Knowledgebased systems Tutorial

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Knowledge-based systemsTutorial

• Introduction to G2
• Rozália Lakner
• University of Veszprém
• Department of Computer Science

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Contents

• Main characteristics of G2
• Main components of G2 knowledge base
• Reasoning in G2
• Development of knowledge base

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Main characteristics of G2
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G2 a real-time expert system

• used for rapid prototyping and implementing
  expert systems
• G2 possess features and properties of an expert
  system shell
• user-friendly interfaces
• well-structured natural language in a high-level
• graphic-oriented environment
• inference engine (and simulator)
• forward and backward reasoning
• elements of knowledge base (items)
• objects, workspaces, connections, relations,
  variables, parameters, rules, procedures,
  functions
• tools for developing knowledge base

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Main components of G2 knowledge base
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Objects

• representation of some part of the application
• water-tank, valve, coffee-machine
• picture of each object icon
• generated manually (permanent objects)
• has a table of attributes (contains the knowledge
  about the object)
• object classes
• attributes, icon are inherited
• own specific attributes
• object hierarchy
• actual application objects instances

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Variables, parameters

• built-in object classes
• represent things that have changing values
• temperature, level,
• similarities
• attributes, classes, icon, history keeping
• differences
• a value of a variable may expire
• a parameter always has current value (initial
  value)
• a variable has validity interval
• data-seeking sources for variable value
• internal data server
• inference engine (backward changing)
• G2 simulator

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Workspaces

• rectangular areas
• can contain items (objects, connections, rules,
  )
• workspace-hierarchy
• enabling/disabling workspaces
• permanent/temporary workspaces

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Connections, relations

• connection
• relationship between objects (created manually)
• graphically links two objects together
  (flow-pipe, electrical wire)
• represents abstract relationship (partnership,
  ownership)
• classes of connections
• objects can be referred based on connection
• possible to write generic rules (any tank
  connected to any valve)
• relation
• relationship between objects (created
  dynamically, conclude action)
• classes of relations
• has not graphical representation
• doesnt saved as part of a knowledge base

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Rule types 1

• If rules (common rules)
• for any valve V
• if the state of V 1
• then change the center stripe-color of every
  flow-pipe
• connected to V to sky-blue
• When rules (cannot be used in reasoning)
• for any container-or-vessel CV
• when the value of the inventory of CV 0
• then conclude that the temperature of CV has no
  value
• Initial rules (invoked when KB starts or
  restarts)
• initially for any container-or-vessel CV
• if the inventory of CV gt 0
• then conclude that the temperature of CV 15

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Rule types 2

• Unconditional rules (rules without condition
  part)
• initially for any valve V
• unconditionally conclude that the state of V 0
• Whenever rules (event-controlled rules)
• whenever auto-manual-state receives a value and
• when the value of auto-manual-state is auto
• then start auto()

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Main attributes of rules

• options (how can use the rule)
• scan interval (how often to invoke the rule)
• rule priority (in case of overloading)
• depth-first backward chaining precedence
  (conflict resolution)
• timeout for rule completion (how long G2 may try
  to evaluate the condition part)

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Procedures

• sequence of operations executed by G2
• like high-level procedural languages
• main part of procedures
• procedure header (name, typed argument list,
  return type)
• local declarations
• procedure body (begin, sequence of procedure
  statements, end)

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Reasoning in G2
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Real-time inference engine 1

• functions of inference engine (IE)
• reasons about the current state of the
  application
• communicates with the end-user
• iniciates other activity based upon what it has
  inferred
• IE operates on the following sources of
  information
• the knowledge contained in the knowledge base
• simulated values
• values received from sensors and other external
  sources

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Real-time inference engine 2

• abilities of IE
• scan rules repeatedly invoke a rule at regular
  time interval (scan interval)
• wakeup rules when a variable receives a value,
  the inference engine wakes up the rule that was
  waiting for the value of the variable
• data seeking get value from the specified data
  server (when the value of the variable is
  expired)
• chaining the rules (reasoning)
• backward chaining IE infers the value of a
  variable with the help of rules (when the value
  of a variable is not given by a sensor or a
  formula)
• forward chaining IE invoke a rule when its
  condition part is satisfied by another rule

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G2 simulator

• special data server in G2

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Development of knowledge-base
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Developer interface 1

• graphic-oriented environment
• creating the model of the application graphically
  (schematic)
• objects are represented by icons
• objects are placed in workspaces
• objects are connected graphically
• pop-up menus for objects (attribute table,
  delete, change size and colour, move, )

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Developer interface 2

• well-structured natural language in a high-level
• referring to an item
• by name coffee-machine
• by class name the vessel
• as an instance of a class is nearest to another
  item on schematic the level-icon nearest to
  coffee-machine
• as an instance of a class that is connected to an
  object by an input or output connection the
  valve connected at the output of coffee-machine

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Developer interface 3

• interactive text editor
• text-edit workspace
• inserting text from other items or scrapbook
• syntax-checking
• marking incorrect text
• warning message
• suggestion for correction

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Developer interface 4

• interactive icon editor
• graphic tool
• design icons graphically
• converting into G2 grammar
• layers, regions
• main parts of icon editor
• icon view
• buttons for creating graphic elements
• icon size display
• cursor location display
• layer pad and layer display

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Developer interface 5

• tools for managing large KBs
• clone objects and statements
• operate on a group of objects
• inspect utility (browse KB) finding items easy
• describe facility (informations about item)
  data server, rules
• organize knowledge hierarchically (workspaces,
  subworkspaces, activate/ deactivate)
• merge KBs

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Developer interface 6

• documentation in KB free texts (only for
  documentation, is not part of KB)
• tracing and debugging facilities
• warning messages (errors, unusual conditions)
• trace messages
• current value of variable, expression (each time
  it receives one)
• starting and finishing time of evaluating of
  variable, formula, rule, procedure, function
• set breakpoints
• highlight invoked rules
• access control facilities
• restrict the choices a user has on the menus
• restrict moving items, making connections,
• restrict accessing to the attribute table
• restrict editing of attributes
• mode of operation (specify restrictions)
  operator, administrator, developer,

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User interface 1

• displays
• screen items showing the value of variable,
  parameter, expression
• end-user controls
• control an application by the user
• messages, message board
• items that display text
• are used for communication

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User interface 2

• displays
• readout table
• variable, parameter and its value
• chart
• plots of one or more variables
• history of values change over time
• meter
• value of variable in a vertical display
• dial
• value of variable in a round scale
• freeform table
• tabular form of variables values

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User interface 3

• end-user controls
• action buttons
• execute an action (start, conclude, show, )
• radio buttons
• assign a predefined value for variable or
  parameter
• check box
• assign on or off value for variable or
  parameter
• slider
• enter numeric value for variable or parameter by
  sliding a pointer
• type-in box
• enter a value for variable or parameter from
  keyboard