
• http//www.daml.org/
• 7. An Introduction to the Resource Description
  Framework
• http//www.dlib.org/dlib/may98/miller/05miller.htm
  l