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		base     => $base,
		segments => $segments,
	       },$class;
}

sub smapped { 1; }

sub asString {
  shift->{base}->info;
}

sub type   { return 'similarity'; }

sub relative {
  my $self = shift;
  my $d = $self->{relative};
  $self->{relative} = shift if @_;
  $d;
}

sub segments {
  my $self = shift;
  return $self->{segments} ? @{$self->{segments}} : () unless $self->relative;
  # otherwise, we have to handle relative coordinates
  my $base   = $self->{base};
  my @e = map {Ace::Sequence->new(-refseq=>$base,-seq=>$_)} @{$self->{segments}};
  return $self->strand < 0 ? reverse @e : @e;
}

sub merged_segments {
  my $self = shift;

  return @{$self->{merged_segs}} if exists $self->{merged_segs};

  my @segs = sort {$a->start <=> $b->start} $self->segments;
  # attempt to merge overlapping segments
  my @merged;
  for my $s (@segs) {
    my $previous = $merged[-1];
    if ($previous && $previous->end+1 >= $s->start) {
      $previous->{length} = $s->end - $previous->start + 1;  # extend
    } else {
      my $clone = bless {%$s},ref($s);
      push @merged,$clone;
    }
  }
  $self->{merged_segs} = \@merged;
  return @merged;
}

1;

__END__

=head1 NAME

Ace::Sequence::GappedAlignment - Gapped alignment object

=head1 SYNOPSIS

    # open database connection and get an Ace::Sequence object
    use Ace::Sequence;

    # get a megabase from the middle of chromosome I
    $seq = Ace::Sequence->new(-name   => 'CHROMOSOME_I,
                              -db     => $db,
			      -offset => 3_000_000,
			      -length => 1_000_000);

    # get all the gapped alignments
    @alignments = $seq->alignments('EST_GENOME');

    # get the aligned segments from the first one
    @segs = $alignments[0]->segments;

    # get the position of the first aligned segment on the
    # source sequence:
    ($s_start,$s_end) = ($segs[0]->start,$segs[0]->end);

    # get the target position for the first aligned segment
    ($t_start,$t_end) = ($segs[0]->target->start,$segs[0]->target->end);

=head1 DESCRIPTION

Ace::Sequence::GappedAlignment is a subclass of
Ace::Sequence::Feature.  It inherits all the methods of
Ace::Sequence::Feature, but adds the ability to retrieve the positions
of the aligned segments.  Each segment is an Ace::Sequence::Feature,
from which you can retrieve the source and target coordinates.

=head1  OBJECT CREATION

You will not ordinarily create an I<Ace::Sequence::GappedAlignment>
object directly.  Instead, objects will be created in response to a
alignments() call to an I<Ace::Sequence> object.

=head1 OBJECT METHODS

Most methods are inherited from I<Ace::Sequence::Feature>.  The
following methods are also supported:

=over 4

=item segments()

  @segments = $gene->segments;

Return a list of Ace::Sequence::Feature objects corresponding to
similar segments.

=item relative()

  $relative = $gene->relative;
  $gene->relative(1);

This turns on and off relative coordinates.  By default, the exons and
intron features will be returned in the coordinate system used by the
gene.  If relative() is set to a true value, then coordinates will be
expressed as relative to the start of the gene.  The first exon will
(usually) be 1.