X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FText%2FTradition%2FCollation%2FRelationshipStore.pm;h=4342bd98b79b209a991c37f034e8460a126a7095;hb=428bcf0bc79f77a7857b21ef881708faa792e33a;hp=f3fe5cbe1a717c2e3fa2c0d6fa74d59e0986f71e;hpb=a70370723615fd41e59a6b3e48d7afceb89ac288;p=scpubgit%2Fstemmatology.git

diff --git a/lib/Text/Tradition/Collation/RelationshipStore.pm b/lib/Text/Tradition/Collation/RelationshipStore.pm
index f3fe5cb..4342bd9 100644
--- a/lib/Text/Tradition/Collation/RelationshipStore.pm
+++ b/lib/Text/Tradition/Collation/RelationshipStore.pm
@@ -2,7 +2,9 @@ package Text::Tradition::Collation::RelationshipStore;
 
 use strict;
 use warnings;
+use Text::Tradition::Error;
 use Text::Tradition::Collation::Relationship;
+use TryCatch;
 
 use Moose;
 
@@ -18,6 +20,39 @@ texts, particularly medieval ones.  The RelationshipStore is an internal object
 of the collation, to keep track of the defined relationships (both specific and
 general) between readings.
 
+=begin testing
+
+use Text::Tradition;
+use TryCatch;
+
+use_ok( 'Text::Tradition::Collation::RelationshipStore' );
+
+# Add some relationships, and delete them
+
+my $cxfile = 't/data/Collatex-16.xml';
+my $t = Text::Tradition->new( 
+	'name'  => 'inline', 
+	'input' => 'CollateX',
+	'file'  => $cxfile,
+	);
+my $c = $t->collation;
+
+my @v1 = $c->add_relationship( 'n21', 'n22', { 'type' => 'lexical' } );
+is( scalar @v1, 1, "Added a single relationship" );
+is( $v1[0]->[0], 'n21', "Got correct node 1" );
+is( $v1[0]->[1], 'n22', "Got correct node 2" );
+my @v2 = $c->add_relationship( 'n24', 'n23', 
+	{ 'type' => 'spelling', 'scope' => 'global' } );
+is( scalar @v2, 2, "Added a global relationship with two instances" );
+@v1 = $c->del_relationship( 'n22', 'n21' );
+is( scalar @v1, 1, "Deleted first relationship" );
+@v2 = $c->del_relationship( 'n12', 'n13' );
+is( scalar @v2, 2, "Deleted second global relationship" );
+my @v3 = $c->del_relationship( 'n1', 'n2' );
+is( scalar @v3, 0, "Nothing deleted on non-existent relationship" );
+
+=end testing
+
 =head1 METHODS
 
 =head2 new( collation => $collation );
@@ -50,6 +85,91 @@ has 'graph' => (
     },
 	);
 	
+=head2 equivalence_graph()
+
+Returns an equivalence graph of the collation, in which all readings
+related via a 'colocated' relationship are transformed into a single
+vertex. Can be used to determine the validity of a new relationship. 
+
+=cut
+
+has 'equivalence_graph' => (
+	is => 'ro',
+	isa => 'Graph',
+	default => sub { Graph->new() },
+	writer => '_reset_equivalence',
+	);
+	
+has '_node_equivalences' => (
+	is => 'ro',
+	traits => ['Hash'],
+	handles => {
+		equivalence => 'get',
+		set_equivalence => 'set',
+		remove_equivalence => 'delete',
+		_clear_equivalence => 'clear',
+	},
+	);
+
+has '_equivalence_readings' => (
+	is => 'ro',
+	traits => ['Hash'],
+	handles => {
+		eqreadings => 'get',
+		set_eqreadings => 'set',
+		remove_eqreadings => 'delete',
+		_clear_eqreadings => 'clear',
+	},
+	);
+	
+around add_reading => sub {
+	my $orig = shift;
+	my $self = shift;
+	
+	$self->equivalence_graph->add_vertex( @_ );
+	$self->set_equivalence( $_[0], $_[0] );
+	$self->set_eqreadings( $_[0], [ $_[0] ] );
+	$self->$orig( @_ );
+};
+
+around delete_reading => sub {
+	my $orig = shift;
+	my $self = shift;
+	
+	$self->_remove_equivalence_node( @_ );
+	$self->$orig( @_ );
+};
+
+=head2 get_relationship
+
+Return the relationship object, if any, that exists between two readings.
+
+=cut
+
+sub get_relationship {
+	my $self = shift;
+	my @vector;
+	if( @_ == 1 && ref( $_[0] ) eq 'ARRAY' ) {
+		# Dereference the edge arrayref that was passed.
+		my $edge = shift;
+		@vector = @$edge;
+	} else {
+		@vector = @_;
+	}
+	my $relationship;
+	if( $self->graph->has_edge_attribute( @vector, 'object' ) ) {
+		$relationship = $self->graph->get_edge_attribute( @vector, 'object' );
+	} 
+	return $relationship;
+}
+
+sub _set_relationship {
+	my( $self, $relationship, @vector ) = @_;
+	$self->graph->add_edge( @vector );
+	$self->graph->set_edge_attribute( @vector, 'object', $relationship );
+	$self->_make_equivalence( @vector ) if $relationship->colocated;
+}
+
 =head2 create
 
 Create a new relationship with the given options and return it.
@@ -62,31 +182,23 @@ sub create {
 	# Check to see if a relationship exists between the two given readings
 	my $source = delete $options->{'orig_a'};
 	my $target = delete $options->{'orig_b'};
-	my $rel;
-	if( $self->graph->has_edge( $source, $target ) ) {
-		$rel = $self->graph->get_edge_attribute( $source, $target, 'object' );
-		if( $rel->type ne $options->{'type'} ) {
-			warn "Another relationship of type " . $rel->type 
-				. " already exists between $source and $target";
-			return;
+	my $rel = $self->get_relationship( $source, $target );
+	if( $rel ) {
+		if( $rel->type eq 'collated' ) {
+			# Always replace a 'collated' relationship with a more descriptive
+			# one, if asked.
+			$self->del_relationship( $source, $target );
+		} elsif( $rel->type ne $options->{'type'} ) {
+			throw( "Another relationship of type " . $rel->type 
+				. " already exists between $source and $target" );
 		} else {
 			return $rel;
 		}
 	}
 	
