GH-5870: add basic RDF 1.2 support to FedX by aschwarte10 · Pull Request #5871 · eclipse-rdf4j/rdf4j

aschwarte10 · 2026-06-16T21:12:53Z

GitHub issue resolved: #5870

Commit 1: GH-5870: add initial RDF 1.2 support to FedX query optimizer (WIP)

Introduce TripleRefStatementPattern as a new FedX algebra node that
combines a StatementPattern with a TripleRef, representing SPARQL/RDF
1.2 reification patterns (rdf:reifies and embedded triple subjects).

Wire GenericInfoOptimizer to fold Join(TripleRef, StatementPattern) into
TripleRefStatementPattern via OptimizerUtil.flattenTripleRefJoins, and
register the resulting node in the statements list via meetOther.

Extend SourceSelection to handle FedXStatementPattern instances directly
(avoiding an unnecessary StatementSourcePattern wrapper), and update
QueryStringUtil to serialize the triple term syntax <<( ... )>> for
TripleRefStatementPattern.

Add unit tests for GenericInfoOptimizer covering three AST shapes, and
integration tests in RDF12Tests for single-source reification queries.

Note: TripleRefStatementPattern.evaluate() is not yet implemented;
federated (multi-source) RDF 1.2 query handling remains incomplete.

Commit 2: GH-5870: add initial RDF 1.2 support to FedX query optimizer (WIP)

Introduce TripleRefStatementPattern as a new FedX algebra node that
combines a StatementPattern with a TripleRef, representing SPARQL/RDF
1.2 reification patterns (rdf:reifies and embedded triple subjects).

Wire GenericInfoOptimizer to fold Join(TripleRef, StatementPattern) into
TripleRefStatementPattern via OptimizerUtil.flattenTripleRefJoins, and
register the resulting node in the statements list via meetOther.

Extend SourceSelection to handle FedXStatementPattern instances directly
(avoiding an unnecessary StatementSourcePattern wrapper), and update
QueryStringUtil to serialize the triple term syntax <<( ... )>> for
TripleRefStatementPattern.

Add unit tests for GenericInfoOptimizer covering three AST shapes, and
integration tests in RDF12Tests for single-source reification queries.

Note: TripleRefStatementPattern.evaluate() is not yet implemented;
federated (multi-source) RDF 1.2 query handling remains incomplete.

Commit 3: GH-5870: add end-to-end evaluation of TripleRefJoinGroup for RDF 1.2

Introduce enableTripleRefSupport config flag (default false) to gate RDF
1.2 triple term handling; both GenericInfoOptimizer
(flattenTripleRefJoins) and TripleRefJoinOptimizer only activate when
the flag is set, and GenericInfoOptimizer now tracks hasTripleRefExpr to
skip the latter pass when no triple ref patterns are present.

Generalize TripleRefJoinGroup and TripleRefStatementPattern from a
single StatementSource to List, removing the earlier
single-source assumption and enabling multi-source reification queries.

Wire evaluation of TripleRefJoinGroup into FederationEvaluationStrategy:
build a SELECT query via
QueryStringUtil.selectQueryStringTripleRefJoinGroup and dispatch it to
the assigned sources.

Add test data files for two endpoints and extend RDF12Tests with four
integration tests covering single- and multi-source reification joins in
both the rdf:reifies and embedded-triple-subject syntactic forms.

PR Author Checklist (see the contributor guidelines for more details):

my pull request is self-contained
I've added tests for the changes I made
I've applied code formatting (you can use mvn process-resources to format from the command line)
I've squashed my commits where necessary
every commit message starts with the issue number (GH-xxxx) followed by a meaningful description of the change

Introduce TripleRefStatementPattern as a new FedX algebra node that combines a StatementPattern with a TripleRef, representing SPARQL/RDF 1.2 reification patterns (rdf:reifies and embedded triple subjects). Wire GenericInfoOptimizer to fold Join(TripleRef, StatementPattern) into TripleRefStatementPattern via OptimizerUtil.flattenTripleRefJoins, and register the resulting node in the statements list via meetOther. Extend SourceSelection to handle FedXStatementPattern instances directly (avoiding an unnecessary StatementSourcePattern wrapper), and update QueryStringUtil to serialize the triple term syntax <<( ... )>> for TripleRefStatementPattern. Add unit tests for GenericInfoOptimizer covering three AST shapes, and integration tests in RDF12Tests for single-source reification queries. Note: TripleRefStatementPattern.evaluate() is not yet implemented; federated (multi-source) RDF 1.2 query handling remains incomplete.

