TM::Graph - Topic Maps, trait for graph-like operations
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NAME
TM::Graph - Topic Maps, trait for graph-like operations
SYNOPSIS
use TM::Materialized::AsTMa;
my $tm = new TM::Materialized::AsTMa (file => 'old_testament.atm');
$tm->sync_in;
Class::Trait->apply ( $tm => 'TM::Graph' );
# find groups of topics connected
print Dumper $tm->clusters;
# use association types to compute a hull
print "friends of Mr. Cairo: ".
Dumper [
$tm->frontier ([ $tm_>tid ('mr-cairo') ], [ [ $tm->tids ('foaf') ] ])
];
# see whether there is a link (direct
print "I always knew it"
if $tm->is_path ( [ 'gw-bush' ], # there could be more
(bless [ [ 'foaf' ] ], '*'),
'osama-bin-laden');
DESCRIPTION
Obviously a topic map is also a graph, the topics being the nodes, and the associations forming the
edges, albeit these connections connect not always only two nodes, but, ok, you should know TMs by now.
This package provides some functions which focus more on the graph-like nature of Topic Maps.
INTERFACE
Methods
This trait provides the following methods:
- clusters
-
$hashref = clusters ($tm)
computes the islands of topics. It figures out which topics are connected via associations and - in case they are -
will collate them into clusters. The result is a hash reference to a hash containing list references of topic ids
organized in a cluster.
In default mode, this function only regards topics to be in the same cluster if topics play roles in one and the same
maplet. The role topics themselves or the type or the scope are ignored.
You can change this behaviour by passing in options like
use_scope => 1
use_roles => 1
use_type => 1
Obviously, with use_scope => 1 you will let a lot of topics collapse into one cluster as most maplets usually are
in the unconstrained scope.
NOTE: This is yet a somewhat expensive operation.
- frontier
-
@hull = $tm->frontier (\@start_lids, $path_spec)
This method computes a qualified hull, i.e. a list of all topics which are reachable from
@start_lids via a path specified by $path_spec. The path specification is a (recursive) data
structure, describing sequences, alternatives and repetition (the * operator), all encoded as
lists of lists. The topics in that path specification are interpreted as assertion types.
Example (reformatting for better reading):
# a single step: start knows ...
[ ] # outer level: sequence (there is only one)
[ 'knows' ] # inner level: alternatives (there is only one)
# two subsequent steps: start knows ... isa ...
[ ] # outer level: two entries
[ 'knows' ], [ 'isa' ] # inner level, one entry each
# repetition: start knows ... knows ... knows ... ad infinitum
bless [ ], '*' # outer level: one entry, but blessed
[ 'knows' ] # inner level
# alternatives: start knows | hates ...
[ ] # outer level: one entry
[ 'knows', 'hates' ] # inner level: alternatives
# nesting: first follow an 'eats', then any number of 'begets'
[ ]
[ 'eats' ], [ ]
bless [ ], '*'
[ 'begets' ]
NOTE: All tids have to be made map-absolute with tids.
NOTE: Cycles are detected.
NOTE: I am not sure how this performs at rather large graphs, uhm, maps.
- is_path
-
$bool = $tm->is_path (\@start_lids, $path_spec, $end_lid)
This method returns 1 if there is a path from start_lids to end_lid via the path
specification. See frontier for that one.
- neighborhood
-
@neighbors = $tm->neighborhood ($MAXDEPTH, \@start_lids)
This method returns a list of neighbors for the given start LIDs. In that it follows paths with the
maximal length given as first parameter. In any case the path with length 0 is returned, which
includes any of the starting nodes.
Each neighbor is represented by a hash (reference) with the path and the end LID. The path
is a list (reference) holding the LIDs of the association types visited along the path.