-	# Check to see if a nonlocal relationship is defined for the two readings
-	$rel = $self->scoped_relationship( $options->{'reading_a'}, 
-		$options->{'reading_b'} );
-	if( $rel && $rel->type eq $options->{'type'} ) {
-		return $rel;
-	} elsif( $rel ) {
-		warn sprintf( "Relationship of type %s with scope %s already defined for readings %s and %s", $rel->type, $rel->scope, $options->{'reading_a'}, $options->{'reading_b'} );
-		return;
-	} else {
-		$rel = Text::Tradition::Collation::Relationship->new( $options );
-		$self->add_scoped_relationship( $rel ) if $rel->nonlocal;
-		return $rel;
-	}
+	$rel = Text::Tradition::Collation::Relationship->new( $options );
+	$self->add_scoped_relationship( $rel ) if $rel->nonlocal;
+	return $rel;
 }
 
 =head2 add_scoped_relationship( $rel )
@@ -98,13 +210,16 @@ non-locally.  Key on whichever reading occurs first alphabetically.
 
 sub add_scoped_relationship {
 	my( $self, $rel ) = @_;
-	my $r = $self->scoped_relationship( $rel->reading_a, $rel->reading_b );
+	my $rdga = $rel->type eq 'orthographic' ? $rel->reading_a : lc( $rel->reading_a );
+	my $rdgb = $rel->type eq 'orthographic' ? $rel->reading_b : lc( $rel->reading_b );	
+	my $r = $self->scoped_relationship( $rdga, $rdgb );
 	if( $r ) {
 		warn sprintf( "Scoped relationship of type %s already exists between %s and %s",
-			$r->type, $rel->reading_a, $rel->reading_b );
+			$r->type, $rdga, $rdgb );
 		return;
 	}
-	$self->scopedrels->{$rel->reading_a}->{$rel->reading_b} = $rel;
+	my( $first, $second ) = sort ( $rdga, $rdgb );
+	$self->scopedrels->{$first}->{$second} = $rel;
 }
 
 =head2 scoped_relationship( $reading_a, $reading_b )
@@ -117,8 +232,12 @@ between the two reading strings. Returns undef if there is no general relationsh
 sub scoped_relationship {
 	my( $self, $rdga, $rdgb ) = @_;
 	my( $first, $second ) = sort( $rdga, $rdgb );
+	my( $lcfirst, $lcsecond ) = sort( lc( $rdga ), lc( $rdgb ) );
 	if( exists $self->scopedrels->{$first}->{$second} ) {
 		return $self->scopedrels->{$first}->{$second};
+	} elsif( exists $self->scopedrels->{$lcfirst}->{$lcsecond} ) {
+		my $rel = $self->scopedrels->{$lcfirst}->{$lcsecond};
+		return $rel->type ne 'orthographic' ? $rel : undef;
 	} else {
 		return undef;
 	}
@@ -134,73 +253,353 @@ scoped non-locally.
 Returns a status boolean and a list of all reading pairs connected by the call to
 add_relationship.
 
-=cut
+=begin testing
 
-sub add_relationship {
-	my( $self, $source, $source_rdg, $target, $target_rdg, $options ) = @_;
+use Test::Warn;
+use Text::Tradition;
+use TryCatch;
+
+my $t1;
+warning_is {
+	$t1 = Text::Tradition->new( 'input' => 'Self', 'file' => 't/data/legendfrag.xml' );
+} 'DROPPING r14.2 -> r8.1: Cannot set relationship on a meta reading',
+	"Got expected relationship drop warning on parse";
+
+# Test 1.1: try to equate nodes that are prevented with an intermediate collation
+ok( $t1, "Parsed test fragment file" );
+my $c1 = $t1->collation;
+my $trel = $c1->get_relationship( 'r9.2', 'r9.3' );
+is( ref( $trel ), 'Text::Tradition::Collation::Relationship',
+	"Troublesome relationship exists" );
+is( $trel->type, 'collated', "Troublesome relationship is a collation" );
+
+# Try to make the link we want
+try {
+	$c1->add_relationship( 'r8.6', 'r10.3', { 'type' => 'orthographic' } );
+	ok( 1, "Added cross-collation relationship as expected" );
+} catch( Text::Tradition::Error $e ) {
+	ok( 0, "Existing collation blocked equivalence relationship: " . $e->message );
+}
+
+try {
+	$c1->calculate_ranks();
+	ok( 1, "Successfully calculated ranks" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Collation now has a cycle: " . $e->message );
+}
 
-	# Check the options
-	$options->{'scope'} = 'local' unless $options->{'scope'};
+# Test 1.2: attempt merge of an identical reading
+try {
+	$c1->merge_readings( 'r9.3', 'r11.5' );
+	ok( 1, "Successfully merged reading 'pontifex'" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Merge of mergeable readings failed: $e->message" );
 	
-	my( $is_valid, $reason ) = 
-		$self->relationship_valid( $source, $target, $options->{'type'} );
-    unless( $is_valid ) {
-        return ( undef, $reason );
-    }
-    
-    # Try to create the relationship object.
-    $options->{'reading_a'} = $source_rdg->text;
-    $options->{'reading_b'} = $target_rdg->text;
-    $options->{'orig_a'} = $source;
-    $options->{'orig_b'} = $target;
-    my $relationship = $self->create( $options );
-	return( undef, "Relationship creation failed" ) unless $relationship;
+}
 
