NAME¶
TM::MapSphere - Topic Maps, trait for a hierarchical TM repository
SYNOPSIS¶
# construct an adhoc-ish map sphere
use TM;
my $tm = new TM; # create a map
use Class::Trait;
Class::Trait->apply ($tm, 'TM::MapSphere'); # make it a sphere
$tm->mount ('/abc/' => new TM); # mount a map into location /abc/
# this creates a topic in the map with a reference to another (empty) map
# any subclass of TM can used
$tm->mount ('/def/' => new TM::Materialized::AsTMa (file => 'test.atm'));
# check a mount point
warn "damn" unless $tm->is_mounted ('/xxx/');
# do some sync stuff on any resource-connected map
$tm->is_mounted ('/def/')->sync_in;
# get rid of some mount point
$tm->umount ('/abc/');
$tm->internalize ('aaa'); # it is a map, so all map methods work
print $tm->mids ('def'); # this topic exists and should be a map
# find all child maps
@maps = $tm->instances (\ TM::PSI->TOPICMAP);
DESCRIPTION¶
This package provides a
mapspheric trait, i.e. all functionality to
convert any map into a (hierarchical) Topic Maps database. The basic idea is
that one map (the
root) contains not only arbitrary map data, but can
also contain references to other maps. On the top level, addressed as
"/" is then the root map. The child maps have addresses such as
"/abc/" and "/internet/web/browsers/". The idea is also
that a map can contain other maps, simply by having topics which stand for
these child maps. In that sense, a map is always a tree of maps (hence
MapSphere).
These trees are not necessarily static. At any point, a new map can be hooked
in, or removed. This process is quite similar to
mounting devices into
a UNIX file system.
Each of the referenced child maps is represented as a topic of a predefined type
"TM::PSI::TOPICMAP", the subject indicator is interpreted as the URL
to the resources for these maps.
The root map can be any subclass of TM. You can therefore choose to have only a
shortlived mapsphere which will be lost on process termination, or
alternatively, to take one of the persistent storages. Also, the individual
child maps can be of different provenances. Any subclass of TM will do,
consequently also any which have the trait of TM::ResourceAble or
TM::Synchronizable. This implies that this database can be heterogenuous, in
that different maps can be stored differently, or can even be kept remotely.
Once you have your map sphere, you can write it out via synchronization with the
external resources. You can do this for the whole sphere, or for a particular
subtree of maps. Conversely, you can read in the whole map sphere by starting
with the root and letting the system to recursively bootstrap the whole
sphere.
Tau Objects¶
Map spheres can only store
Tau objects. At the moment, these are only
maps. See TM::PSI for predefined things.
Namespace¶
To address a particular object in a repository we follow a convention similar to
file system paths: Every object has a path like
/something/complete/else/
Note, that all paths for maps should start and end with a "/", so that
maps can be seen as
directories. All other objects (constraints,
queries, ...) are represented as topics.
The namespace cannot have
holes, so that the following will result in an
error:
$tm->mount ('/something/', ...);
$tm->mount ('/something/completely/else/', ....); # we will die here
Since a map sphere behaves like a map, any meta data about child maps should be
modelled according to the TM paradigm.
INTERFACE¶
This interface allows to
mount and
unmount other maps into
another.
Methods¶
- mount
- $tm->mount ($path =>
$tm2, [ $force ])
This mounts a map $tm2 into the map sphere at the given path. Only maps can
be mounted, everything else results in an error. The root will be always
mounted to the map sphere itself. It is an error to try to change this.
If the mount point is already taken, an exception will be raised. This can
be suppressed when the "force" parameter is set:
$tm->mount ('/xyz/' => $child, 1);
A topic of type "topicmap" (see TM::PSI) is created in the map
above the mount point. The base URI of the map is used as subject address.
If the mounted map has a resource URL that is used as subject indicator
(identifier in TMDM-speak). Additionally, the topic gets asserted
characteristics:
Maps can only be mounted into other maps if these already are also mounted. The
following code will not work:
my $tm = new SomeMapSphere;
$tm->mount ('/abc/def/' => ....); # die here because there is no map mounted to /abc/ yet
- umount
- $tm->umount ($path)
This unmounts a map from the object map. Obviously, the path must point to
an existing topic of type "topicmap". All maps beyond this mount
point are removed, i.e. also all children will go down the drain.
The root cannot be unmounted.
- is_mounted
- $child = $tm->is_mounted
( $path)
Simply returns a map object mounted on that given mount point.
"undef" if there is none.
- mounttab
- %mt = %{ $tm->mounttab }
$tm->mounttab ( \ $%mt )
This accessor sets/gets the mount table.
Note: You will hardly need access directly to it, normally, and
changing it in an uncontrolled way may corrupt the whole data structure.
The reason it exists, though, is that sometimes you have to
indicate that there is a change, such as when using this together with
MLDBM.
This, for example, does NOT work:
{
my $tm = new ...MapSphericalClassUsingMLDBM...;
...
$tm->is_mounted ('/whatever/')->sync_in;
# A: now the child is happily sync'ed in
# but MLDBM did not realize it, so it is not written back into the
# underlying file
}
{
# regain the MLDBM based MapSphere later
my $tm = new ...MapSphericalClassUsingMLDBM...;
# child is not sync'ed in as under A: above
}
This does work:
{
my $tm = new ...MapSphericalClassUsingMLDBM...;
...
my $mt = $tm->mounttab;
$tm->is_mounted ('/whatever/')->sync_in;
$tm->mounttab ($mt);
# now the changes will be written onto the MLDBM file
}
Of course, more thought can be spent on how much actually has to be
written back. Above approach may be wasteful.
AUTHOR¶
Robert Barta, <drrho@cpan.org>
COPYRIGHT AND LICENSE¶
Copyright (C) 200[4-7] by Robert Barta
This library is free software; you can redistribute it and/or modify it under
the same terms as Perl itself, either Perl version 5.8.4 or, at your option,
any later version of Perl 5 you may have available.