SEE ALSO
COPYRIGHT AND LICENSE
Copyright 200[78] by Robert Barta, <drrho@cpan.org>
This library is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
package TM::Graph;
use strict;
use Data::Dumper;
use TM;
use Class::Trait 'base';
sub clusters {
my $tm = shift;
my %opts = @_;
# by default
# not using scope
# not using type
# not using roles
$opts{use_lid} = 1 unless defined $opts{use_lid}; # always use maplet ID
my $i = 0;
my $clusters = { map { $_ => $i++ } map { $_->[TM->LID] } $tm->toplets }; # we store every toplet into its own cluster
foreach my $m ($tm->match (TM->FORALL, nochar => 1)) {
my @candidates;
# push @candidates, $m->[TM->LID] if $opts{use_lid};
push @candidates, $m->[TM->TYPE] if $opts{use_type};
push @candidates, $m->[TM->SCOPE] if $opts{use_scope};
push @candidates, @ { $m->[TM->ROLES] } if $opts{use_roles};
push @candidates, @ { $m->[TM->PLAYERS] };
my $i = $clusters->{shift @candidates};
foreach (@candidates) {
my $j = $clusters->{$_};
# now all entries which have currently $j must be turned into $i
unless ($i == $j) {
map { $clusters->{$_} = $clusters->{$_} == $j ? $i : $clusters->{$_} } keys %{$clusters};
}
}
}
my @clusters = map { [] } values %$clusters;
map { push @{@clusters[ $clusters->{$_} ]}, $_ } keys %$clusters ;
return [ grep (@$_, @clusters)]; # get rid of empty clusters
}
sub frontier {
my $tm = shift;
my $as = shift;
my $ps = shift;
my @bs = _frontier_star ($tm, $as, {}, $ps); # {} are the axes followed so far
sub _frontier_star {
my $tm = shift;
my $as = shift; # the list (ref) of things where we are now
my $vs = shift; # what have we visited so far, hash ref
my $ps = shift; # a list ref for the sequence of path items left to be done
if (ref ($ps) eq '*') { # if *'ed then add the starting points
my @front = @$as; # start off with the starting points, they belong to it
while (1) { # repeat ad-infinitum
my @bs = _frontier_seq ($tm, \@front, $vs, $ps) ; # compute from the current front
last unless @bs; # there might not be any new ($vs has side effects!!!!!!!!)
push @front, @bs; # what we got we collect
{ my %X; map { $X{$_}++ } @front; @front = keys %X; } # make that unique (otherwise too many identical entries)
}
return @front; # and finally return it
} else {
return _frontier_seq ($tm, $as, $vs, $ps)
}
}
sub _frontier_seq {
my $tm = shift;
my $as = shift; # the list (ref) of things where we are now
my $vs = shift; # what have we visited so far, hash ref
my $ps = shift; # a list ref for the sequence of path items left to be done
my $front = $as;
foreach my $p (@$ps) { # one step after the other
$front = [ _frontier_alt ($tm, $front, $vs, $p) ]; # compute what we can reach from there
{ my %X; map { $X{$_}++ } @$front; $front = [ keys %X ]; } # make that unique (otherwise too many identical entries)
}
return @$front;
}
sub _frontier_alt {
my $tm = shift;
my $as = shift;
my $vs = shift; # what have we visited so far, hash ref
my $os = shift; # a list of alternative paths
my @front;
foreach my $o (@$os) {
push @front, _frontier_step ($tm, $as, $vs, $o);
}
{ my %X; map { $X{$_}++ } @front; @front = keys %X; }; # make that unique (otherwise too many identical entries)
return @front;
}
sub _frontier_step {
my $tm = shift;
my $as = shift;
my $vs = shift; # what have we visited so far, hash ref
my $s = shift; # the step
if (ref ($s) eq '*') { # something more complex, can only be sequence
return _frontier_star ($tm, $as, $vs, $s);
} elsif (ref ($s)) { # something more complex, can only be sequence
return _frontier_seq ($tm, $as, $vs, $s);
} else { # atomic step
my @as = grep { $vs->{$_}->{$s}++ == 0 } @$as; # get rid of those where we already followed that axis
if ($s eq 'isa') { # instance of, easy
return map { $tm->typesT ($_) } @as; # compute their types