Add TripleRefJoinGroup as a new algebra node that wraps a TripleRefStatementPattern together with co-located StatementPatterns sharing the same unbound subject variable, exclusive to a single source. Add TripleRefJoinOptimizer, which visits NJoin nodes depth-first and folds qualifying TripleRefStatementPattern + StatementPattern pairs into TripleRefJoinGroup instances. The grouping relies on the assumption that a shared unbound subject variable implies blank-node locality to a single dataset (no source-exclusivity check is performed). Wire the optimizer into FederationEvaluationStrategy after optimizeExclusiveExpressions (conditional invocation is TODO). Add getStatementSource() to TripleRefStatementPattern and extend RDF12Tests with a multi-source join test covering the new optimizer path.

Introduce enableTripleRefSupport config flag (default false) to gate RDF 1.2 triple term handling; both GenericInfoOptimizer (flattenTripleRefJoins) and TripleRefJoinOptimizer only activate when the flag is set, and GenericInfoOptimizer now tracks hasTripleRefExpr to skip the latter pass when no triple ref patterns are present. Generalize TripleRefJoinGroup and TripleRefStatementPattern from a single StatementSource to List<StatementSource>, removing the earlier single-source assumption and enabling multi-source reification queries. Wire evaluation of TripleRefJoinGroup into FederationEvaluationStrategy: build a SELECT query via QueryStringUtil.selectQueryStringTripleRefJoinGroup and dispatch it to the assigned sources. Add test data files for two endpoints and extend RDF12Tests with four integration tests covering single- and multi-source reification joins in both the rdf:reifies and embedded-triple-subject syntactic forms.

Copilot

Pull request overview

Adds initial RDF 1.2 “triple term” (reification / embedded triple) support to the FedX federation engine by introducing new algebra nodes and optimizations, plus query rendering and evaluation support, gated behind a configuration flag.

Changes:

Introduce TripleRefStatementPattern / TripleRefJoinGroup and related optimizers to recognize and group triple-term patterns for evaluation.
Extend FedX query serialization and evaluation strategy to generate and execute SPARQL queries containing RDF 1.2 triple term syntax.
Add RDF 1.2 federation integration tests + optimizer unit tests and test data.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
tools/federation/src/test/resources/tests/rdf1_2/data01endpoint2.ttl	Adds endpoint 2 RDF 1.2 reification test data
tools/federation/src/test/resources/tests/rdf1_2/data01endpoint1.ttl	Adds endpoint 1 RDF 1.2 reification test data
tools/federation/src/test/java/org/eclipse/rdf4j/federated/RDF12Tests.java	New integration tests for RDF 1.2 triple term queries in FedX
tools/federation/src/test/java/org/eclipse/rdf4j/federated/optimizer/GenericInfoOptimizerTest.java	New unit tests asserting optimizer rewrites into triple-term-aware nodes
tools/federation/src/test/java/org/eclipse/rdf4j/federated/FedXBaseTest.java	Normalizes anonymous variable names in query-plan assertions
tools/federation/src/main/java/org/eclipse/rdf4j/federated/util/QueryStringUtil.java	Adds query string generation for triple-term join groups and triple-term serialization
tools/federation/src/main/java/org/eclipse/rdf4j/federated/optimizer/TripleRefJoinOptimizer.java	New optimizer to group triple-term patterns with related statement patterns
tools/federation/src/main/java/org/eclipse/rdf4j/federated/optimizer/SourceSelection.java	Source selection updates to work directly with `FedXStatementPattern` instances
tools/federation/src/main/java/org/eclipse/rdf4j/federated/optimizer/OptimizerUtil.java	Adds join-flattening rewrite for triple-term join shapes
tools/federation/src/main/java/org/eclipse/rdf4j/federated/optimizer/GenericInfoOptimizer.java	Hooks triple-term rewrite into generic optimization and tracks presence of triple-term expressions
tools/federation/src/main/java/org/eclipse/rdf4j/federated/FedXConfig.java	Adds `enableTripleRefSupport` feature flag
tools/federation/src/main/java/org/eclipse/rdf4j/federated/evaluation/FederationEvaluationStrategy.java	Adds optimization + evaluation support for `TripleRefJoinGroup`
tools/federation/src/main/java/org/eclipse/rdf4j/federated/algebra/TripleRefStatementPattern.java	New algebra node combining statement pattern + `TripleRef`
tools/federation/src/main/java/org/eclipse/rdf4j/federated/algebra/TripleRefJoinGroup.java	New algebra node representing grouped triple-term join evaluation
tools/federation/src/main/java/org/eclipse/rdf4j/federated/algebra/StatementSourcePattern.java	Removes redundant `addStatementSource` (moved to base class)
tools/federation/src/main/java/org/eclipse/rdf4j/federated/algebra/FedXStatementPattern.java	Adds `addStatementSource` helper for reuse across statement pattern implementations

