GH-4066 refactor ProjectionElem to clarify use of targetName

This makes it clearer why this mechanism exists in addition to Extension
elements.

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/ArrayBindingBasedQueryEvaluationContext.java

@@ -14,7 +14,6 @@
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
-import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.function.BiConsumer;
@@ -271,8 +270,8 @@ public void meet(Var node) throws QueryEvaluationException {
  @Override
  public void meet(ProjectionElem node) throws QueryEvaluationException {
  super.meet(node);
- node.setSourceName(varNames.computeIfAbsent(node.getSourceName(), k -> k));
- node.setTargetName(varNames.computeIfAbsent(node.getTargetName(), k -> k));
+ node.setName(varNames.computeIfAbsent(node.getName(), k -> k));
+ node.setProjectionAlias(varNames.computeIfAbsent(node.getProjectionAlias().orElse(null), k -> k));
  }
 
  @Override

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/ConstantOptimizer.java

@@ -84,7 +84,7 @@ public void optimize(TupleExpr tupleExpr, Dataset dataset, BindingSet bindings)
  varsBefore.removeAll(varsAfter);
  for (ProjectionElemList projElems : visitor.projElemLists) {
  for (ProjectionElem projElem : projElems.getElements()) {
- String name = projElem.getSourceName();
+ String name = projElem.getName();
  if (varsBefore.contains(name)) {
  UnaryTupleOperator proj = (UnaryTupleOperator) projElems.getParentNode();
  Extension ext = new Extension(proj.getArg());

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/OrderLimitOptimizer.java

@@ -75,9 +75,7 @@ public void meet(Var node) {
  if (projection != null) {
  boolean projected = false;
  for (ProjectionElem e : projection.getProjectionElemList().getElements()) {
- String source = e.getSourceName();
- String target = e.getTargetName();
- if (node.getName().equals(source) && node.getName().equals(target)) {
+ if (node.getName().equals(e.getName())) {
  projected = true;
  break;
  }

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/impl/SameTermFilterOptimizer.java

@@ -187,8 +187,8 @@ public void meet(Var var) {
 
  @Override
  public void meet(ProjectionElem projElem) throws RuntimeException {
- if (projElem.getSourceName().equals(oldVar.getName())) {
- projElem.setSourceName(newVar.getName());
+ if (projElem.getName().equals(oldVar.getName())) {
+ projElem.setName(newVar.getName());
  }
  }
  }

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/iterator/ProjectionIterator.java

@@ -52,10 +52,9 @@ public ProjectionIterator(Projection projection, CloseableIteration<BindingSet,
 
  BiConsumer<MutableBindingSet, BindingSet> consumer = null;
  for (ProjectionElem pe : projectionElemList.getElements()) {
- String sourceName = pe.getSourceName();
- String targetName = pe.getTargetName();
- Function<BindingSet, Value> valueWithSourceName = context.getValue(sourceName);
- BiConsumer<Value, MutableBindingSet> setTarget = context.setBinding(targetName);
+ String projectionName = pe.getProjectionAlias().orElse(pe.getName());
+ Function<BindingSet, Value> valueWithSourceName = context.getValue(pe.getName());
+ BiConsumer<Value, MutableBindingSet> setTarget = context.setBinding(projectionName);
  BiConsumer<MutableBindingSet, BindingSet> next = (resultBindings, sourceBindings) -> {
  Value targetValue = valueWithSourceName.apply(sourceBindings);
  if (!includeAllParentBindings && targetValue == null) {
@@ -120,12 +119,12 @@ public static BindingSet project(ProjectionElemList projElemList, BindingSet sou
  final QueryBindingSet resultBindings = makeNewQueryBindings(parentBindings, includeAllParentBindings);
 
  for (ProjectionElem pe : projElemList.getElements()) {
- Value targetValue = sourceBindings.getValue(pe.getSourceName());
+ Value targetValue = sourceBindings.getValue(pe.getName());
  if (!includeAllParentBindings && targetValue == null) {
- targetValue = parentBindings.getValue(pe.getSourceName());
+ targetValue = parentBindings.getValue(pe.getName());
  }
  if (targetValue != null) {
- resultBindings.setBinding(pe.getTargetName(), targetValue);
+ resultBindings.setBinding(pe.getProjectionAlias().orElse(pe.getName()), targetValue);
  }
  }
 

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/optimizer/ConstantOptimizer.java

@@ -88,7 +88,7 @@ public void optimize(TupleExpr tupleExpr, Dataset dataset, BindingSet bindings)
  for (ProjectionElemList projElems : visitor.projElemLists) {
  for (ProjectionElem projElem : projElems.getElements()) {
 