-	# Find all the pairs for which we need to set the relationship.
-	my @vectors = ( [ $source, $target ] );	
-    if( $relationship->colocated && $relationship->nonlocal ) {
-    	my $c = $self->collation;
-    	# Set the same relationship everywhere we can, throughout the graph.
-    	my @identical_readings = grep { $_->text eq $relationship->reading_a }
-    		$c->readings;
-    	foreach my $ir ( @identical_readings ) {
-    		next if $ir->id eq $source;
-    		# Check to see if there is a target reading with the same text at
-    		# the same rank.
-    		my @itarget = grep 
-    			{ $_->rank == $ir->rank && $_->text eq $relationship->reading_b }
-    			$c->readings;
-    		if( @itarget ) {
-    			# We found a hit.
-    			warn "More than one reading with text " . $target_rdg->text
-    				. " at rank " . $ir->rank . "!" if @itarget > 1;
-    			push( @vectors, [ $ir->id, $itarget[0]->id ] );
-    		}
-    	}	
+# Test 1.3: attempt relationship with a meta reading (should fail)
+try {
+	$c1->add_relationship( 'r8.1', 'r9.2', { 'type' => 'collated' } );
+	ok( 0, "Allowed a meta-reading to be used in a relationship" );
+} catch ( Text::Tradition::Error $e ) {
+	is( $e->message, 'Cannot set relationship on a meta reading', 
+		"Relationship link prevented for a meta reading" );
+}
+
+# Test 1.4: try to break a relationship near a meta reading
+$c1->add_relationship( 'r7.6', 'r7.3', { type => 'orthographic' } );
+try {
+	$c1->del_relationship( 'r7.6', 'r7.7' );
+	$c1->del_relationship( 'r7.6', 'r7.3' );
+	ok( 1, "Relationship broken with a meta reading as neighbor" );
+} catch {
+	ok( 0, "Relationship deletion failed with a meta reading as neighbor" );
+}
+
+# Test 2.1: try to equate nodes that are prevented with a real intermediate
+# equivalence
+my $t2;
+warning_is {
+	$t2 = Text::Tradition->new( 'input' => 'Self', 'file' => 't/data/legendfrag.xml' );
+} 'DROPPING r14.2 -> r8.1: Cannot set relationship on a meta reading',
+	"Got expected relationship drop warning on parse";
+my $c2 = $t2->collation;
+$c2->add_relationship( 'r9.2', 'r9.3', { 'type' => 'lexical' } );
+my $trel2 = $c2->get_relationship( 'r9.2', 'r9.3' );
+is( ref( $trel2 ), 'Text::Tradition::Collation::Relationship',
+	"Created blocking relationship" );
+is( $trel2->type, 'lexical', "Blocking relationship is not a collation" );
+# This time the link ought to fail
+try {
+	$c2->add_relationship( 'r8.6', 'r10.3', { 'type' => 'orthographic' } );
+	ok( 0, "Added cross-equivalent bad relationship" );
+} catch ( Text::Tradition::Error $e ) {
+	like( $e->message, qr/witness loop/,
+		"Existing equivalence blocked crossing relationship" );
+}
+
+try {
+	$c2->calculate_ranks();
+	ok( 1, "Successfully calculated ranks" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Collation now has a cycle: " . $e->message );
+}
+
+# Test 3.1: make a straightforward pair of transpositions.
+my $t3 = Text::Tradition->new( 'input' => 'Self', 'file' => 't/data/lf2.xml' );
+# Test 1: try to equate nodes that are prevented with an intermediate collation
+my $c3 = $t3->collation;
+try {
+	$c3->add_relationship( 'r36.4', 'r38.3', { 'type' => 'transposition' } );
+	ok( 1, "Added straightforward transposition" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Failed to add normal transposition: " . $e->message );
+}
+try {
+	$c3->add_relationship( 'r36.3', 'r38.2', { 'type' => 'transposition' } );
+	ok( 1, "Added straightforward transposition complement" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Failed to add normal transposition complement: " . $e->message );
+}
+
+# Test 3.2: try to make a transposition that could be a parallel.
+try {
+	$c3->add_relationship( 'r28.2', 'r29.2', { 'type' => 'transposition' } );
+	ok( 0, "Added bad colocated transposition" );
+} catch ( Text::Tradition::Error $e ) {
+	like( $e->message, qr/Readings appear to be colocated/,
+		"Prevented bad colocated transposition" );
+}
+
+# Test 3.3: make the parallel, and then make the transposition again.
+try {
+	$c3->add_relationship( 'r28.3', 'r29.3', { 'type' => 'orthographic' } );
+	ok( 1, "Equated identical readings for transposition" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Failed to equate identical readings: " . $e->message );
+}
+try {
+	$c3->add_relationship( 'r28.2', 'r29.2', { 'type' => 'transposition' } );
+	ok( 1, "Added straightforward transposition complement" );
+} catch ( Text::Tradition::Error $e ) {
+	ok( 0, "Failed to add normal transposition complement: " . $e->message );
+}
+
+=end testing
+
+=cut
+
+sub add_relationship {
+	my( $self, $source, $target, $options ) = @_;
+    my $c = $self->collation;
+	my $sourceobj = $c->reading( $source );
+	my $targetobj = $c->reading( $target );
+	throw( "Adding self relationship at $source" ) if $source eq $target;
+	throw( "Cannot set relationship on a meta reading" )
+		if( $sourceobj->is_meta || $targetobj->is_meta );
+	my $relationship;
+	my $thispaironly;
+	my $droppedcolls = [];
+	if( ref( $options ) eq 'Text::Tradition::Collation::Relationship' ) {
+		$relationship = $options;
+		$thispaironly = 1;  # If existing rel, set only where asked.
+	} else {
+		# Check the options
+		$options->{'scope'} = 'local' unless $options->{'scope'};
+		$options->{'scope'} = 'local' if $options->{'type'} eq 'collated';
+		$options->{'scope'} = 'local' if $options->{'type'} eq 'transposition';
+		
+		my( $is_valid, $reason ) = $self->relationship_valid( $source, $target, 
+			$options->{'type'}, $droppedcolls );
+		unless( $is_valid ) {
+			throw( "Invalid relationship: $reason" );
+		}
+		
+		# Try to create the relationship object.
+		$options->{'reading_a'} = $sourceobj->text;
+		$options->{'reading_b'} = $targetobj->text;
+		$options->{'orig_a'} = $source;
+		$options->{'orig_b'} = $target;
+    	if( $options->{'scope'} ne 'local' ) {
+			# Is there a relationship with this a & b already?
+			# Case-insensitive for non-orthographics.
+			my $rdga = $options->{'reading_a'};
+			my $rdgb = $options->{'reading_b'};
+			my $otherrel = $self->scoped_relationship( $rdga, $rdgb );
+			if( $otherrel && $otherrel->type eq $options->{type}
+				&& $otherrel->scope eq $options->{scope} ) {
+				warn "Applying existing scoped relationship for $rdga / $rdgb";
+				$relationship = $otherrel;
+			} elsif( $otherrel ) {
