uk.ac.sheffield.vtts.model

Class Predicate

java.lang.Object

uk.ac.sheffield.vtts.model.Element

uk.ac.sheffield.vtts.model.Named

uk.ac.sheffield.vtts.model.Expression

uk.ac.sheffield.vtts.model.Function

uk.ac.sheffield.vtts.model.Predicate

Direct Known Subclasses:

Atomic, Comparison, Membership, Proposition

public abstract class Predicate
extends Function

Predicate represents a boolean valued function with a predicate root node. Predicate is the parent of different kinds of boolean-valued functions, such as Comparison (the inequality-testing predicate), Membership (the set and map membership testing predicate), Proposition (the combinatorial logic predicate) and Atomic (the degenerate atomic predicate). Any of Comparison, Membership and Proposition may be used in general expressions. Atomic is a special adapter that allows a Parameter to be treated like a Predicate, when testing for logical subsumption.

Version:

Broker@Cloud 1.0

Author:

Anthony J H Simons

Field Summary

Fields inherited from class uk.ac.sheffield.vtts.model.Function

expressions, maxOperands

Fields inherited from class uk.ac.sheffield.vtts.model.Expression

factory, type

Fields inherited from class uk.ac.sheffield.vtts.model.Named

name

Constructor Summary

Constructors

Constructor and Description
Predicate() Creates a default Predicate.
Predicate(java.lang.String name) Creates a named Predicate.

Method Summary

Methods

Modifier and Type	Method and Description
abstract java.lang.Boolean	evaluate() Evaluates this Predicate.
boolean	isConsistent() Reports whether this Predicate is consistent.
boolean	isFalseConstant() Reports whether this Predicate is the boolean constant false.
Predicate	negate() Returns the complement of this Predicate.
Predicate	normalise() Returns this Predicate in normal form.
void	rebind() Rebinds this Predicate, so that it may be tested for satisfaction.
void	rebind(java.lang.Object result) Rebinds the unbound operands of this Predicate, so that it yields the expected true or false result.
protected abstract void	rebindFalse() Rebinds the unbound operands of this Predicate, so that it yields false.
protected abstract void	rebindTrue() Rebinds the unbound operands of this Predicate, so that it yields true.
java.util.List<Predicate>	refine() Returns a list of refinements of this Predicate.
Predicate	setType(java.lang.String type) Sets the type of this Predicate.
abstract boolean	subsumes(Predicate other) Tests whether this Predicate subsumes the other Predicate.
protected boolean	subsumesAllDisjunctsOf(Proposition other) Tests whether this Predicate subsumes all disjuncts of the other OR-Proposition.
protected boolean	subsumesOneConjunctOf(Proposition other) Tests whether this Predicate subsumes one conjunct of the other AND-Proposition.
protected boolean	subsumesProposition(Proposition other) Tests whether this Predicate subsumes the other Proposition.

Methods inherited from class uk.ac.sheffield.vtts.model.Function

addExpression, assign, equals, getExpressions, getType, hashCode, isAssignable, isBound, nameCheck, operand, resolve, setName, toString, typeCheck, unbind

Methods inherited from class uk.ac.sheffield.vtts.model.Expression

getName, isBottom, isOrdered

Methods inherited from class uk.ac.sheffield.vtts.model.Named

setName

Methods inherited from class uk.ac.sheffield.vtts.model.Element

safeEquals, safeHashCode, semanticError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Predicate

public Predicate()

Creates a default Predicate. Sets the type to "Boolean".

Predicate

public Predicate(java.lang.String name)

Creates a named Predicate. Also sets the type to "Boolean".

Parameters:

name - the name of this Predicate.

Method Detail

setType

public Predicate setType(java.lang.String type)

Sets the type of this Predicate. Always sets the type to "Boolean", no matter what type was supplied (fail-safe).

Overrides:

setType in class Expression

Parameters:

type - the type to set.

Returns:

this Parameter.

evaluate

public abstract java.lang.Boolean evaluate()

Evaluates this Predicate. The result of evaluating any Predicate is always going to be a Boolean, rather than an Object type. Overrides the abstract method signature in Expression.

