Index: perl_lib/EPrints/MetaField/Compound.pm
===================================================================
--- perl_lib/EPrints/MetaField/Compound.pm	(revision 4411)
+++ perl_lib/EPrints/MetaField/Compound.pm	(working copy)
@@ -514,7 +514,11 @@
 	foreach my $field (@{$self->{fields_cache}})
 	{
 		my $name = $field->{sub_name};
-		my $element = $session->make_element( "xs:element", name => $name, type => $field->get_xml_schema_type() );
+		my $element = $session->make_element( "xs:element", 
+						      name => $name, 
+						      type => $field->get_xml_schema_type(), 
+						      minOccurs => 0
+		    );
 		$sequence->appendChild( $element );
 	}
 
Index: perl_lib/EPrints/MetaField/Set.pm
===================================================================
--- perl_lib/EPrints/MetaField/Set.pm	(revision 4410)
+++ perl_lib/EPrints/MetaField/Set.pm	(working copy)
@@ -568,6 +568,14 @@
 
 	my( $tags, $labels ) = $self->tags_and_labels( $session );
 
+	# Allow Set fields to have no value. This weakens the
+	# constraints applied by the schema but is an approach that
+	# works for the baseline scenario, that is, optional Set
+	# fields that may have been left unspecified where only weak
+	# constraints can be applied.
+	push @{$tags}, '';
+	$labels->{''} = $session->phrase( 'lib/metafield:unspecified' );
+
 	my $restriction = $session->make_element( "xs:restriction", base => "xs:string" );
 	$type->appendChild( $restriction );
 	foreach my $value (@$tags)
Index: perl_lib/EPrints/MetaField/Base64.pm
===================================================================
--- perl_lib/EPrints/MetaField/Base64.pm	(revision 4410)
+++ perl_lib/EPrints/MetaField/Base64.pm	(working copy)
@@ -74,5 +74,51 @@
 	return $tag;
 }
 
+sub get_xml_schema_type
+{
+    my( $self ) = @_;
+
+    return $self->get_property( "type" ) . "_" . $self->{dataset}->confid . "_" . $self->get_name;
+}
+
+sub render_xml_schema_type
+{
+    my( $self, $session ) = @_;
+    
+    # Returns DOM for the following:
+    #  <xs:complexType name="base64_file_data">
+    #    <xs:simpleContent>
+    #      <xs:extension base="xs:base64Binary">
+    #        <xs:attribute name="encoding">
+    #          <xs:simpleType>
+    #            <xs:restriction base="xs:string">
+    #              <xs:enumeration value="base64" />
+    #            </xs:restriction>
+    #          </xs:simpleType>
+    #        </xs:attribute>
+    #      </xs:extension>
+    #    </xs:simpleContent>
+    #  </xs:complexType>
+
+    my $type = $session->make_element( 'xs:complexType', name => $self->get_xml_schema_type );
+    my $sc = $session->make_element( 'xs:simpleContent' );
+    my $ext = $session->make_element( 'xs:extension', base => 'xs:base64Binary' );
+
+    # encoding attribute
+    my $encoding = $session->make_element( 'xs:attribute', name => 'encoding' );
+    my $enc_type = $session->make_element( 'xs:simpleType' );
+    my $enc_restr = $session->make_element( 'xs:restriction', base => 'xs:string' );
+    my $enc_enum = $session->make_element( 'xs:enumeration', value => 'base64' );
+
+    $enc_restr->appendChild( $enc_enum );
+    $enc_type->appendChild( $enc_restr );
+    $encoding->appendChild( $enc_type );
+    $ext->appendChild( $encoding );
+    $sc->appendChild( $ext );
+    $type->appendChild( $sc );
+
+    return $type;
+}
+
 ######################################################################
 1;