Package edu.upc.fib.inlab.imp.kse.logics.logicschema.domain

Class Predicate

java.lang.Object

edu.upc.fib.inlab.imp.kse.logics.logicschema.domain.Predicate

Direct Known Subclasses:

MutablePredicate

public class Predicate
extends Object

Representation of a logic predicate. E.g. Predicate "Emp" with arity 2. A Predicate is a weak entity w.r.t. LogicSchema. That is:

• One Predicate can only belong to one LogicSchema
• A LogicSchema cannot contain two predicates with the same name

To instantiate a derived predicate, we use Queries, that is, a list of terms together a body For instance, if we have a mutable Predicate P, we can include some Queries to make it derived:

(x, y) :- R(x, y)

(x, w) :- S(x, w), T(w)

Do note that the queries do not require to include the predicate "P" on the head, since it would be redundant.

Field Summary

Fields

Modifier and Type	Field	Description
protected final List<DerivationRule>	derivationRules	Invariants: - name cannot be null - name cannot be empty - arity >= 0 - the list of derivationRules is not null - the list of derivationRules it not empty - derivationRules head terms size matches with arity - derivationRules are immutable when retrieved

Constructor Summary

Constructors

Constructor	Description
Predicate(String name, int arity)
Predicate(String name, int arity, List<Query> definitionQueries)

Method Summary

Modifier and Type	Method	Description
<T> T	accept(LogicSchemaVisitor<T> visitor)
int	getArity()
List<DerivationRule>	getDerivationRules()
DerivationRule	getFirstDerivationRule()
String	getName()
boolean	isBase()
boolean	isDerived()
boolean	isRecursive()	A predicate is recursive if it is derived and it appears in the body of its derivation rules, or in the body of some derivation rule it depends on.

Methods inherited from class java.lang.Object

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

Field Details

derivationRules

protected final List<DerivationRule> derivationRules

Invariants: - name cannot be null - name cannot be empty - arity >= 0 - the list of derivationRules is not null - the list of derivationRules it not empty - derivationRules head terms size matches with arity - derivationRules are immutable when retrieved

Constructor Details

Predicate

public Predicate(String name,
 int arity)

Predicate

public Predicate(String name,
 int arity,
 List<Query> definitionQueries)

Method Details

isRecursive

public boolean isRecursive()

A predicate is recursive if it is derived and it appears in the body of its derivation rules, or in the body of some derivation rule it depends on. E.g.:

R(x, y) :- R(x, z), R(z, y)

R(x, y) :- T(x, y)

P(x, y) :- R(x, z)

Q(x, y) :- S(x, y)

S(x, y) :- Q(x, y)

In this example, R, Q and S are recurisve predicate, but P and T are not.

Returns:

whether this predicate is recursive

getArity

public int getArity()

getName

public String getName()

getDerivationRules

public List<DerivationRule> getDerivationRules()

getFirstDerivationRule

public DerivationRule getFirstDerivationRule()

isDerived

public boolean isDerived()

isBase

public boolean isBase()

accept

public <T> T accept(LogicSchemaVisitor<T> visitor)