Provided by: libbio-db-gff-perl_1.7.4-1_all 
NAME
Bio::DB::GFF::Feature -- A relative segment identified by a feature type
SYNOPSIS
See Bio::DB::GFF.
DESCRIPTION
Bio::DB::GFF::Feature is a stretch of sequence that corresponding to a single annotation
in a GFF database. It inherits from Bio::DB::GFF::RelSegment, and so has all the support
for relative addressing of this class and its ancestors. It also inherits from
Bio::SeqFeatureI and so has the familiar start(), stop(), primary_tag() and location()
methods (it implements Bio::LocationI too, if needed).
Bio::DB::GFF::Feature adds new methods to retrieve the annotation type, group, and other
GFF attributes. Annotation types are represented by Bio::DB::GFF::Typename objects, a
simple class that has two methods called method() and source(). These correspond to the
method and source fields of a GFF file.
Annotation groups serve the dual purpose of giving the annotation a human-readable name,
and providing higher-order groupings of subfeatures into features. The groups returned by
this module are objects of the Bio::DB::GFF::Featname class.
Bio::DB::GFF::Feature inherits from and implements the abstract methods of
Bio::SeqFeatureI, allowing it to interoperate with other Bioperl modules.
Generally, you will not create or manipulate Bio::DB::GFF::Feature objects directly, but
use those that are returned by the Bio::DB::GFF::RelSegment->features() method.
Important note about start() vs end()
If features are derived from segments that use relative addressing (which is the default),
then start() will be less than end() if the feature is on the opposite strand from the
reference sequence. This breaks Bio::SeqI compliance, but is necessary to avoid having
the real genomic locations designated by start() and end() swap places when changing
reference points.
To avoid this behavior, call $segment->absolute(1) before fetching features from it. This
will force everything into absolute coordinates.
For example:
my $segment = $db->segment('CHROMOSOME_I');
$segment->absolute(1);
my @features = $segment->features('transcript');
API
The remainder of this document describes the public and private methods implemented by
this module.
new_from_parent
Title : new_from_parent
Usage : $f = Bio::DB::GFF::Feature->new_from_parent(@args);
Function: create a new feature object
Returns : new Bio::DB::GFF::Feature object
Args : see below
Status : Internal
This method is called by Bio::DB::GFF to create a new feature using information obtained
from the GFF database. It is one of two similar constructors. This one is called when
the feature is generated from a RelSegment object, and should inherit the coordinate
system of that object.
The 13 arguments are positional (sorry):
$parent a Bio::DB::GFF::RelSegment object (or descendent)
$start start of this feature
$stop stop of this feature
$method this feature's GFF method
$source this feature's GFF source
$score this feature's score
$fstrand this feature's strand (relative to the source
sequence, which has its own strandedness!)
$phase this feature's phase
$group this feature's group (a Bio::DB::GFF::Featname object)
$db_id this feature's internal database ID
$group_id this feature's internal group database ID
$tstart this feature's target start
$tstop this feature's target stop
tstart and tstop are not used for anything at the moment, since the information is
embedded in the group object.
new
Title : new
Usage : $f = Bio::DB::GFF::Feature->new(@args);
Function: create a new feature object
Returns : new Bio::DB::GFF::Feature object
Args : see below
Status : Internal
This method is called by Bio::DB::GFF to create a new feature using information obtained
from the GFF database. It is one of two similar constructors. This one is called when
the feature is generated without reference to a RelSegment object, and should therefore
use its default coordinate system (relative to itself).
The 11 arguments are positional:
$factory a Bio::DB::GFF adaptor object (or descendent)
$srcseq the source sequence
$start start of this feature
$stop stop of this feature
$method this feature's GFF method
$source this feature's GFF source
$score this feature's score
$fstrand this feature's strand (relative to the source
sequence, which has its own strandedness!)
$phase this feature's phase
$group this feature's group
$db_id this feature's internal database ID
type
Title : type
Usage : $type = $f->type([$newtype])
Function: get or set the feature type
Returns : a Bio::DB::GFF::Typename object
Args : a new Typename object (optional)
Status : Public
This method gets or sets the type of the feature. The type is a Bio::DB::GFF::Typename
object, which encapsulates the feature method and source.