} elsif ($s eq 'iko') { # subclasses, easy
return map { $tm->superclassesT ($_) } @as; # computer their superclasses
} else {
my $tt = $tm->mids ($s);
return
map { $tm->get_players ($_) }
map { $tm->match_forall (type => $tt, iplayer => $_) }
@as;
}
}
}
}
sub is_path {
my $tm = shift;
my $as = shift;
my $ps = shift;
my $b = shift;
my $bt = $tm->mids ($b) or $TM::log->logdie ("end topic not in map");
return grep { $_ eq $bt } $tm->frontier ( [ $tm->mids (@$as) ], $ps);
}
sub neighborhood {
my $self = shift;
my $DEPTH = shift;
my $starts = shift;
my @starts = grep { $_ } $self->mids (@$starts); # make sure we only have defined ones
my @ns = map { { path => [], end => $_ } } @starts; # bootstrap result, will be accumulated below
return _neighborhood ($self,
\@ns, # current paths and frontiers
$DEPTH, 1, # max depth and current depth
);
sub _neighborhood {
my $self = shift;
my $ns = shift;
my $DEPTH = shift;
my $depth = shift;
if ($depth > $DEPTH) { # if we went too far
return @$ns; # this is the result
} else { # still not at DEPTH
my %seen = map { $_ => 1 } # build already seen hash
map { $_->{end} } # find end points
@$ns; # walk through all paths we have
my @ns;
foreach my $n (@$ns) {
my @as = $self->match_forall (iplayer => $n->{end});
foreach my $a (@as) {
push @ns,
map { # construct path/end combo
{ path => [ @{$n->{path}}, $a->[TM->TYPE] ],
end => $_
}
}
grep { !$seen{ $_ }++ } # filter out those which we have already (and mark them seen)
$self->get_players ($a); # get all players of this assoc
}
}
return _neighborhood ($self, # the map
[ @ns, @$ns ],
$DEPTH, $depth+1, # max depth and current depth
);
}
}
}
our $VERSION = 0.3;
our $REVISION = '$Id: Graph.pm,v 1.1 2007/07/28 16:40:31 rho Exp $';
1;
__END__
sub _is_path {
my $tm = shift;
my $a = shift;
my $b = shift;
my $vs = shift; # what have we visited so far
# @_ contains a sequence of steps
return $a eq $b if scalar @_ == 0; # empty path? then a == b
# ok, there is more of a path
$vs->{$a} = 1; # make an entry in the visitor's guestbook
my $r = shift; # take the first step
# or list
foreach my $s (@$r) { # this is a list of or'ed steps, s is an atom (= list reference, possibly blessed, contains only ONE element)
my $t = $s->[0];
if (ref ($s) eq '*') {
die;
} else {
my @bs = _make_step ($tm, $vs, $tm->mids ($t), $a);
return grep { $b eq $_ } @bs unless @_; # if there is more, we have to continue, otherwise, all if a == b
foreach my $b2 (@bs) {
return 1 if _is_path ($tm, $b2, $b, $vs, @_);
}
return 0;
}
if (! ref ($r)) { # something simple, one id
if ($r =~ /(\w+)\*$/) { # this is a repetition*
my $t2 = $tm->mids ($1);
return 1 if _is_path ($tm, $a, $b, $vs, @_); # empty step is also ok
my @bs = _make_step ($tm, $vs, $t2, $a); # get the next in the front
foreach my $b2 (@bs) {
return 1 if _is_path ($tm, $b2, $b, $vs, ($r, @_)); # use the original expression
}
return 0;
} else { # one single step from $a via $r
}
} else { # an OR
die;
}
}
xxx=cut
computes a tree of topics based on a starting topic, an association type
and two roles. Whenever an association of the given type is found and the given topic appears in the
role given in this very association, then all topics appearing in the other given role are regarded to be
children in the result tree. There is also an optional C<depth> parameter. If it is not defined, no limit
applies. Starting from XTM::base version 0.34 loops are detected and are handled gracefully. The returned
tree might contain loops then.
Examples:
$hierarchy = $tm->induced_assoc_tree (topic => $start_node,
assoc_type => 'at-relation',
a_role => 'tt-parent',
b_role => 'tt-child' );
$yhcrareih = $tm->induced_assoc_tree (topic => $start_node,
assoc_type => 'at-relation',
b_role => 'tt-parent',
a_role => 'tt-child',
depth => 42 );
B<Note>
x=cut
x=pod