diff --git a/src/main/java/fr/inria/corese/core/next/data/api/support/term/IRIUtils.java b/src/main/java/fr/inria/corese/core/next/data/api/support/term/IRIUtils.java
index b629c1d79..0873cf08a 100644
--- a/src/main/java/fr/inria/corese/core/next/data/api/support/term/IRIUtils.java
+++ b/src/main/java/fr/inria/corese/core/next/data/api/support/term/IRIUtils.java
@@ -121,8 +121,8 @@ public static String guessLocalName(String iri) {
             if (matcher == null || !matcher.matches()) {
                 return iri;
             } else if (matcher.matches()) {
-                if (matcher.group("fragment") != null) { // If the IRI has a fragment
-                    return matcher.group("fragment");
+                if (matcher.group("anchor") != null) {
+                    return matcher.group("fragment") != null ? matcher.group("fragment") : "";
                 } else if (matcher.group(FINAL_PATH_GROUP) != null) { // If the IRI has no fragment but does not end with a slash
                     return matcher.group(FINAL_PATH_GROUP);
                 } else { // If the URI ends with a slash
diff --git a/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParser.java b/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParser.java
index 6d187f56f..ea9b51c29 100644
--- a/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParser.java
+++ b/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParser.java
@@ -46,8 +46,8 @@ public class RDFaParser extends AbstractRDFParser {
 
     private String baseIri = IOConstants.getDefaultBaseURI();
 
-    private SAXParser saxParser;
-    private SAXParserFactory saxParserFactory;
+    private final SAXParser saxParser;
+    private final SAXParserFactory saxParserFactory;
 
     /**
      * An index of IRI prefixes
@@ -249,7 +249,13 @@ && isAttributePresent(RDFaAttributes.HREF)) {
                     throw new ParsingException("Prefix '" + prefixName + "' contains underscore character which is not allowed in xmlns declaration");
                 }
 
-                IRI prefixNamespace = getValueFactory().createIRI(attributeValue, "");
+                IRI prefixNamespace;
+                if (IRIUtils.isStandardIRI(attributeValue)) {
+                    prefixNamespace = getValueFactory().createIRI(attributeValue);
+                } else {
+                    String baseIriString = currentProcessingContext().getEvaluationContext().getBaseIri().stringValue();
+                    prefixNamespace = getValueFactory().createIRI(baseIriString + attributeValue);
+                }
                 this.addIriMapping(prefixName, prefixNamespace);
             }
         });
diff --git a/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/support/AbstractTurtleTriGListener.java b/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/support/AbstractTurtleTriGListener.java
index 665ae131a..79ee33620 100644
--- a/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/support/AbstractTurtleTriGListener.java
+++ b/src/main/java/fr/inria/corese/core/next/data/impl/io/parser/support/AbstractTurtleTriGListener.java
@@ -138,6 +138,11 @@ public String resolveIRI(String raw) {
                 } else if (isAbsoluteIRI(raw)) {
                     return raw;
                 } else {
+                    if (prefix.isEmpty()) {
+                        throw new ParsingException(
+                                "Undeclared prefix: '' (empty prefix). " +
+                                        "Use '@prefix : <namespace> .' to declare it.");
+                    }
                     throw new ParsingException("Undeclared prefix: " + prefix);
                 }
             }
diff --git a/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParserTest.java b/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParserTest.java
index f383ebb58..63b8abb3b 100644
--- a/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParserTest.java
+++ b/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/rdfa/RDFaParserTest.java
@@ -511,6 +511,32 @@ void test429ErrorOnDTD() {
         assertTrue(testModel.contains(subject, RDF.type.getIRI(), object));
     }
 
+    @Test
+    void parseXmlnsWithRelativeUri() {
+        String xhtml = """
+                <?xml version="1.0" encoding="UTF-8"?>
+                <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
+                <html xmlns="http://www.w3.org/1999/xhtml"
+                      xmlns:ex="vocab#"
+                      version="XHTML+RDFa 1.1">
+                  <body>
+                    <p about="#me" typeof="ex:Person" property="ex:name">Alice</p>
+                  </body>
+                </html>""";
+
+        Model model = createTestModel();
+        RDFParser parser = parserFactory.createRDFParser(RDFFormat.RDFA, model, valueFactory);
+        parser.parse(new ByteArrayInputStream(xhtml.getBytes()), "http://example.org/test/");
+
+        IRI subject = valueFactory.createIRI("http://example.org/test/#me");
+        IRI type = RDF.type.getIRI();
+        IRI personClass = valueFactory.createIRI("http://example.org/test/vocab#Person");
+        IRI namePred = valueFactory.createIRI("http://example.org/test/vocab#name");
+
+        assertTrue(model.contains(subject, type, personClass));
+        assertTrue(model.contains(subject, namePred, valueFactory.createLiteral("Alice")));
+    }
+
     private static void logModelContent(Model model) {
         StringWriter outWriter = new StringWriter();
         RDFSerializer serializer = (new DefaultRDFSerializerFactory()).createSerializer(RDFFormat.TURTLE, model);
diff --git a/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/turtle/TurtleParserTest.java b/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/turtle/TurtleParserTest.java
index ce0c3be91..c1749b7a6 100644
--- a/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/turtle/TurtleParserTest.java
+++ b/src/test/java/fr/inria/corese/core/next/data/impl/io/parser/turtle/TurtleParserTest.java
@@ -114,4 +114,17 @@ void testRdfaManifest() {
         assertEquals(refModel.size(), model.size());
     }
 
+    @Test
+    void testUndeclaredEmptyPrefixThrowsParsingException() {
+        String turtle = ":subject :predicate :object .";
+        Model model = createTestModel();
+        RDFParser parser = new TurtleParser(model, factory);
+
+        fr.inria.corese.core.next.data.api.exception.ParsingException ex = org.junit.jupiter.api.Assertions.assertThrows(
+                fr.inria.corese.core.next.data.api.exception.ParsingException.class,
+                () -> parser.parse(new StringReader(turtle))
+        );
+        assertTrue(ex.getMessage().contains("Undeclared prefix: '' (empty prefix)"));
+    }
+
 }