Specified by:

evaluate in class Expression

Returns:

true or false.

isConsistent

public boolean isConsistent()

Reports whether this Predicate is consistent. Returns true by default. Some kinds of predicate are able to determine if they are logically inconsistent, in which case this returns false.

Returns:

true if this Predicate is consistent.

isFalseConstant

public boolean isFalseConstant()

Reports whether this Predicate is the boolean constant false. Returns false by default, but is overridden in Atomic predicate , to return true for the wrapped Constant with the value false. This is used for subsumption checking in the degenerate case.

Returns:

true if this Predicate is the boolean constant false.

negate

public Predicate negate()

Returns the complement of this Predicate. By default, returns the constructed Proposition not(X) wrapping this Predicate X. Subclasses may have more specific and direct ways of expressing the complement, such as reversing an inequality.

Returns:

the complement of this Predicate.

normalise

public Predicate normalise()

Returns this Predicate in normal form. By default, returns this Predicate unchanged. In the Proposition subclass, simplifies the logical operators within a Proposition tree.

Returns:

the normalised form of this Predicate.

refine

public java.util.List<Predicate> refine()

Returns a list of refinements of this Predicate. By default, returns the singleton list containing this Predicate. Subclasses may have more subtle refinements, such as notEquals being converted into both lessThan and moreThan. This is used when calculating the symbolic partitions of the input space for an Operation.

Returns:

the refinements of this Predicate.

subsumes

public abstract boolean subsumes(Predicate other)

Tests whether this Predicate subsumes the other Predicate. Determines whether this Predicate is more general than the other Predicate, by a process of symbolic evaluation. Each of Comparison, Membership and Proposition uses a different subsumption algorithm. This is used when checking the guard conditions in every Scenario for possible blocking or non-determinism.

Parameters:

other - the other Predicate.

Returns:

true if this is more general than the other.

subsumesProposition

protected boolean subsumesProposition(Proposition other)

Tests whether this Predicate subsumes the other Proposition. This is useful in a number of subclasses of Predicate. Converts the other Proposition into normal form. If the result is an AND-Proposition, tests whether this Predicate subsumes one of the conjuncts. If the result is an OR-Proposition, tests whether this Predicate subsumes all of the disjuncts. If the result is a NOT-Proposition, reverses polarity and tests whether the negation of the other subsumes the negation of this. Returns false if this would lead to infinite regression.

Parameters:

other - the other Proposition.

Returns:

true, if this Predicate subsumes the other Proposition.

subsumesOneConjunctOf

protected boolean subsumesOneConjunctOf(Proposition other)

Tests whether this Predicate subsumes one conjunct of the other AND-Proposition. Uses the AND-splitting rule to determine whether this Predicate subsumes just one conjunct.

Parameters:

other - an AND-Proposition.

Returns:

true if this Predicate subsumes one conjunct.

subsumesAllDisjunctsOf

protected boolean subsumesAllDisjunctsOf(Proposition other)

Tests whether this Predicate subsumes all disjuncts of the other OR-Proposition. Uses the OR-merging rule to determine whether this Predicate subsumes all the disjuncts.

Parameters:

other - an OR-Proposition.

Returns:

true if this Predicate subsumes all disjuncts.

rebind

public void rebind()

Rebinds this Predicate, so that it may be tested for satisfaction. Rebinds the unbound operands of this Predicate, so that it yields true.

Overrides:

rebind in class Function

rebind

public void rebind(java.lang.Object result)

Rebinds the unbound operands of this Predicate, so that it yields the expected true or false result. This is a heuristic method, which may not always succeed, depending on other bound values.

Specified by:

rebind in class Expression

Parameters:

result - the expected true or false result of this Predicate.

rebindTrue

protected abstract void rebindTrue()

Rebinds the unbound operands of this Predicate, so that it yields true.

rebindFalse

protected abstract void rebindFalse()

Rebinds the unbound operands of this Predicate, so that it yields false.