ARTIFICIAL INTELLIGENCE [INTELLIGENT AGENTS PARADIGM]

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ARTIFICIAL INTELLIGENCEINTELLIGENT AGENTS
PARADIGM
KNOWLEDGEREPRESENTATION SCHEMAS

• Professor Janis Grundspenkis
• Riga Technical University
• Faculty of Computer Science and Information
  Technology
• Institute of Applied Computer Systems
• Department of Systems Theory and Design
• E-mail Janis.Grundspenkis_at_rtu.lv

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Knowledge Representation Schemas

• Logical schemas
• First-order logic
• Higher-order logic
• Procedural schemas
• Rule-based systems

• Network schemas
• Semantic networks
• Conceptual graphs
• Structured schemas
• Frames
• Scripts

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Semantic Networks

• Definition Semantic network (Quillian, 1967) is
  a knowledge representation schema that captures
  knowledge as a graph. The nodes denote objects or
  concepts, their properties and corresponding
  values. The arcs denote relationships between the
  nodes. Both nodes and arcs are generally labelled
  (arcs have weights).

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Example of Semantic Network
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Semantic Networks

• Typical relationships
• IS-A
• PART-OF
• HAS
• VALUE
• LINGUISTIC

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Semantic Networks

• Typical relationships (continued)
• IS-A
• Supertype type (superclass class)
• Type subtype (class subclass)
• Subtype instance (subclass instance)
• PART-OF
• Supertype type (superclass class)
• Type subtype (class subclass)

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Semantic Networks

• Typical relationships (continued)
• HAS
• Object property
• VALUE
• Property value
• LINGUISTIC
• Examples likes, owns, travel, made of,

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Semantic Networks

• NETWORK EXTENSION
• Addition of new nodes and their relationships
• Three ways of node addition
• Similar object
• More specific object
• More general object

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Semantic Networks

• REASONING
• Query node
• Answer search
• Answer localization at the query node
• Path construction following labels of arcs

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Semantic Networks

• INHERITANCE
• Definition Inheritance is a process by which the
  local information of a superclass node is assumed
  by a class node, a subclass node, and an instance
  node

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Semantic Networks

• INHERITANCE (continued)
• 1) Provides a natural tool for representing
  taxonomically structured knowledge. 2) Provides
  economical means of expressing properties common
  to a class of objects. 3) Reduces the size of a
  knowledge base. 4) Provides more compact code
• 1) Exception handling by local priority. 2)
  Additional workload of knowledge engineer who
  must decide at which node to define common
  properties

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Conceptual Graphs

• DEFINITION A conceptual graph (John Sowa, 1984)
  is a finite, connected, bipartite graph
• The nodes of the graph denote either concepts or
  conceptual relations
• Conceptual graphs do not use labelled arcs
  instead the conceptual relation nodes represent
  relations between concepts
• Concepts can only have arcs to conceptual
  relations, and vice versa
• Concepts are represented as boxes and conceptual
  relations as ellipses

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Conceptual Graphs

• Concept nodes represent
• Concrete concepts (objects), for instance, cat,
  telephone, book , etc. These concepts are
  characterised by our ability to form an image of
  them in our minds. Concrete concepts include
  generic concepts such as cat or book along with
  concepts of specific cats and books
• Abstract concepts, for instance, beauty, loyalty,
  and love that do not correspond to images in our
  minds

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Conceptual Graphs

• Conceptual relation nodes indicate a relation
  involving one or more concepts. Some special
  relation nodes, namely, agent, recipient, object,
  experiencer, are used to link a subject and the
  verb
• Conceptual graphs can represent relations of any
  arity
• A relation of arity n is represented by a
  conceptual relation node having n arcs

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Example of Conceptual Graph
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Conceptual Graphs

• Each conceptual graph represents a single
  proposition
• Knowledge base contains a set of conceptual
  graphs
• Graphs may be arbitrary complex but must be
  finite

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Frame Based Systems

• The term frame is coined by Minsky in 1975.
• Frame is a static data structure used to
  represent stereotypical information about some
  concept.
• Frame is like a template that contains generic
  information about some concept that you could
  refer to for describing a given instance of the
  concept.

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Frame Based Systems

• A frame has
• Name frame identification information.
• Slots with labels describing the attributes and
  possible values for each attribute.

