Lecture 3 - Supplement

1. Lecture 3 - Supplement TMS Functioning Content • Types of nodes • Data structures for a TMS • TMS/IE responsibilities • TMS/IE interface

2. Justified Assumption (Regular node) Justification Premise Unjustified assumption (Assumption) 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)

3. 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)

4. 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

5. 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

6. Responsibilities of the IE: Adds premises and makes assumptions Apply rules and adds justifications Retracts assumptions Provides advise on handling contradictions TMS/IE responsibilities • Responsibilities of the TMS: • Cashes beliefs and maintains node labels • Detects contradictions • Performs belief revision • Generates explanations

7. 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/IE interface • TMS action A. Creates nodes with specified properties

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

9. IE action D. Provides facilities for contradiction handling. TMS/IE interface • TMS action D. Detects contradictions, based on contradiction nodes and explicit dependencies. Ensuring a proper mapping between IE and TMS structures Assertion i Cash assertion i Node I TMS network Belief status for Node i