Package nltk :: Package sem :: Module evaluate :: Class Model

type Model

object --+
         |
        Model

A first order model is a domain D of discourse and a valuation V.

A domain D is a set, and a valuation V is a map that associates expressions with values in the model. The domain of V should be a subset of D.

Instance Methods

[hide private]

__init__(self, domain, valuation)
Construct a new Model.

source code

__repr__(self)

source code

__str__(self)

source code

bool or 'Undefined'

evaluate(self, expr, g, trace=None)
Call the LogicParser to parse input expressions, and provide a handler for satisfy that blocks further propagation of the Undefined error. source code

satisfy(self, parsed, g, trace=None)
Recursive interpretation function for a formula of first-order logic.

source code

i(self, parsed, g, trace=False)
An interpretation function.

source code

satisfiers(self, parsed, varex, g, trace=None, nesting=0)
Generate the entities from the model's domain that satisfy an open formula.

source code

Method Details

[hide private]

init(self, domain, valuation)
(Constructor)

source code

Construct a new Model.

Parameters:

domain (set) - A set of entities representing the domain of discourse of the model.
valuation (Valuation) - the valuation of the model.
prop - If this is set, then we are building a propositional model and don't require the domain of V to be subset of D.

Overrides: object.__init__

repr(self)
(Representation operator)

source code

Overrides: object.__repr__: (inherited documentation)

str(self)
(Informal representation operator)

source code

Overrides: object.__str__: (inherited documentation)

evaluate(self, expr, g, trace=None)

source code

Call the LogicParser to parse input expressions, and provide a handler for satisfy that blocks further propagation of the Undefined error.

Parameters:

expr - An Expression of logic.
g (Assignment) - an assignment to individual variables.

Returns: bool or 'Undefined'

satisfy(self, parsed, g, trace=None)

source code

Recursive interpretation function for a formula of first-order logic.

Raises an Undefined error when parsed is an atomic string but is not a symbol or an individual variable.

Parameters:

parsed - An expression of logic.
g (Assignment) - an assignment to individual variables.

Returns:

Returns a truth value or Undefined if parsed is complex, and calls the interpretation function i if parsed is atomic.

i(self, parsed, g, trace=False)

source code

An interpretation function.

Assuming that parsed is atomic:

if parsed is a non-logical constant, calls the valuation V
else if parsed is an individual variable, calls assignment g
else returns Undefined.

Parameters:

parsed - an Expression of logic.
g (Assignment) - an assignment to individual variables.

Returns:

a semantic value

satisfiers(self, parsed, varex, g, trace=None, nesting=0)

source code

Generate the entities from the model's domain that satisfy an open formula.

Parameters:

parsed (Expression) - an open formula
varex (VariableExpression or str) - the relevant free individual variable in parsed.
g (Assignment) - a variable assignment

Returns:

a set of the entities that satisfy parsed.

type Model

__init__(self, domain, valuation) (Constructor)

__repr__(self) (Representation operator)

__str__(self) (Informal representation operator)

evaluate(self, expr, g, trace=None)

satisfy(self, parsed, g, trace=None)

i(self, parsed, g, trace=False)

satisfiers(self, parsed, varex, g, trace=None, nesting=0)

init(self, domain, valuation)
(Constructor)

repr(self)
(Representation operator)

str(self)
(Informal representation operator)