The method() and source() methods described next provide shortcuts to the individual
fields of the type.
method
Title : method
Usage : $method = $f->method([$newmethod])
Function: get or set the feature method
Returns : a string
Args : a new method (optional)
Status : Public
This method gets or sets the feature method. It is a convenience feature that delegates
the task to the feature's type object.
source
Title : source
Usage : $source = $f->source([$newsource])
Function: get or set the feature source
Returns : a string
Args : a new source (optional)
Status : Public
This method gets or sets the feature source. It is a convenience feature that delegates
the task to the feature's type object.
score
Title : score
Usage : $score = $f->score([$newscore])
Function: get or set the feature score
Returns : a string
Args : a new score (optional)
Status : Public
This method gets or sets the feature score.
phase
Title : phase
Usage : $phase = $f->phase([$phase])
Function: get or set the feature phase
Returns : a string
Args : a new phase (optional)
Status : Public
This method gets or sets the feature phase.
strand
Title : strand
Usage : $strand = $f->strand
Function: get the feature strand
Returns : +1, 0 -1
Args : none
Status : Public
Returns the strand of the feature. Unlike the other methods, the strand cannot be changed
once the object is created (due to coordinate considerations).
group
Title : group
Usage : $group = $f->group([$new_group])
Function: get or set the feature group
Returns : a Bio::DB::GFF::Featname object
Args : a new group (optional)
Status : Public
This method gets or sets the feature group. The group is a Bio::DB::GFF::Featname object,
which has an ID and a class.
display_id
Title : display_id
Usage : $display_id = $f->display_id([$display_id])
Function: get or set the feature display id
Returns : a Bio::DB::GFF::Featname object
Args : a new display_id (optional)
Status : Public
This method is an alias for group(). It is provided for Bio::SeqFeatureI compatibility.
info
Title : info
Usage : $info = $f->info([$new_info])
Function: get or set the feature group
Returns : a Bio::DB::GFF::Featname object
Args : a new group (optional)
Status : Public
This method is an alias for group(). It is provided for AcePerl compatibility.
target
Title : target
Usage : $target = $f->target([$new_target])
Function: get or set the feature target
Returns : a Bio::DB::GFF::Homol object
Args : a new group (optional)
Status : Public
This method works like group(), but only returns the group if it implements the start()
method. This is typical for similarity/assembly features, where the target encodes the
start and stop location of the alignment.
The returned object is of type Bio::DB::GFF::Homol, which is a subclass of
Bio::DB::GFF::Segment.
flatten_target
Title : flatten_target
Usage : $target = $f->flatten_target($f->target)
Function: flatten a target object
Returns : a string (GFF2), an array [GFF2.5] or an array ref [GFF3]
Args : a target object (required), GFF version (optional)
Status : Public
This method flattens a target object into text for GFF dumping. If a second argument is
provided, version-specific vocabulary is used for the flattened target.
hit
Title : hit
Usage : $hit = $f->hit([$new_hit])
Function: get or set the feature hit
Returns : a Bio::DB::GFF::Featname object
Args : a new group (optional)
Status : Public
This is the same as target(), for compatibility with Bio::SeqFeature::SimilarityPair.
id
Title : id
Usage : $id = $f->id
Function: get the feature ID
Returns : a database identifier
Args : none
Status : Public
This method retrieves the database identifier for the feature. It cannot be changed.
group_id
Title : group_id
Usage : $id = $f->group_id
Function: get the feature ID
Returns : a database identifier
Args : none
Status : Public
This method retrieves the database group identifier for the feature. It cannot be
changed. Often the group identifier is more useful than the feature identifier, since it
is used to refer to a complex object containing subparts.
clone
Title : clone
Usage : $feature = $f->clone
Function: make a copy of the feature
Returns : a new Bio::DB::GFF::Feature object
Args : none
Status : Public
This method returns a copy of the feature.
