Lecture 3 - Supplement

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Lecture 3 - Supplement

• TMS Functioning
• Content
• Types of nodes
• Data structures for a TMS
• TMS/IE responsibilities
• TMS/IE interface

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Types of nodes

• (Node (IN_List OUT_List))
• N1 Suspect (Alecu) (N1, ( (N2) (N3) ) )
• N2 Beneficiar (Alecu)
• N3 Alibi(Alecu)

Rau Alecu IN
Unjustified assumption (Assumption)
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Types of nodes

• Premise nodes always true (IN)
• Unjustified assumptions nodes (Assumptions)
  nodes which IE wants to believe (IN) or not
  (OUT), although they are not supported by the
  existing evidence
• Justified assumptions nodes (Regular nodes) -
  nodes which are believed only if there is a valid
  reason for that (a valid justification). An
  assumptions that has a valid justification is
  treated as a Regular node and is IN.
• Contradiction nodes always false (OUT)

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Data structures for a TMS

• Data structures
• (1) Node. Contains the following slots
• Value the representation of the associated
  fact a unique value, which is identical to the
  representation in the KB
• Label state of the node - IN or OUT.
• Type of node indicates the type of node
• NodeJustification list of justifications which
  justify the node. Note that a node may have
  several justifications
• IsConsequence list of justifications in which
  the node take part. It is formed of 2 lists
• ConsecIN list of justifications in which the
  node appears in the IN list
• ConsecOUT - list of justifications in which the
  node appears in the OUT list

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Data structures for a TMS

• (2) Justification. Contains the following slots
• Type represents the inference type of a
  justification, namely premise, Modus Ponens,
  rule, inheritance, etc. Depends on the Inference
  Engine and it is given by the IE to the TMS
• Consequence the node the justification
  justifies
• Premises list of nodes that participated in the
  inference, formed of the INList of nodes and the
  OUTList of nodes
• (3) An indexing structure and mechanism to allow
  fast search of nodes in the TMS

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TMS/IE responsibilities

• Responsibilities of the TMS
• Cashes beliefs and maintains node labels
• Detects contradictions
• Performs belief revision
• Generates explanations

• Responsibilities of the IE
• Adds premises and makes assumptions
• Apply rules and adds justifications
• Retracts assumptions
• Provides advise on handling contradictions

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TMS/IE interface

• IE action
• A. Provides a mapping between IE and TMS data
  structures
• If a new node is needed, IE must inform TMS about
  it, and give the connection between this node and
  the corresponding assertions.
• To use TMS nodes, IE must be able to retrieve TMS
  nodes associated with assertions that IE works
  with.
• IE must provide a way for defining nodes as
  premises, and for enabling/retracting assumptions.

• TMS action
• A. Creates nodes with specified properties

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TMS/IE interface

• IE action
• B. Provides facilities for representing
  justifications.
• C. Provides facilities for inspecting TMS
  beliefs, i.e. accessing label information.

• TMS action
• B. Accepts records of IE deductions (as
  justifications)
• C. Computes the correct label for nodes and
  supplies them on request.
• Derives consequences of assumptions premises
  based on the dependency network
• When assumptions are retracted, their
  consequences are retracted
• Provides explanations for beliefs, e.g.,
  inferences

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TMS/IE interface

• TMS action
• D. Detects contradictions, based on
  contradiction nodes and explicit dependencies.

• IE action
• D. Provides facilities for contradiction
  handling.

Ensuring a proper mapping between IE and TMS
structures Assertion i
Cash assertion i Node
I TMS network
Belief status for Node i