+				throw( "Conflicting scoped relationship for $rdga / $rdgb at $source / $target" );
+			}
+    	}
+		$relationship = $self->create( $options ) unless $relationship;  # Will throw on error
     }
-    
+
+
     # Now set the relationship(s).
     my @pairs_set;
-    foreach my $v ( @vectors ) {
-    	if( $self->graph->has_edge( @$v ) ) {
-    		# Is it locally scoped?
-    		my $rel = $self->graph->get_edge_attribute( @$v, 'object' );
-    		if( $rel->nonlocal ) {
-    			# TODO I think we should not be able to get here.
-    			warn "Found conflicting relationship at @$v";
-    		} else {
-    			warn "Not overriding local relationship set at @$v";
-    			next;
-    		}
+	my $rel = $self->get_relationship( $source, $target );
+	my $skip;
+	if( $rel && $rel ne $relationship ) {
+		if( $rel->nonlocal ) {
+			throw( "Found conflicting relationship at $source - $target" );
+		} elsif( $rel->type ne 'collated' ) {
+			# Replace a collation relationship; leave any other sort in place.
+			my $r1ann = $rel->has_annotation ? $rel->annotation : '';
+			my $r2ann = $relationship->has_annotation ? $relationship->annotation : '';
+			unless( $rel->type eq $relationship->type && $r1ann eq $r2ann ) {
+				warn sprintf( "Not overriding local relationship %s with global %s " 
+					. "set at %s -> %s (%s -> %s)", $rel->type, $relationship->type,
+					$source, $target, $rel->reading_a, $rel->reading_b );
+				$skip = 1;
+			}
+		}
+	}
+	$self->_set_relationship( $relationship, $source, $target ) unless $skip;
+	push( @pairs_set, [ $source, $target ] );
+    
+	# Find all the pairs for which we need to set the relationship.
+    if( $relationship->colocated && $relationship->nonlocal && !$thispaironly ) {
+		push( @pairs_set, $self->add_global_relationship( $relationship ) );
+    }
+    # Finally, restore whatever collations we can, and return.
+    $self->_restore_collations( @$droppedcolls );
+    return @pairs_set;
+}
+
+=head2 add_global_relationship( $options, $skipvector )
+
+Adds the relationship specified wherever the relevant readings appear together 
+in the graph.  Options as in add_relationship above. 
+
+=cut
+
+sub add_global_relationship {
+	my( $self, $options ) = @_;
+	# First see if we are dealing with a relationship object already
+	my $relationship;
+	if( ref( $options ) eq 'Text::Tradition::Collation::Relationship' ) {
+		$relationship = $options;
+	} else {
+		# Then see if a scoped relationship already applies for the words.
+		my $scopedrel = $self->scoped_relationship( 
+			$options->{reading_a}, $options->{reading_b} );
+		$relationship = $scopedrel ? $scopedrel 
+			: $self->create( $options );
+	}
+	# Sanity checking
+	throw( "Relationship passed to add_global is not global" )
+		unless $relationship->nonlocal;
+	throw( "Relationship passed to add_global is not a valid global type" )
+		unless $relationship->colocated && $relationship->type ne 'collated';
+		
+	# Apply the relationship wherever it is valid
+	my @pairs_set;
+    foreach my $v ( $self->_find_applicable( $relationship ) ) {
+    	my $exists = $self->get_relationship( @$v );
+    	if( $exists && $exists->type ne 'collated' ) {
+    		throw( "Found conflicting relationship at @$v" )
+    			unless $exists->type eq $relationship->type
+    				&& $exists->scope eq $relationship->scope;
+    	} else {
+	    	my @added = $self->add_relationship( @$v, $relationship );
+    		push( @pairs_set, @added );
     	}
-    	$self->graph->add_edge( @$v );
-    	$self->graph->set_edge_attribute( @$v, 'object', $relationship );
-    	push( @pairs_set, $v );
     }
-    
-    return( 1, @pairs_set );
+	return @pairs_set;	
+}
+
+
+=head2 del_scoped_relationship( $reading_a, $reading_b )
+
+Returns the general (document-level or global) relationship that has been defined 
+between the two reading strings. Returns undef if there is no general relationship.
+
+=cut
+
+sub del_scoped_relationship {
+	my( $self, $rdga, $rdgb ) = @_;
+	my( $first, $second ) = sort( $rdga, $rdgb );
+	return delete $self->scopedrels->{$first}->{$second};
+}
+
+sub _find_applicable {
+	my( $self, $rel ) = @_;
+	my $c = $self->collation;
+	# TODO Someday we might use a case sensitive language.
+	my $lang = $c->tradition->language;
+	my @vectors;
+	my @identical_readings;
+	if( $rel->type eq 'orthographic' ) {
+		@identical_readings = grep { $_->text eq $rel->reading_a } 
+			$c->readings;
+	} else {
+		@identical_readings = grep { lc( $_->text ) eq lc( $rel->reading_a ) }
+			$c->readings;
+	}
+	foreach my $ir ( @identical_readings ) {
+		my @itarget;
+		if( $rel->type eq 'orthographic' ) {
+			@itarget = grep { $_->rank == $ir->rank 
+							  && $_->text eq $rel->reading_b } $c->readings;
+		} else {
+			@itarget = grep { $_->rank == $ir->rank 
+							  && lc( $_->text ) eq lc( $rel->reading_b ) } $c->readings;
+		}
+		if( @itarget ) {
+			# Warn if there is more than one hit with no orth link between them.
+			my $itmain = shift @itarget;
+			if( @itarget ) {
+				my %all_targets;
+				map { $all_targets{$_} = 1 } @itarget;
+				map { delete $all_targets{$_} } 
+					$self->related_readings( $itmain, 
+						sub { $_[0]->type eq 'orthographic' } );
+    			warn "More than one unrelated reading with text " . $itmain->text
+    				. " at rank " . $ir->rank . "!" if keys %all_targets;
+			}
+			push( @vectors, [ $ir->id, $itmain->id ] );
+		}
+	}
+	return @vectors;
+}
+
+=head2 del_relationship( $source, $target )
+
+Removes the relationship between the given readings. If the relationship is
+non-local, removes the relationship everywhere in the graph.
+
+=cut
+
+sub del_relationship {
+	my( $self, $source, $target ) = @_;
+	my $rel = $self->get_relationship( $source, $target );
+	return () unless $rel; # Nothing to delete; return an empty set.
+	my $colo = $rel->colocated;
+	my @vectors = ( [ $source, $target ] );
+	$self->_remove_relationship( $colo, $source, $target );
+	if( $rel->nonlocal ) {
+		# Remove the relationship wherever it occurs.
+		# Remove the relationship wherever it occurs.
+		my @rel_edges = grep { $self->get_relationship( @$_ ) == $rel }
+			$self->relationships;
+		foreach my $re ( @rel_edges ) {
+			$self->_remove_relationship( $colo, @$re );
+			push( @vectors, $re );
+		}
+		$self->del_scoped_relationship( $rel->reading_a, $rel->reading_b );
+	}
+	return @vectors;
 }
 