compound
Title : compound
Usage : $flag = $f->compound([$newflag])
Function: get or set the compound flag
Returns : a boolean
Args : a new flag (optional)
Status : Public
This method gets or sets a flag indicated that the feature is not a primary one from the
database, but the result of aggregation.
sub_SeqFeature
Title : sub_SeqFeature
Usage : @feat = $feature->sub_SeqFeature([$method])
Function: get subfeatures
Returns : a list of Bio::DB::GFF::Feature objects
Args : a feature method (optional)
Status : Public
This method returns a list of any subfeatures that belong to the main feature. For those
features that contain heterogeneous subfeatures, you can retrieve a subset of the
subfeatures by providing a method name to filter on.
This method may also be called as segments() or get_SeqFeatures().
add_subfeature
Title : add_subfeature
Usage : $feature->add_subfeature($feature)
Function: add a subfeature to the feature
Returns : nothing
Args : a Bio::DB::GFF::Feature object
Status : Public
This method adds a new subfeature to the object. It is used internally by aggregators,
but is available for public use as well.
attach_seq
Title : attach_seq
Usage : $sf->attach_seq($seq)
Function: Attaches a Bio::Seq object to this feature. This
Bio::Seq object is for the *entire* sequence: ie
from 1 to 10000
Example :
Returns : TRUE on success
Args : a Bio::PrimarySeqI compliant object
location
Title : location
Usage : my $location = $seqfeature->location()
Function: returns a location object suitable for identifying location
of feature on sequence or parent feature
Returns : Bio::LocationI object
Args : none
entire_seq
Title : entire_seq
Usage : $whole_seq = $sf->entire_seq()
Function: gives the entire sequence that this seqfeature is attached to
Example :
Returns : a Bio::PrimarySeqI compliant object, or undef if there is no
sequence attached
Args : none
merged_segments
Title : merged_segments
Usage : @segs = $feature->merged_segments([$method])
Function: get merged subfeatures
Returns : a list of Bio::DB::GFF::Feature objects
Args : a feature method (optional)
Status : Public
This method acts like sub_SeqFeature, except that it merges overlapping segments of the
same time into contiguous features. For those features that contain heterogeneous
subfeatures, you can retrieve a subset of the subfeatures by providing a method name to
filter on.
A side-effect of this method is that the features are returned in sorted order by their
start tposition.
sub_types
Title : sub_types
Usage : @methods = $feature->sub_types
Function: get methods of all sub-seqfeatures
Returns : a list of method names
Args : none
Status : Public
For those features that contain subfeatures, this method will return a unique list of
method names of those subfeatures, suitable for use with sub_SeqFeature().
attributes
Title : attributes
Usage : @attributes = $feature->attributes($name)
Function: get the "attributes" on a particular feature
Returns : an array of string
Args : feature ID
Status : public
Some GFF version 2 files use the groups column to store a series of attribute/value pairs.
In this interpretation of GFF, the first such pair is treated as the primary group for the
feature; subsequent pairs are treated as attributes. Two attributes have special meaning:
"Note" is for backward compatibility and is used for unstructured text remarks. "Alias"
is considered as a synonym for the feature name.
@gene_names = $feature->attributes('Gene');
@aliases = $feature->attributes('Alias');
If no name is provided, then attributes() returns a flattened hash, of attribute=>value
pairs. This lets you do:
%attributes = $db->attributes;
notes
Title : notes
Usage : @notes = $feature->notes
Function: get the "notes" on a particular feature
Returns : an array of string
Args : feature ID
Status : public
Some GFF version 2 files use the groups column to store various notes and remarks.
Adaptors can elect to store the notes in the database, or just ignore them. For those
adaptors that store the notes, the notes() method will return them as a list.
aliases
Title : aliases
Usage : @aliases = $feature->aliases
Function: get the "aliases" on a particular feature
Returns : an array of string
Args : feature ID
Status : public
This method will return a list of attributes of type 'Alias'.