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Frame Based Systems

• The slots contain
• Frame identification information
• Relationship of this frame to other frames
• Frame default information (slot values that are
  taken to be true when no evidence to the contrary
  has been found)
• New instance information (slots may be left
  unspecified)
• Procedural information (procedural code may be
  attached to the slot)
• Descriptors of requirements for frame match

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Frame Based Systems

• ATTRIBUTES
• STATIC
• DYNAMIC
• VALUES
• NUMERIC
• SYMBOLIC
• BOOLEAN

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Frame Based Systems

• Sources of attribute values
• Initialize
• Database
• Procedure
• Expert System
• User
• Inheritance
• Other Frame (object)

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Frame Based Systems

• CLASS
• Definition Class is a collection of objects that
  share some common properties (attributes).
• A class frame contains
• A descriptive name of the concept
• A set of attributes that are characteristic of
  all its associated objects
• Attribute values that considered common to these
  objects
• It may contain 1) An explicit reference to all
  of its associated subclasses 2) Information
  describing the behaviour of the concept.

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Frame Based Systems

• SUBCLASSES
• Definition Subclasses are classes that represent
  subsets of higher level classes.
• Three kinds of class relationships
• Generalization Kind of relationship
• Aggregation Part of relationship
• Association Semantic relationship

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Frame Based Systems

• INSTANCE
• Definition Instance is a specific object from a
  class of objects.
• AN INSTANCE FRAME
• Describes
• A specific object from its related class.
• Contains
• All of the characteristics of the class frame as
  well as a specific information (specific features
  and property values).

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Example of Frame Based System
truck truck
class vehicle class vehicle
reg. number
producer
model
owner
tonnage
part of basket
superclass vehicle superclass vehicle
reg. number
producer
model
owner
basket basket
dimensions 231.5
material tin
car car
class vehicle class vehicle
reg. number
producer
model
owner
number of doors 4
horse-power
Johns car Johns car
class car class car
reg. number LV97
producer BMW
model 520
owner John
number of doors 2
horse-power 150
John John
age 22
length of driving 2
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Frame Based Systems

• INHERITANCE
• Definition Inheritance is the process by which
  the characteristics of a parent frame are assumed
  by its child frame.
• Note In general, a child frame will inherit
  information from its parents, grandparents,
  great-grandparents, etc.
• MULTIPLE INHERITANCE
• An object could inherit information from more
  than one parent (in this case objects relate to
  different worlds)

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Frame Based Systems

• INHERITANCE
• Practical value
• Easier coding of the system
• Easier modification of information in a frame
  (adding new property to the class frame it will
  be inherited automatically by all of its
  instances)
• Potential problem exception handling
• Any frame that is an exception from the norm,
  that is, the frame has some property value unique
  to itself, this value must be explicitly encoded
  in the frame.

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Frame Based Systems

• FACETS
• Definition A facet is an extended knowledge
  about a frames property.
• Facets provide additional control over property
  value and the operation of the system.

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Frame Based Systems

• A facet extends the information in the following
  ways
• TYPE Defines a type of value that can be
  associated with the property
• DEFAULT Defines a default value, i.e., an
  initial value for the property
• CONSTRAINT Defines the allowable value

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Frame Based Systems

• MINIMUM CARDINALITY Establishes min number of
  values
• MAXIMUM CARDINALITY Establishes max number of
  values
• IF-NEEDED Specifies action to be taken if the
  propertys value is needed
• IF-CHANGED Specifies action to be taken if the
  propertys value is changed

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Frame Based Systems

• METHODS (1)
• Definition Method is a procedure attached to an
  object, that will be executed whenever requested.
• An IF-NEEDED method is written in order to obtain
  the propertys value only when it is needed.
  IF-NEEDED facet executes some method only when it
  is needed (method acts like a demon).

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Frame Based Systems

• METHODS (2)
• An IF-CHANGED method is written in order to
  change an objects property value, access
  database, etc. IF-CHANGED facet executes some
  method that performs some function in the event
  the property's value changes.
• Methods designed to perform both operations can
  be inherited.

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Example of Methods
Temperature sensors
Name
Unknown
Value
Unknown
Value If-Needed Method
Value If-Changed Method
Unknown
Critical Value
Get-Value (Self.Name)
IF Self.Value gt Self.Critical Value THEN
Self.Status Alert
Status If-Changed Method
Status
Unknown
IF Self.Status Alert THEN Sound-Alert
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Frame Based Systems

• COMMUNICATION BETWEENOBJECTS (1)
• Interobject communication using facets
• Using facet methods objects can communicate with
  one another. A change to only one property value
  may cause a series of changes in a number of
  objects (frame system is dynamic!). Objects can
  influence the property values in other objects,
  or even itself.

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Frame Based Systems

• COMMUNICATION BETWEENOBJECTS (2)
• Message passing
• Definition Message passing is a signal to an
  object to which the object responds by executing
  a method.
• Sending messages involves using a function
• (SEND message-name, object-name, arguments)