Lecture 3 - Supplement

TMS Functioning

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

Types of nodes

(Node (IN_List OUT_List))

N1 = Suspect (Alecu) (N1, ( (N2) (N3) ) )N2 = Beneficiar (Alecu)N3 = ~Alibi(Alecu)

Suspect Alecu [IN]

Beneficiar Alecu [IN] Alibi Alecu [OUT]

+ Lista IN Lista OUT

premisã aserþiune nejustificatã

justificare

aserþiune justificatã

Justification

JustifiedAssumption(Regular node)

Premise Unjustified assumption(Assumption)

Rau Alecu [IN]

Unjustified assumption(Assumption)

+

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)

Data structures for a TMSData 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

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

TMS/IE responsibilities

Responsibilities of the IE:

Adds premises and makes assumptions

Apply rules and adds justifications

Retracts assumptions Provides advise on

handling contradictions

Responsibilities of the TMS:

Cashes beliefs and maintains node labels

Detects contradictions Performs belief revision Generates explanations

TMS/IE interface IE action

A. Provides a mapping between IE and TMS data structures:

1. If a new node is needed, IE must inform TMS about it, and give the connection between this node and the corresponding assertions.

2. To use TMS nodes, IE must be able to retrieve TMS nodes associated with assertions that IE works with.

3. IE must provide a way for defining nodes as premises, and for enabling/retracting assumptions.

TMS action

A. Creates nodes with specified properties

TMS/IE interface IE action

B. Provides facilities for representing justifications.

C. Provides facilities for inspecting TMS beliefs, i.e. accessing label information.

TMS actionB. Accepts records of IE

deductions (as justifications)

C. Computes the correct label for nodes and supplies them on request.

1. Derives consequences of assumptions & premises based on the dependency network

2. When assumptions are retracted, their consequences are retracted

3. Provides explanations for beliefs, e.g., inferences

TMS/IE interface

IE action

D. Provides facilities for contradiction handling.

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