+sub _remove_relationship {
+	my( $self, $equiv, @vector ) = @_;
+	$self->graph->delete_edge( @vector );
+	$self->_break_equivalence( @vector ) if $equiv;
+}
+	
 =head2 relationship_valid( $source, $target, $type )
 
 Checks whether a relationship of type $type may exist between the readings given
@@ -210,11 +609,15 @@ a yes/no boolean and, if the answer is no, message gives the reason why.
 =cut
 
 sub relationship_valid {
-    my( $self, $source, $target, $rel ) = @_;
+    my( $self, $source, $target, $rel, $mustdrop ) = @_;
+    $mustdrop = [] unless $mustdrop; # in case we were passed nothing
     my $c = $self->collation;
-    if ( $rel eq 'transposition' || $rel eq 'repetition' ) {
+    ## Assume validity is okay if we are initializing from scratch.
+    return ( 1, "initializing" ) unless $c->tradition->_initialized;
+        if ( $rel eq 'transposition' || $rel eq 'repetition' ) {
 		# Check that the two readings do (for a repetition) or do not (for
 		# a transposition) appear in the same witness.
+		# TODO this might be called before witness paths are set...
 		my %seen_wits;
 		map { $seen_wits{$_} = 1 } $c->reading_witnesses( $source );
 		foreach my $w ( $c->reading_witnesses( $target ) ) {
@@ -222,49 +625,130 @@ sub relationship_valid {
 				return ( 0, "Readings both occur in witness $w" ) 
 					if $rel eq 'transposition';
 				return ( 1, "ok" ) if $rel eq 'repetition';
+			}
 		}
-		return $rel eq 'transposition' ? ( 1, "ok" )
-			: ( 0, "Readings occur only in distinct witnesses" );
+		return ( 0, "Readings occur only in distinct witnesses" )
+			if $rel eq 'repetition';
+	} 
+	if ( $rel eq 'transposition' ) {
+		# We also need to check both that the readings occur in distinct
+		# witnesses, and that they are not in the same place. That is,
+		# proposing to link them should cause a witness loop.
+		if( $self->test_equivalence( $source, $target ) ) {
+			return ( 0, "Readings appear to be colocated, not transposed" );
+		} else {
+			return ( 1, "ok" );
 		}
-	} else {
+		
+	} elsif( $rel ne 'repetition' ) {
 		# Check that linking the source and target in a relationship won't lead
-		# to a path loop for any witness.  First make a lookup table of all the
-		# readings related to either the source or the target.
-		my @proposed_related = ( $source, $target );
-		push( @proposed_related, $self->related_readings( $source, 'colocated' ) );
-		push( @proposed_related, $self->related_readings( $target, 'colocated' ) );
-		my %pr_ids;
-		map { $pr_ids{ $_ } = 1 } @proposed_related;
-	
-		# None of these proposed related readings should have a neighbor that
-		# is also in proposed_related.
-		foreach my $pr ( keys %pr_ids ) {
-			foreach my $neighbor( $c->sequence->neighbors( $pr ) ) {
-				return( 0, "Would relate neighboring readings $pr and $neighbor" )
-					if exists $pr_ids{$neighbor};
+		# to a path loop for any witness. 
+		# First, drop/stash any collations that might interfere
+		my $sourceobj = $c->reading( $source );
+		my $targetobj = $c->reading( $target );
+		my $sourcerank = $sourceobj->has_rank ? $sourceobj->rank : -1;
+		my $targetrank = $targetobj->has_rank ? $targetobj->rank : -1;
+		unless( $rel eq 'collated' || $sourcerank == $targetrank ) {
+			push( @$mustdrop, $self->_drop_collations( $source ) );
+			push( @$mustdrop, $self->_drop_collations( $target ) );
+			if( $c->end->has_rank ) {
+				foreach my $rk ( $sourcerank .. $targetrank ) {
+					map { push( @$mustdrop, $self->_drop_collations( $_->id ) ) }
+						$c->readings_at_rank( $rk );
+				}
 			}
-		}		
+		}
+		unless( $self->test_equivalence( $source, $target ) ) {
+			$self->_restore_collations( @$mustdrop );
+			return( 0, "Relationship would create witness loop" );
+		}
 		return ( 1, "ok" );
 	}
 }
 
-=head2 related_readings( $reading, $colocated_only )
+sub _drop_collations {
+	my( $self, $reading ) = @_;
+	my @dropped;
+	foreach my $n ( $self->graph->neighbors( $reading ) ) {
+		if( $self->get_relationship( $reading, $n )->type eq 'collated' ) {
+			push( @dropped, [ $reading, $n ] );
+			$self->del_relationship( $reading, $n );
+			#print STDERR "Dropped collation $reading -> $n\n";
+		}
+	}
+	return @dropped;
+}
+
+sub _restore_collations {
+	my( $self, @vectors ) = @_;
+	foreach my $v ( @vectors ) {
+		try {
+			$self->add_relationship( @$v, { 'type' => 'collated' } );
+			#print STDERR "Restored collation @$v\n";
+		} catch {
+			print STDERR $v->[0] . " - " . $v->[1] . " no longer collate\n";
+		}
+	}
+}
+
+=head2 filter_collations()
+
+Utility function. Removes any redundant 'collated' relationships from the graph.
+A collated relationship is redundant if the readings in question would occupy
+the same rank regardless of the existence of the relationship.
+
+=cut
+
+sub filter_collations {
+	my $self = shift;
+	my $c = $self->collation;
+	foreach my $r ( 1 .. $c->end->rank - 1 ) {
+		my $anchor;
+		my @need_collations;
+		foreach my $rdg ( $c->readings_at_rank( $r ) ) {
+			next if $rdg->is_meta;
+			my $ip = 0;
+			foreach my $pred ( $rdg->predecessors ) {
+				if( $pred->rank == $r - 1 ) {
+					$ip = 1;
+					$anchor = $rdg unless( $anchor );
+					last;
+				}
+			}
+			push( @need_collations, $rdg ) unless $ip;
+			$c->relations->_drop_collations( "$rdg" );
+		}
+		$anchor
+			? map { $c->add_relationship( $anchor, $_, { 'type' => 'collated' } )
+						unless $c->get_relationship( $anchor, $_ ) } @need_collations
+			: warn "No anchor found at $r";
+	}
+}
+
+=head2 related_readings( $reading, $filter )
 
 Returns a list of readings that are connected via relationship links to $reading.
-If $colocated_only is true, restricts the list to those readings that are in the
-same logical location (and therefore have the same rank in the collation graph.)
+If $filter is set to a subroutine ref, returns only those related readings where
+$filter( $relationship ) returns a true value.
 