- String name = projElem.getSourceName();
+ String name = projElem.getName();
 
  if (varsBefore.contains(name)) {
  UnaryTupleOperator proj = (UnaryTupleOperator) projElems.getParentNode();

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/optimizer/OrderLimitOptimizer.java

@@ -79,9 +79,7 @@ public void meet(Var node) {
  if (projection != null) {
  boolean projected = false;
  for (ProjectionElem e : projection.getProjectionElemList().getElements()) {
- String source = e.getSourceName();
- String target = e.getTargetName();
- if (node.getName().equals(source) && node.getName().equals(target)) {
+ if (node.getName().equals(e.getName())) {
  projected = true;
  break;
  }

core/queryalgebra/evaluation/src/main/java/org/eclipse/rdf4j/query/algebra/evaluation/optimizer/SameTermFilterOptimizer.java

@@ -191,8 +191,8 @@ public void meet(Var var) {
 
  @Override
  public void meet(ProjectionElem projElem) throws RuntimeException {
- if (projElem.getSourceName().equals(oldVar.getName())) {
- projElem.setSourceName(newVar.getName());
+ if (projElem.getName().equals(oldVar.getName())) {
+ projElem.setName(newVar.getName());
  }
  }
  }

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/MultiProjection.java

@@ -76,7 +76,7 @@ public Set<String> getBindingNames() {
  Set<String> bindingNames = new HashSet<>();
 
  for (ProjectionElemList projElemList : projections) {
- bindingNames.addAll(projElemList.getTargetNames());
+ bindingNames.addAll(projElemList.getProjectedNames());
  }
 
  return bindingNames;
@@ -89,10 +89,10 @@ public Set<String> getAssuredBindingNames() {
  if (projections.size() >= 1) {
  Set<String> assuredSourceNames = getArg().getAssuredBindingNames();
 
- bindingNames.addAll(projections.get(0).getTargetNamesFor(assuredSourceNames));
+ bindingNames.addAll(projections.get(0).getProjectedNamesFor(assuredSourceNames));
 
  for (int i = 1; i < projections.size(); i++) {
- bindingNames.retainAll(projections.get(i).getTargetNamesFor(assuredSourceNames));
+ bindingNames.retainAll(projections.get(i).getProjectedNamesFor(assuredSourceNames));
  }
  }
 

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/Projection.java

@@ -65,14 +65,14 @@ public void setProjectionElemList(ProjectionElemList projElemList) {
 
  @Override
  public Set<String> getBindingNames() {
- return projElemList.getTargetNames();
+ return projElemList.getProjectedNames();
  }
 
  @Override
  public Set<String> getAssuredBindingNames() {
  // Return all target binding names for which the source binding is assured
  // by the argument
- return projElemList.getTargetNamesFor(getArg().getAssuredBindingNames());
+ return projElemList.getProjectedNamesFor(getArg().getAssuredBindingNames());
  }
 
  @Override

core/queryalgebra/model/src/main/java/org/eclipse/rdf4j/query/algebra/ProjectionElem.java

@@ -10,56 +10,135 @@
  *******************************************************************************/
 package org.eclipse.rdf4j.query.algebra;
 
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Projection elements control which of the selected expressions (produced by the WHERE clause of a query) are returned
+ * in the solution, and the order in which they appear.
+ * <p>
+ * In SPARQL SELECT queries, projection elements are the variables determined by the algorithm for finding SELECT
+ * expressions (see <a href="https://www.w3.org/TR/sparql11-query/#sparqlSelectExpressions">SPARQL 1.1 Query Language
+ * Recommendation, section 18.2.4.4</a>). Each projection element will be a single variable name (any aliasing is
+ * handled by the use of {@link Extension}s).
+ * <p>
+ * In SPARQL CONSTRUCT queries, the projection elements are used to map the variables obtained from the SELECT
+ * expressions to the required statement patterns. In this case, each projection element will have an additional
+ * {@link #getProjectionAlias() target name} that maps each projection variable name to one of {@code subject},
+ * {@code predicate}, {@code object} or {@code context}.
+ * 
+ * @author Jeen Broekstra
+ */
 public class ProjectionElem extends AbstractQueryModelNode {
 
- /*-----------*
- * Variables *
- *-----------*/
+ private static final long serialVersionUID = -8129811335486478066L;
 
- private String sourceName;
+ private String name;
 
- private String targetName;
+ private String projectionAlias;
 
  private boolean aggregateOperatorInExpression;
 
  private ExtensionElem sourceExpression;
 