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aschwarte10 · 2026-06-17T05:46:15Z

+	public static TupleExpr flattenTripleRefJoins(Join join, QueryInfo queryInfo) {
+		// recursion
+		if (join.getLeftArg()instanceof Join nestedJoin) {
+			join.setLeftArg(flattenTripleRefJoins(nestedJoin, queryInfo));
+		}
+		if (join.getRightArg()instanceof Join nestedJoin) {
+			join.setRightArg(flattenTripleRefJoins(nestedJoin, queryInfo));
+		}
+
+		// handle own node
+		if (join.getLeftArg()instanceof TripleRef tr && join.getRightArg()instanceof StatementPattern stmt) {
+
+			TupleExpr newExpr = new TripleRefStatementPattern(stmt, tr, queryInfo);
+			return newExpr;
+		}
+		if (join.getRightArg()instanceof TripleRef tr && join.getLeftArg()instanceof StatementPattern stmt) {
+
+			TupleExpr newExpr = new TripleRefStatementPattern(stmt, tr, queryInfo);
+			return newExpr;
+		}
+
+		// leave actual join untouched
+		return join;
+	}


Actually this is generated by the spotless formatter for whatever reason and I need to retain it for passing the build ...

aschwarte10 · 2026-06-17T05:55:39Z

+		res.append("SELECT ");
+
+		for (String var : varNames) {
+			res.append(" ?").append(var);
+		}
+


not relevant in this case: varNames is expected to have one free var. If later we find cases where this is not the case, we need to resolve the join differently

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Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 5 comments.

aschwarte10 · 2026-06-17T07:22:29Z

+	@Override
+	public CloseableIteration<BindingSet> evaluate(BindingSet bindings) throws QueryEvaluationException {
+		// TODO Auto-generated method stub
+		return null;
+	}
+
+}


Copilot

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Copilot

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

+				assuredBindingNames.add(getContextVar().getName());
+			}
+
+			// Note: ; the statement's object var is an internal join id


aschwarte10 added 2 commits June 16, 2026 23:10

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Comment thread .../federation/src/main/java/org/eclipse/rdf4j/federated/algebra/TripleRefStatementPattern.java Outdated

GH-5870: Polishing and cleanup

a8b2761

aschwarte10 force-pushed the GH-5802-fedx-rdf12 branch from 15ad100 to a8b2761 Compare June 17, 2026 08:42

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Comment thread .../federation/src/main/java/org/eclipse/rdf4j/federated/algebra/TripleRefStatementPattern.java

assuredBindingNames.add(getContextVar().getName());

}

// Note: ; the statement's object var is an internal join id

aschwarte10 merged commit 388ff3a into develop Jun 17, 2026
14 checks passed

aschwarte10 deleted the GH-5802-fedx-rdf12 branch June 17, 2026 10:10

aschwarte10 mentioned this pull request Jun 17, 2026

Add basic initial RDF 1.2 support to FedX federation #5870

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aschwarte10 commented Jun 16, 2026 •

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