 =cut
 
 sub related_readings {
-	my( $self, $reading, $colocated ) = @_;
+	my( $self, $reading, $filter ) = @_;
 	my $return_object;
 	if( ref( $reading ) eq 'Text::Tradition::Collation::Reading' ) {
 		$reading = $reading->id;
 		$return_object = 1;
 	}
 	my @answer;
-	if( $colocated ) {
+	if( $filter ) {
+		# Backwards compat
+		if( $filter eq 'colocated' ) {
+			$filter = sub { $_[0]->colocated };
+		} elsif( !ref( $filter ) ) {
+			my $type = $filter;
+			$filter = sub { $_[0]->type eq $type };
+		}
 		my %found = ( $reading => 1 );
 		my $check = [ $reading ];
 		my $iter = 0;
@@ -272,7 +756,7 @@ sub related_readings {
 			my $more = [];
 			foreach my $r ( @$check ) {
 				foreach my $nr ( $self->graph->neighbors( $r ) ) {
-					if( $self->graph->get_edge_attribute( $r, $nr, 'object' )->colocated ) {
+					if( &$filter( $self->get_relationship( $r, $nr ) ) ) {
 						push( @$more, $nr ) unless exists $found{$nr};
 						$found{$nr} = 1;
 					}
@@ -280,6 +764,7 @@ sub related_readings {
 			}
 			$check = $more;
 		}
+		delete $found{$reading};
 		@answer = keys %found;
 	} else {
 		@answer = $self->graph->all_reachable( $reading );
@@ -310,57 +795,397 @@ sub merge_readings {
 		# If kept changes its text, drop the relationship.
 		next if $combined;
 			
-		# If kept / rel already has a relationship, warn and keep the old
-		if( $self->graph->has_edge( @vector ) ) {
-			warn sprintf( "Readings %s and %s have existing relationship; dropping link with %s", @vector, $deleted );
-			next;
-		}
+		# If kept / rel already has a relationship, just keep the old
+		my $rel = $self->get_relationship( @vector );
+		next if $rel;
 		
