it.unibz.inf.ontop.iq.transform.impl

Class NoNullValuesEnforcerImpl

java.lang.Object

it.unibz.inf.ontop.iq.transform.impl.NoNullValuesEnforcerImpl

All Implemented Interfaces:

IQTreeTransformer, NoNullValueEnforcer

public class NoNullValuesEnforcerImpl
extends Object
implements NoNullValueEnforcer

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	NoNullValuesEnforcerImpl.NotNullTopVariablePropagator

Method Summary

Modifier and Type	Method and Description
protected IQTree	declareTopVariablesNotNull(IQTree tree) Now that the filter has been inserted, we have the guarantee that the top variables are not nullable.
IQTree	transform(IQTree tree)

Methods inherited from class java.lang.Object

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

Method Detail

transform

public IQTree transform(IQTree tree)

Specified by:

transform in interface IQTreeTransformer

Specified by:

transform in interface NoNullValueEnforcer

declareTopVariablesNotNull

protected IQTree declareTopVariablesNotNull(IQTree tree)

Now that the filter has been inserted, we have the guarantee that the top variables are not nullable. Few functions like NULLIF can be simplified when they are declared as not able to produce a NULL. Not that such a simplification cannot always be performed using VariableNullability information (insufficient for NULLIF). For instance CONSTRUCT s,p,o s/RDF(a,IRI), p/RDF("http://ex.org/p", IRI), o/RDF(NULLIF(b, 0),xsd:integer) T1(a,b) becoming after inserting and pushing down the filter CONSTRUCT s,p,o s/RDF(a,IRI), p/RDF("http://ex.org/p", IRI), o/RDF(NULLIF(b, 0),xsd:integer) FILTER NOT(NON_STRICT_EQ(b, 0)) T1(a,b) Can be simplified as (by declaring "o" as non-null) CONSTRUCT s,p,o s/RDF(a,IRI), p/RDF("http://ex.org/p", IRI), o/RDF(b,xsd:integer) FILTER NOT(NON_STRICT_EQ(b, 0)) T1(a,b) DESIGN NOTE: In a bottom-up manner, NULLIF(b,0) would instead require to known that "b" is non-null *and different from 0* to simplify itself. Such information is only partially provided by the VariableNullability data structure.