/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/* Portions Copyright Aduna (http://www.aduna-software.com/) (c) 2007.
*
* Licensed under the Aduna BSD-style license.
*/
/*
* Created on Aug 8, 2011
*/
package com.bigdata.bop.solutions;
import info.aduna.lang.ObjectUtil;
import java.io.Serializable;
import java.util.Comparator;
import org.openrdf.model.Literal;
import org.openrdf.model.URI;
import org.openrdf.model.datatypes.XMLDatatypeUtil;
import org.openrdf.query.algebra.Compare.CompareOp;
import org.openrdf.query.algebra.evaluation.ValueExprEvaluationException;
import org.openrdf.query.algebra.evaluation.util.QueryEvaluationUtil;
import org.openrdf.query.algebra.evaluation.util.ValueComparator;
import com.bigdata.rdf.internal.IV;
import com.bigdata.rdf.internal.impl.bnode.SidIV;
import com.bigdata.rdf.internal.impl.literal.LiteralExtensionIV;
import com.bigdata.rdf.model.BigdataLiteral;
/**
* A comparator that compares {@link IV}s according the SPARQL value ordering as
* specified in <a
* href="http://www.w3.org/TR/rdf-sparql-query/#modOrderBy">SPARQL Query
* Language for RDF</a>. This implementation is based on the openrdf
* {@link ValueComparator} but has been modified to work with {@link IV}s.
* <p>
* Note: {@link SidIV} are blank nodes. However, we order SIDs after normal
* blank nodes since they are modeling somewhat different information.
*
* @author james
* @author Arjohn Kampman
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @author <a href="mailto:mrpersonick@users.sourceforge.net">Mike Personick</a>
* @version $Id$
*/
public class IVComparator implements Comparator<IV>, Serializable {
/**
*
*/
private static final long serialVersionUID = 1L;
@SuppressWarnings({ "rawtypes", "unchecked" })
public int compare(final IV o1, final IV o2) {
// check equality
if (ObjectUtil.nullEquals(o1, o2)) {
return 0;
}
// 1. (Lowest) no value assigned to the variable
if (o1 == null) {
return -1;
}
if (o2 == null) {
return 1;
}
// 2. Blank nodes
final boolean b1 = o1.isBNode();
final boolean b2 = o2.isBNode();
if (b1 && b2) {
return compareBNodes(o1, o2);
}
if (b1) {
return -1;
}
if (b2) {
return 1;
}
// 2.5 Statement identifiers (SIDs)
final boolean s1 = o1.isStatement();
final boolean s2 = o2.isStatement();
if (s1 && s2) {
return compareSIDs(o1, o2);
}
if (s1) {
return -1;
}
if (s2) {
return 1;
}
// 3. IRIs
final boolean u1 = o1.isURI();
final boolean u2 = o2.isURI();
if (u1 && u2) {
return compareURIs((URI) o1, (URI) o2);
}
if (u1) {
return -1;
}
if (u2) {
return 1;
}
// 4. RDF literals
return compareLiterals((IV<BigdataLiteral, ?>) o1,
(IV<BigdataLiteral, ?>) o2);
}
/**
* Use the natural ordering of the {@link IV}s when they are both blank
* nodes. This causes the solutions for the same blank node to be "grouped".
*
* @see <a href="http://www.openrdf.org/issues/browse/SES-873"> Order the
* same Blank Nodes together in ORDER BY</a>
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
private int compareBNodes(final IV leftBNode, final IV rightBNode) {
return leftBNode.compareTo(rightBNode);
}
/**
* Use the natural ordering of the {@link SidIV}s when they are both SIDs
* nodes. This causes the solutions for the same {@link SidIV} to be
* "grouped".
*
* @see <a href="https://sourceforge.net/apps/trac/bigdata/ticket/505">
* Exception when using SPARQL sort & statement identifiers </a>
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
private int compareSIDs(final IV leftSid, final IV rightSid) {
return leftSid.compareTo(rightSid);
}
/**
* Only difference here with Sesame ValueComparator is that we use
* stringValue() instead of toString().
