org.deri.iris.facts
Class FiniteUniverseFacts

java.lang.Object
  org.deri.iris.facts.FiniteUniverseFacts

All Implemented Interfaces:

IFacts

public class FiniteUniverseFacts
extends Object
implements IFacts

Definition: Unsafe negation A rule has a variable in a negated sub-goal that also occurs in the head, but nowhere else. Definition: Unsafe A rule has a variable that does not occur in a positive ordinary literal. Create a $UNIVERSE$(?X) relation. To handle unsafe negation (Gelder, Well-founded semantics, p.24): 1. For every rule, extract every occurrence of a non-ground-term, e.g. ?X or f(?Y) 2. Substitute a distinct ground term (not found anywhere else) for the variable(s), e.g. '$X', f('$Y') 3. Add this term to $UNIVERSE$ To handle all unsafe rules (with free variables in head or built-ins): 5. Add all concrete terms that occur anywhere in the program (facts and rules) to $UNIVERSE$ For both: 6. Add $UNIVERSE$(?variable) sub-goals for each free variable in each rule

Field Summary

static IPredicate

UNIVERSE The universe predicate.

Constructor Summary

FiniteUniverseFacts(IFacts facts, Collection<IRule> rules)
Constructor.

Method Summary

IRelation	get(IPredicate predicate) Get the relation associated with the given predicate and create one if one does not already exist.
Set<IPredicate>	getPredicates() Get the set of predicate identifying all relations known to this facts object.
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

UNIVERSE

public static final IPredicate UNIVERSE

The universe predicate.

Constructor Detail

FiniteUniverseFacts

public FiniteUniverseFacts(IFacts facts,
                           Collection<IRule> rules)

Constructor. Extract all ground terms from starting facts and rules.

Parameters:

facts - The starting facts of the knowledge-base.

rules - The rules of the knowledge-base.

Method Detail

get

public IRelation get(IPredicate predicate)

Description copied from interface: IFacts

Get the relation associated with the given predicate and create one if one does not already exist.

Specified by:

get in interface IFacts

Parameters:

predicate - The predicate identifying the relation.

Returns:

The relation associated with the given predicate.

getPredicates

public Set<IPredicate> getPredicates()

Description copied from interface: IFacts

Get the set of predicate identifying all relations known to this facts object.

Specified by:

getPredicates in interface IFacts

Returns:

toString

public String toString()

Overrides:

toString in class Object