Autogenerated Methods
Title : AUTOLOAD
Usage : @subfeat = $feature->Method
Function: Return subfeatures using autogenerated methods
Returns : a list of Bio::DB::GFF::Feature objects
Args : none
Status : Public
Any method that begins with an initial capital letter will be passed to AUTOLOAD and
treated as a call to sub_SeqFeature with the method name used as the method argument. For
instance, this call:
@exons = $feature->Exon;
is equivalent to this call:
@exons = $feature->sub_SeqFeature('exon');
SeqFeatureI methods
The following Bio::SeqFeatureI methods are implemented:
primary_tag(), source_tag(), all_tags(), has_tag(), each_tag_value() [renamed
get_tag_values()].
adjust_bounds
Title : adjust_bounds
Usage : $feature->adjust_bounds
Function: adjust the bounds of a feature
Returns : ($start,$stop,$strand)
Args : none
Status : Public
This method adjusts the boundaries of the feature to enclose all its subfeatures. It
returns the new start, stop and strand of the enclosing feature.
sort_features
Title : sort_features
Usage : $feature->sort_features
Function: sort features
Returns : nothing
Args : none
Status : Public
This method sorts subfeatures in ascending order by their start position. For reverse
strand features, it sorts subfeatures in descending order. After this is called
sub_SeqFeature will return the features in order.
This method is called internally by merged_segments().
asString
Title : asString
Usage : $string = $feature->asString
Function: return human-readabled representation of feature
Returns : a string
Args : none
Status : Public
This method returns a human-readable representation of the feature and is called by the
overloaded "" operator.
gff_string
Title : gff_string
Usage : $string = $feature->gff_string
Function: return GFF2 of GFF2.5 representation of feature
Returns : a string
Args : none
Status : Public
gff3_string
Title : gff3_string
Usage : $string = $feature->gff3_string([$recurse])
Function: return GFF3 representation of feature
Returns : a string
Args : An optional flag, which if true, will cause the feature to recurse over
subfeatures.
Status : Public
version
Title : version
Usage : $feature->version()
Function: get/set the GFF version to be returned by gff_string
Returns : the GFF version (default is 2)
Args : the GFF version (2, 2.5 of 3)
Status : Public
cmap_link()
Title : cmap_link
Usage : $link = $feature->cmap_link
Function: returns a URL link to the corresponding feature in cmap
Returns : a string
Args : none
Status : Public
If integrated cmap/gbrowse installation, it returns a link to the map otherwise it returns
a link to a feature search on the feature name. See the cmap documentation for more
information.
This function is intended primarily to be used in gbrowse conf files. For example:
link = sub {my $self = shift; return $self->cmap_viewer_link(data_source);}
A Note About Similarities
The current default aggregator for GFF "similarity" features creates a composite
Bio::DB::GFF::Feature object of type "gapped_alignment". The target() method for the
feature as a whole will return a RelSegment object that is as long as the extremes of the
similarity hit target, but will not necessarily be the same length as the query sequence.
The length of each "similarity" subfeature will be exactly the same length as its
target(). These subfeatures are essentially the HSPs of the match.
The following illustrates this:
@similarities = $segment->feature('similarity:BLASTN');
$sim = $similarities[0];
print $sim->type; # yields "gapped_similarity:BLASTN"
$query_length = $sim->length;
$target_length = $sim->target->length; # $query_length != $target_length
@matches = $sim->Similarity; # use autogenerated method
$query1_length = $matches[0]->length;
$target1_length = $matches[0]->target->length; # $query1_length == $target1_length
If you merge segments by calling merged_segments(), then the length of the query sequence
segments will no longer necessarily equal the length of the targets, because the alignment
information will have been lost. Nevertheless, the targets are adjusted so that the first
and last base pairs of the query match the first and last base pairs of the target.
BUGS
This module is still under development.
SEE ALSO
bioperl, Bio::DB::GFF, Bio::DB::RelSegment
AUTHOR
Lincoln Stein <lstein@cshl.org>.
Copyright (c) 2001 Cold Spring Harbor Laboratory.
This library is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.