*/
private int compareURIs(final URI leftURI, final URI rightURI) {
return leftURI.stringValue().compareTo(rightURI.stringValue());
}
private int compareLiterals(
final IV<BigdataLiteral, ?> left, final IV<BigdataLiteral, ?> right) {
/*
* Only thing we need to special case are LiteralExtensionIVs, which
* are used to model xsd:dateTime.
*/
if (left instanceof LiteralExtensionIV &&
right instanceof LiteralExtensionIV) {
@SuppressWarnings("rawtypes")
final IV leftDatatype = ((LiteralExtensionIV) left).getExtensionIV();
@SuppressWarnings("rawtypes")
final IV rightDatatype = ((LiteralExtensionIV) right).getExtensionIV();
if (leftDatatype.equals(rightDatatype)) {
return left.compareTo(right);
}
}
return compareLiterals((Literal) left, (Literal) right);
}
/**
* Taken directly from Sesame's ValueComparator, no modification. Handles
* inlines nicely since they now implement the Literal interface.
*/
private int compareLiterals(final Literal leftLit, final Literal rightLit) {
// Additional constraint for ORDER BY: "A plain literal is lower
// than an RDF literal with type xsd:string of the same lexical
// form."
if (!QueryEvaluationUtil.isStringLiteral(leftLit) || !QueryEvaluationUtil.isStringLiteral(rightLit)) {
try {
boolean isSmaller = QueryEvaluationUtil.compareLiterals(leftLit, rightLit, CompareOp.LT);
if (isSmaller) {
return -1;
}
else {
return 1;
}
}
catch (ValueExprEvaluationException e) {
// literals cannot be compared using the '<' operator, continue
// below
}
}
int result = 0;
// Sort by datatype first, plain literals come before datatyped literals
URI leftDatatype = leftLit.getDatatype();
URI rightDatatype = rightLit.getDatatype();
if (leftDatatype != null) {
if (rightDatatype != null) {
// Both literals have datatypes
result = compareDatatypes(leftDatatype, rightDatatype);
}
else {
result = 1;
}
}
else if (rightDatatype != null) {
result = -1;
}
if (result == 0) {
// datatypes are equal or both literals are untyped; sort by language
// tags, simple literals come before literals with language tags
String leftLanguage = leftLit.getLanguage();
String rightLanguage = rightLit.getLanguage();
if (leftLanguage != null) {
if (rightLanguage != null) {
result = leftLanguage.compareTo(rightLanguage);
}
else {
result = 1;
}
}
else if (rightLanguage != null) {
result = -1;
}
}
if (result == 0) {
// Literals are equal as fas as their datatypes and language tags are
// concerned, compare their labels
result = leftLit.getLabel().compareTo(rightLit.getLabel());
}
return result;
}
/**
* Taken directly from Sesame's ValueComparator, no modification.
*/
private int compareDatatypes(final URI leftDatatype, final URI rightDatatype) {
if (XMLDatatypeUtil.isNumericDatatype(leftDatatype)) {
if (XMLDatatypeUtil.isNumericDatatype(rightDatatype)) {
// both are numeric datatypes
return compareURIs(leftDatatype, rightDatatype);
}
else {
return -1;
}
}
else if (XMLDatatypeUtil.isNumericDatatype(rightDatatype)) {
return 1;
}
else if (XMLDatatypeUtil.isCalendarDatatype(leftDatatype)) {
if (XMLDatatypeUtil.isCalendarDatatype(rightDatatype)) {
// both are calendar datatypes
return compareURIs(leftDatatype, rightDatatype);
}
else {
return -1;
}
}
else if (XMLDatatypeUtil.isCalendarDatatype(rightDatatype)) {
return 1;
}
else {
// incompatible or unordered datatypes
return compareURIs(leftDatatype, rightDatatype);
}
}
}