uk.ac.sheffield.vtts.model

Class Condition

java.lang.Object

uk.ac.sheffield.vtts.model.Element

uk.ac.sheffield.vtts.model.Condition

public class Condition
extends Element

Condition represents a logical guard, or a precondition. A Condition represents the logical precondition under which a particular Scenario is triggered. A Condition always contains a single Predicate, a logical expression, which may be defined in terms of the values of the Inputs of the Operation and of state Variables in Memory. The Condition's single Predicate is the formal constraint which must be satisfied for some Scenario to be triggered. A Condition may compare this Predicate symbolically against other Predicates, to test whether they are subsumed by the Condition's own Predicate. In this way, it can evaluate which symbolic constraints might be acceptable to its guard.

Version:

Broker@Cloud 1.0

Author:

Anthony J H Simons

Constructor Summary

Constructors

Constructor and Description
Condition() Creates a default Condition.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	accepts(Predicate actual) Determines whether this Condition would be satisfied by some actual constraint.
Condition	addPredicate(Predicate predicate) Adds the guard Predicate to this Condition.
boolean	evaluate() Evaluates this guard Condition, returning true or false.
Predicate	getComplement() Returns the complement of the guard Predicate.
java.util.Set<Predicate>	getPartitions() Returns the set of all possible atomic predicates and their negations that can be derived from this Condition's guard.
Predicate	getPredicate() Returns the Predicate guard.
Condition	resolve(Scope scope) Causes this Condition to resolve its global/local Parameter references.

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

safeEquals, safeHashCode, semanticError

Methods inherited from class java.lang.Object

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

Constructor Detail

Condition

public Condition()

Creates a default Condition.

Method Detail

addPredicate

public Condition addPredicate(Predicate predicate)

Adds the guard Predicate to this Condition.

Parameters:

predicate - the Predicate to attach.

Returns:

this Condition.

getPredicate

public Predicate getPredicate()

Returns the Predicate guard.

Returns:

the Predicate guard.

getComplement

public Predicate getComplement()

Returns the complement of the guard Predicate.

Returns:

the negation of the guard Predicate.

getPartitions

public java.util.Set<Predicate> getPartitions()

Returns the set of all possible atomic predicates and their negations that can be derived from this Condition's guard. The returned set is not structured in any way. The structuring of partitions is performed by Operation.

Returns:

a set of Predicates.

accepts

public boolean accepts(Predicate actual)

Determines whether this Condition would be satisfied by some actual constraint. The actual constraint must be defined in terms of the same Parameters as this Condition's guard. Returns true, if the guard subsumes the actual constraint.

Parameters:

actual - a Predicate representing an actual constraint.

Returns:

true if this Condition's formal Predicate subsumes the actual Predicate.

resolve

public Condition resolve(Scope scope)

Causes this Condition to resolve its global/local Parameter references.

Parameters:

scope - a table of global and local Parameters.

Returns:

this Condition.

evaluate

public boolean evaluate()

Evaluates this guard Condition, returning true or false. Evaluates the Predicate stored in this Condition. The Predicate may be any kind of boolean-valued expression, and may depend on bound Parameters, such as Variables, Inputs and Constants. Variables will have been bound at the start in Memory, and may also be modified by Effects. Inputs will have been bound at the start of the Scenario owning this Condition.

Returns:

true, if this Condition is satisfied.