 		# Otherwise, adopt the relationship that would be deleted.
-		my $rel = $self->graph->get_edge_attribute( @$edge, 'object' );
-		$self->graph->add_edge( @vector );
-		$self->graph->set_edge_attribute( @vector, 'object', $rel );
+		$rel = $self->get_relationship( @$edge );
+		$self->_set_relationship( $rel, @vector );
+	}
+	$self->_make_equivalence( $deleted, $kept );
+}
+
+### Equivalence logic
+
+sub _remove_equivalence_node {
+	my( $self, $node ) = @_;
+	my $group = $self->equivalence( $node );
+	my $nodelist = $self->eqreadings( $group );
+	if( @$nodelist == 1 && $nodelist->[0] eq $node ) {
+		$self->equivalence_graph->delete_vertex( $group );
+		$self->remove_eqreadings( $group );
+		$self->remove_equivalence( $group );
+	} elsif( @$nodelist == 1 ) {
+		throw( "DATA INCONSISTENCY in equivalence graph: " . $nodelist->[0] .
+			" in group that should have only $node" );
+	} else {
+ 		my @newlist = grep { $_ ne $node } @$nodelist;
+		$self->set_eqreadings( $group, \@newlist );
+		$self->remove_equivalence( $node );
+	}
+}
+
+=head2 add_equivalence_edge
+
+Add an edge in the equivalence graph corresponding to $source -> $target in the
+collation. Should only be called by Collation.
+
+=cut
+
+sub add_equivalence_edge {
+	my( $self, $source, $target ) = @_;
+	my $seq = $self->equivalence( $source );
+	my $teq = $self->equivalence( $target );
+	$self->equivalence_graph->add_edge( $seq, $teq );
+}
+
+=head2 delete_equivalence_edge
+
+Remove an edge in the equivalence graph corresponding to $source -> $target in the
+collation. Should only be called by Collation.
+
+=cut
+
+sub delete_equivalence_edge {
+	my( $self, $source, $target ) = @_;
+	my $seq = $self->equivalence( $source );
+	my $teq = $self->equivalence( $target );
+	$self->equivalence_graph->delete_edge( $seq, $teq );
+}
+
+sub _is_disconnected {
+	my $self = shift;
+	return( scalar $self->equivalence_graph->predecessorless_vertices > 1
+		|| scalar $self->equivalence_graph->successorless_vertices > 1 );
+}
+
+# Equate two readings in the equivalence graph
+sub _make_equivalence {
+	my( $self, $source, $target ) = @_;
+	# Get the source equivalent readings
+	my $seq = $self->equivalence( $source );
+	my $teq = $self->equivalence( $target );
+	# Nothing to do if they are already equivalent...
+	return if $seq eq $teq;
+	my $sourcepool = $self->eqreadings( $seq );
+	# and add them to the target readings.
+	push( @{$self->eqreadings( $teq )}, @$sourcepool );
+	map { $self->set_equivalence( $_, $teq ) } @$sourcepool;
+	# Then merge the nodes in the equivalence graph.
+	foreach my $pred ( $self->equivalence_graph->predecessors( $seq ) ) {
+		$self->equivalence_graph->add_edge( $pred, $teq );
+	}
+	foreach my $succ ( $self->equivalence_graph->successors( $seq ) ) {
+		$self->equivalence_graph->add_edge( $teq, $succ );
+	}
+	$self->equivalence_graph->delete_vertex( $seq );
+	# TODO enable this after collation parsing is done
+	throw( "Graph got disconnected making $source / $target equivalence" )
+		if $self->_is_disconnected && $self->collation->tradition->_initialized;
+}
+
+=head2 test_equivalence
+
+Test whether, if two readings were equated with a 'colocated' relationship, 
+the graph would still be valid.
+
+=cut
+
+sub test_equivalence {
+	my( $self, $source, $target ) = @_;
+	# Try merging the nodes in the equivalence graph; return a true value if
+	# no cycle is introduced thereby. Restore the original graph first.
+	
+	# Keep track of edges we add
+	my %added_pred;
+	my %added_succ;
+	# Get the reading equivalents
+	my $seq = $self->equivalence( $source );
+	my $teq = $self->equivalence( $target );
+	# Maybe this is easy?
+	return 1 if $seq eq $teq;
+	
+	# Save the first graph
+	my $checkstr = $self->equivalence_graph->stringify();
+	# Add and save relevant edges
+	foreach my $pred ( $self->equivalence_graph->predecessors( $seq ) ) {
+		if( $self->equivalence_graph->has_edge( $pred, $teq ) ) {
+			$added_pred{$pred} = 0;
+		} else {
+			$self->equivalence_graph->add_edge( $pred, $teq );
+			$added_pred{$pred} = 1;
+		}
+	}
+	foreach my $succ ( $self->equivalence_graph->successors( $seq ) ) {
+		if( $self->equivalence_graph->has_edge( $teq, $succ ) ) {
+			$added_succ{$succ} = 0;
+		} else {
+			$self->equivalence_graph->add_edge( $teq, $succ );
+			$added_succ{$succ} = 1;
+		}
+	}
+	# Delete source equivalent and test
+	$self->equivalence_graph->delete_vertex( $seq );
+	my $ret = !$self->equivalence_graph->has_a_cycle;
+	
+	# Restore what we changed
+	$self->equivalence_graph->add_vertex( $seq );
+	foreach my $pred ( keys %added_pred ) {
+		$self->equivalence_graph->add_edge( $pred, $seq );
+		$self->equivalence_graph->delete_edge( $pred, $teq ) if $added_pred{$pred};
+	}
+	foreach my $succ ( keys %added_succ ) {
+		$self->equivalence_graph->add_edge( $seq, $succ );
+		$self->equivalence_graph->delete_edge( $teq, $succ ) if $added_succ{$succ};
+	}
+	unless( $self->equivalence_graph->eq( $checkstr ) ) {
+		warn "GRAPH CHANGED after testing";
+	}
+	# Return our answer
+	return $ret;
+}
+
+# Unmake an equivalence link between two readings. Should only be called internally.
+sub _break_equivalence {
+	my( $self, $source, $target ) = @_;
+	
+	# This is the hard one. Need to reconstruct the equivalence groups without
+	# the given link.
+	my( %sng, %tng );
+	map { $sng{$_} = 1 } $self->_find_equiv_without( $source, $target );
+	map { $tng{$_} = 1 } $self->_find_equiv_without( $target, $source );
+	# If these groups intersect, they are still connected; do nothing.
+	foreach my $el ( keys %tng ) {
+		return if( exists $sng{$el} );
+	}
+	# If they don't intersect, then we split the nodes in the graph and in
+	# the hashes. First figure out which group has which name
+	my $oldgroup = $self->equivalence( $source ); # same as $target
+	my $keepsource = $sng{$oldgroup};
+	my $newgroup = $keepsource ? $target : $source;
+	my( $oldmembers, $newmembers );
+	if( $keepsource ) {
+		$oldmembers = [ keys %sng ];
+		$newmembers = [ keys %tng ];
+	} else {
+		$oldmembers = [ keys %tng ];
+		$newmembers = [ keys %sng ];
+	}
+		
+	# First alter the old group in the hash
+	$self->set_eqreadings( $oldgroup, $oldmembers );
+	foreach my $el ( @$oldmembers ) {
+		$self->set_equivalence( $el, $oldgroup );
+	}
+	
+	# then add the new group back to the hash with its new key
+	$self->set_eqreadings( $newgroup, $newmembers );
+	foreach my $el ( @$newmembers ) {
+		$self->set_equivalence( $el, $newgroup );
+	}
+	
+	# Now add the new group back to the equivalence graph
+	$self->equivalence_graph->add_vertex( $newgroup );
+	# ...add the appropriate edges to the source group vertext
+	my $c = $self->collation;
+	foreach my $rdg ( @$newmembers ) {
+		foreach my $rp ( $c->sequence->predecessors( $rdg ) ) {
+			next unless $self->equivalence( $rp );
+			$self->equivalence_graph->add_edge( $self->equivalence( $rp ), $newgroup );
+		}
+		foreach my $rs ( $c->sequence->successors( $rdg ) ) {
+			next unless $self->equivalence( $rs );
+			$self->equivalence_graph->add_edge( $newgroup, $self->equivalence( $rs ) );
+		}
+	}
+	
+	# ...and figure out which edges on the old group vertex to delete.
+	my( %old_pred, %old_succ );
+	foreach my $rdg ( @$oldmembers ) {
+		foreach my $rp ( $c->sequence->predecessors( $rdg ) ) {
+			next unless $self->equivalence( $rp );
+			$old_pred{$self->equivalence( $rp )} = 1;
+		}
+		foreach my $rs ( $c->sequence->successors( $rdg ) ) {
+			next unless $self->equivalence( $rs );
+			$old_succ{$self->equivalence( $rs )} = 1;
+		}
+	}
+	foreach my $p ( $self->equivalence_graph->predecessors( $oldgroup ) ) {
+		unless( $old_pred{$p} ) {
+			$self->equivalence_graph->delete_edge( $p, $oldgroup );
+		}
+	}
+	foreach my $s ( $self->equivalence_graph->successors( $oldgroup ) ) {
+		unless( $old_succ{$s} ) {
+			$self->equivalence_graph->delete_edge( $oldgroup, $s );
+		}
 	}
-	$self->delete_reading( $deleted );
+	# TODO enable this after collation parsing is done
+	throw( "Graph got disconnected breaking $source / $target equivalence" )
+		if $self->_is_disconnected && $self->collation->tradition->_initialized;
 }
 