- /*--------------*
- * Constructors *
- *--------------*/
-
+ /**
+ * Create a new empty {@link ProjectionElem}.
+ */
  public ProjectionElem() {
  }
 
+ /**
+ * Create a new {@link ProjectionElem} with a variable name.
+ * 
+ * @param name The name of the projection element (typically the name of the variable in the select expressions).
+ * May not be <code>null</code>.
+ */
  public ProjectionElem(String name) {
- this(name, name);
+ this(name, null);
  }
 
- public ProjectionElem(String sourceName, String targetName) {
- setSourceName(sourceName);
- setTargetName(targetName);
+ /**
+ * Create a new {@link ProjectionElem} with a variable name and an additional mapped {@link #getProjectionAlias()
+ * target name}
+ * 
+ * @param name The name of the projection element (typically the name of the variable in the select
+ * expressions). May not be <code>null</code>.
+ * @param targetName The name of the variable the projection element value should be mapped to, to produce the
+ * projection. Used in CONSTRUCT queries for mapping select expressions to statement patterns. May
+ * be <code>null</code>.
+ */
+ public ProjectionElem(String name, String targetName) {
+ setName(name);
+ setProjectionAlias(targetName);
  }
 
- /*---------*
- * Methods *
- *---------*/
+ /**
+ * Get the name of the projection element (typically the name of the variable in the select expressions)
+ * 
+ */
+ public String getName() {
+ return name;
+ }
 
+ /**
+ * @deprecated since 4.1.1. Use {@link #getName()} instead.
+ */
+ @Deprecated(since = "4.1.1", forRemoval = true)
  public String getSourceName() {
- return sourceName;
+ return getName();
  }
 
+ /**
+ * @deprecated since 4.1.1. Use {@link #setName(String)} instead.
+ */
+ @Deprecated(since = "4.1.1", forRemoval = true)
  public void setSourceName(String sourceName) {
- assert sourceName != null : "sourceName must not be null";
- this.sourceName = sourceName;
+ setName(sourceName);
  }
 
- public String getTargetName() {
- return targetName;
+ /**
+ * Set the name of the projection element (typically the name of the variable in the select expressions)
+ * 
+ * @param name the projection variable name. May not be {@code null}.
+ */
+ public void setName(String name) {
+ this.name = Objects.requireNonNull(name);
+ }
+
+ /**
+ * Get the alias the projection element value should be mapped to. Used in CONSTRUCT queries for mapping select
+ * expressions to statement patterns.
+ * 
+ * @return an optionally empty projection alias.
+ */
+ public Optional<String> getProjectionAlias() {
+ return Optional.ofNullable(projectionAlias);
+ }
+
+ /**
+ * Set the alias the projection element value should be mapped to. Used in CONSTRUCT queries for mapping select
+ * expressions to statement patterns.
+ * 
+ * @param alias the projection alias.
+ */
+ public void setProjectionAlias(String alias) {
+ this.projectionAlias = alias;
  }
 
+ /**
+ * @deprecated since 4.1.1. Use {@link #setProjectionAlias(String)} instead.
+ */
+ @Deprecated(since = "4.1.1", forRemoval = true)
  public void setTargetName(String targetName) {
- assert targetName != null : "targetName must not be null";
- this.targetName = targetName;
+ setProjectionAlias(targetName);
+ }
+
+ /**
+ * @deprecated since 4.1.1. Use {@link #getProjectionAlias()} instead.
+ */
+ @Deprecated(since = "4.1.1", forRemoval = true)
+ public String getTargetName() {
+ return getProjectionAlias().orElse(null);
  }
 
  @Override
@@ -78,11 +157,11 @@ public String getSignature() {
  sb.append(super.getSignature());
 
  sb.append(" \"");
- sb.append(sourceName);
+ sb.append(name);
  sb.append("\"");
 
- if (!sourceName.equals(targetName)) {
- sb.append(" AS \"").append(targetName).append("\"");
+ if (projectionAlias != null) {
+ sb.append(" AS \"").append(projectionAlias).append("\"");
  }
 
  return sb.toString();
@@ -92,15 +171,14 @@ public String getSignature() {
  public boolean equals(Object other) {
  if (other instanceof ProjectionElem) {
  ProjectionElem o = (ProjectionElem) other;
- return sourceName.equals(o.getSourceName()) && targetName.equals(o.getTargetName());
+ return name.equals(o.getName()) && Objects.equals(getProjectionAlias(), o.getProjectionAlias());
  }
  return false;
  }
 
  @Override
  public int hashCode() {
- // Note: don't xor source and target since they will often be equal
- return targetName.hashCode();
+ return Objects.hash(name, projectionAlias);
  }
 
  @Override