fix: resolve TTL export alias failure and add RDF notebook example (#355)

- Add _format_aliases map in RDFExporter to accept 'ttl', 'nt', 'xml', 'rdf', 'json-ld' as shorthands for canonical format names
- Resolve alias at the start of export_to_rdf() before validation, leaving all existing callers unaffected
- Add TTL alias demo cell to cookbook/introduction/15_Export.ipynb
- Add tests/export/test_rdf_exporter.py covering alias parity, canonical formats, unsupported format error, and file export with format="ttl"

Closes #355

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cookbook/introduction/15_Export.ipynb

@@ -178,6 +178,13 @@
     "rdf_exporter.export(kg, \"output.ttl\", format=\"turtle\")"
    ]
   },
+  {
+   "cell_type": "code",
+   "source": "# TTL alias: format=\"ttl\" is equivalent to format=\"turtle\"\nrdf_data = {\n    \"entities\": [\n        {\"id\": \"e1\", \"text\": \"Apple Inc.\", \"type\": \"ORG\", \"confidence\": 0.95},\n        {\"id\": \"e2\", \"text\": \"Steve Jobs\", \"type\": \"PERSON\", \"confidence\": 0.97},\n    ],\n    \"relationships\": [\n        {\"source_id\": \"e2\", \"target_id\": \"e1\", \"type\": \"founded_by\", \"confidence\": 0.91},\n    ],\n}\n\nrdf_exporter.export(rdf_data, \"output.ttl\", format=\"ttl\")\n\nresult = rdf_exporter.validate_rdf(rdf_data)\nprint(f\"Valid: {result['valid']}\")",
+   "metadata": {},
+   "execution_count": null,
+   "outputs": []
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -363,4 +370,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 2
-}
+}

semantica/export/rdf_exporter.py

@@ -851,6 +851,15 @@ class RDFExporter:
         # Supported RDF formats
         self.supported_formats = ["turtle", "rdfxml", "jsonld", "ntriples", "n3"]
 
+        # Format aliases (common extensions/shorthands → canonical names)
+        self._format_aliases = {
+            "ttl": "turtle",
+            "nt": "ntriples",
+            "xml": "rdfxml",
+            "rdf": "rdfxml",
+            "json-ld": "jsonld",
+        }
+
         # Initialize progress tracker
         self.progress_tracker = get_progress_tracker()
 
@@ -892,6 +901,7 @@ class RDFExporter:
         )
 
         try:
+            format = self._format_aliases.get(format.lower(), format.lower())
             if format not in self.supported_formats:
                 raise ValidationError(
                     f"Unsupported RDF format: {format}. "

tests/export/test_rdf_exporter.py

@@ -0,0 +1,73 @@
+"""Tests for RDFExporter format alias resolution (issue #355)."""
+
+import pytest
+from semantica.export import RDFExporter
+
+
+RDF_DATA = {
+    "entities": [
+        {"id": "e1", "text": "Apple Inc.", "type": "ORG", "confidence": 0.95},
+        {"id": "e2", "text": "Steve Jobs", "type": "PERSON", "confidence": 0.97},
+    ],
+    "relationships": [
+        {"source_id": "e2", "target_id": "e1", "type": "founded_by", "confidence": 0.91},
+    ],
+}
+
+
+@pytest.fixture
+def exporter():
+    return RDFExporter()
+
+
+def test_ttl_alias_produces_same_output_as_turtle(exporter):
+    """format='ttl' must produce identical output to format='turtle'."""
+    result_turtle = exporter.export_to_rdf(RDF_DATA, format="turtle")
+    result_ttl = exporter.export_to_rdf(RDF_DATA, format="ttl")
+    assert result_ttl == result_turtle
+
+
+def test_nt_alias_produces_same_output_as_ntriples(exporter):
+    result_canonical = exporter.export_to_rdf(RDF_DATA, format="ntriples")
+    result_alias = exporter.export_to_rdf(RDF_DATA, format="nt")
+    assert result_alias == result_canonical
+
+
+def test_xml_alias_produces_same_output_as_rdfxml(exporter):
+    result_canonical = exporter.export_to_rdf(RDF_DATA, format="rdfxml")
+    result_alias = exporter.export_to_rdf(RDF_DATA, format="xml")
+    assert result_alias == result_canonical
+
+
+def test_rdf_alias_produces_same_output_as_rdfxml(exporter):
+    result_canonical = exporter.export_to_rdf(RDF_DATA, format="rdfxml")
+    result_alias = exporter.export_to_rdf(RDF_DATA, format="rdf")
+    assert result_alias == result_canonical
+
+
+def test_json_ld_alias_produces_same_output_as_jsonld(exporter):
+    result_canonical = exporter.export_to_rdf(RDF_DATA, format="jsonld")
+    result_alias = exporter.export_to_rdf(RDF_DATA, format="json-ld")
+    assert result_alias == result_canonical
+
+
+def test_canonical_formats_unaffected(exporter):
+    """Existing canonical format names must continue to work."""
+    # n3 is listed in supported_formats but has no serializer implementation yet
+    for fmt in ("turtle", "rdfxml", "jsonld", "ntriples"):
+        result = exporter.export_to_rdf(RDF_DATA, format=fmt)
+        assert result is not None and len(result) > 0
+
+
+def test_unsupported_format_raises(exporter):
+    from semantica.utils.exceptions import ValidationError
+
+    with pytest.raises(ValidationError):
+        exporter.export_to_rdf(RDF_DATA, format="parquet")
+
+
+def test_ttl_export_to_file(exporter, tmp_path):
+    out = tmp_path / "output.ttl"
+    exporter.export(RDF_DATA, str(out), format="ttl")
+    assert out.exists()
+    assert out.stat().st_size > 0