-sub as_graphml { 
+sub _find_equiv_without {
+	my( $self, $first, $second ) = @_;
+	my %found = ( $first => 1 );
+	my $check = [ $first ];
+	my $iter = 0;
+	while( @$check ) {
+		my $more = [];
+		foreach my $r ( @$check ) {
+			foreach my $nr ( $self->graph->neighbors( $r ) ) {
+				next if $r eq $second;
+				if( $self->get_relationship( $r, $nr )->colocated ) {
+					push( @$more, $nr ) unless exists $found{$nr};
+					$found{$nr} = 1;
+				}
+			}
+		}
+		$check = $more;
+	}
+	return keys %found;
+}
+
+=head2 rebuild_equivalence
+
+(Re)build the equivalence graph from scratch. Dumps the graph, makes a new one,
+adds all readings and edges, then makes an equivalence for all relationships.
+
+=cut
+
+sub rebuild_equivalence {
+	my $self = shift;
+	my $newgraph = Graph->new();
+	# Set this as the new equivalence graph
+	$self->_reset_equivalence( $newgraph );
+	# Clear out the data hashes
+	$self->_clear_equivalence;
+	$self->_clear_eqreadings;
+	
+	$self->collation->tradition->_init_done(0);
+	# Add the readings
+	foreach my $r ( $self->collation->readings ) {
+		my $rid = $r->id;
+		$newgraph->add_vertex( $rid );
+		$self->set_equivalence( $rid, $rid );
+		$self->set_eqreadings( $rid, [ $rid ] );
+	}
+
+	# Now add the edges
+	foreach my $e ( $self->collation->paths ) {
+		$self->add_equivalence_edge( @$e );
+	}
+
+	# Now equate the colocated readings. This does no testing; 
+	# it assumes that all preexisting relationships are valid.
+	foreach my $rel ( $self->relationships ) {
+		my $relobj = $self->get_relationship( $rel );
+		next unless $relobj && $relobj->colocated;
+		$self->_make_equivalence( @$rel );
+	}
+	$self->collation->tradition->_init_done(1);
+}
+
+=head2 equivalence_ranks 
+
+Rank all vertices in the equivalence graph, and return a hash reference with
+vertex => rank mapping.
+
+=cut
+
+sub equivalence_ranks {
+	my $self = shift;
+	my $eqstart = $self->equivalence( $self->collation->start );
+	my $eqranks = { $eqstart => 0 };
+	my $rankeqs = { 0 => [ $eqstart ] };
+	my @curr_origin = ( $eqstart );
+    # A little iterative function.
+    while( @curr_origin ) {
+        @curr_origin = $self->_assign_rank( $eqranks, $rankeqs, @curr_origin );
+    }
+	return( $eqranks, $rankeqs );
+}
+
+sub _assign_rank {
+    my( $self, $node_ranks, $rank_nodes, @current_nodes ) = @_;
+    my $graph = $self->equivalence_graph;
+    # Look at each of the children of @current_nodes.  If all the child's 
+    # parents have a rank, assign it the highest rank + 1 and add it to 
+    # @next_nodes.  Otherwise skip it; we will return when the highest-ranked
+    # parent gets a rank.
+    my @next_nodes;
+    foreach my $c ( @current_nodes ) {
+        warn "Current reading $c has no rank!"
+            unless exists $node_ranks->{$c};
+        foreach my $child ( $graph->successors( $c ) ) {
+            next if exists $node_ranks->{$child};
+            my $highest_rank = -1;
+            my $skip = 0;
+            foreach my $parent ( $graph->predecessors( $child ) ) {
+                if( exists $node_ranks->{$parent} ) {
+                    $highest_rank = $node_ranks->{$parent} 
+                        if $highest_rank <= $node_ranks->{$parent};
+                } else {
+                    $skip = 1;
+                    last;
+                }
+            }
+            next if $skip;
+            my $c_rank = $highest_rank + 1;
+            # print STDERR "Assigning rank $c_rank to node $child \n";
+            $node_ranks->{$child} = $c_rank if $node_ranks;
+            push( @{$rank_nodes->{$c_rank}}, $child ) if $rank_nodes;
+            push( @next_nodes, $child );
+        }
+    }
+    return @next_nodes;
+}
+
+### Output logic
+
+sub _as_graphml { 
 	my( $self, $graphml_ns, $xmlroot, $node_hash, $nodeid_key, $edge_keys ) = @_;
 	
     my $rgraph = $xmlroot->addNewChild( $graphml_ns, 'graph' );
 	$rgraph->setAttribute( 'edgedefault', 'directed' );
     $rgraph->setAttribute( 'id', 'relationships', );
     $rgraph->setAttribute( 'parse.edgeids', 'canonical' );
-    $rgraph->setAttribute( 'parse.edges', scalar($self->graph->edges) );
+    $rgraph->setAttribute( 'parse.edges', 0 );
     $rgraph->setAttribute( 'parse.nodeids', 'canonical' );
-    $rgraph->setAttribute( 'parse.nodes', scalar($self->graph->vertices) );
+    $rgraph->setAttribute( 'parse.nodes', 0 );
     $rgraph->setAttribute( 'parse.order', 'nodesfirst' );
     
     # Add the vertices according to their XML IDs
     my %rdg_lookup = ( reverse %$node_hash );
-    foreach my $n ( sort _by_xmlid keys( %rdg_lookup ) ) {
+    # my @nlist = sort _by_xmlid keys( %rdg_lookup ); ## CAUSES SEGFAULT
+    my @nlist = sort keys( %rdg_lookup );
+    foreach my $n ( @nlist ) {
     	my $n_el = $rgraph->addNewChild( $graphml_ns, 'node' );
     	$n_el->setAttribute( 'id', $n );
     	_add_graphml_data( $n_el, $nodeid_key, $rdg_lookup{$n} );
     }
+	$rgraph->setAttribute( 'parse.nodes', scalar @nlist );
     
     # Add the relationship edges, with their object information
     my $edge_ctr = 0;
     foreach my $e ( sort { $a->[0] cmp $b->[0] } $self->graph->edges ) {
     	# Add an edge and fill in its relationship info.
+    	next unless( exists $node_hash->{$e->[0]} && exists $node_hash->{$e->[1]} );
 		my $edge_el = $rgraph->addNewChild( $graphml_ns, 'edge' );
 		$edge_el->setAttribute( 'source', $node_hash->{$e->[0]} );
 		$edge_el->setAttribute( 'target', $node_hash->{$e->[1]} );
 		$edge_el->setAttribute( 'id', 'e'.$edge_ctr++ );
 
-		my $rel_obj = $self->graph->get_edge_attribute( @$e, 'object' );
-		_add_graphml_data( $edge_el, $edge_keys->{'relationship'}, $rel_obj->type );
-		_add_graphml_data( $edge_el, $edge_keys->{'scope'}, $rel_obj->scope );
-		_add_graphml_data( $edge_el, $edge_keys->{'non_correctable'}, 
-			$rel_obj->non_correctable ) if $rel_obj->noncorr_set;
-		_add_graphml_data( $edge_el, $edge_keys->{'non_independent'}, 
-			$rel_obj->non_independent ) if $rel_obj->nonind_set;
+		my $rel_obj = $self->get_relationship( @$e );
+		foreach my $key ( keys %$edge_keys ) {
+			my $value = $rel_obj->$key;
+			_add_graphml_data( $edge_el, $edge_keys->{$key}, $value ) 
+				if defined $value;
+		}
 	}
+	$rgraph->setAttribute( 'parse.edges', $edge_ctr );
 }
 
 sub _by_xmlid {
@@ -379,6 +1204,13 @@ sub _add_graphml_data {
     $data_el->appendText( $value );
 }
 
+sub throw {
+	Text::Tradition::Error->throw( 
+		'ident' => 'Relationship error',
+		'message' => $_[0],
+		);
+}
+
 no Moose;
 __PACKAGE__->meta->make_immutable;