man TM::DM (3): Topic Maps, read-only TMDM layer

SYNOPSIS

# somehow acquire a map (see TM and its subclasses)
my $tm = ....
# put a TMDM layer on top of it
use TM::DM;
my $tmdm = new TM::DM (map => $tm);
# get the TMDM topic map item
my $topicmap = $tmdm->topicmap;
# ask for all topics
my @topics = $topicmap->topics;
# for all associations
my @assocs = $topicmap->associations;
# get a particular topic
my $adam = $topicmap->topic ('adam');
# get some of its properties
$adam->id;
$adam->subjectLocators;
$adam->subjectIdentifiers;
$adam->parent;
my @ns = $adam->names;
my @os = $adam->occurrences;
# similar for assocs
my @as = $topicmap->associations (iplayer => 'adam');
$as[0]->type;
$as[0]->parent;
my @rs = $as[0]->roles;

ABSTRACT

This package provides a TMDM-ish (read-only) view on an existing topic map.

DESCRIPTION

TMDM, the Topic Maps Data Model

   http://www.isotopicmaps.org/sam/sam-model/

is the ISO standard for the high-level model for Topic Maps.

TMDM Concepts

TMDM's main concepts are the

topic map item: containing any number of topic and association items
topic item: containing any number of names, occurrence items, subject locators and subject identifiers
association item: containing a type, a scope and any number of role items
name item: containing a string, a type and a scope
occurrence item: containing a data value (together with its data type), a type and a scope
role item: containing a type and a player

All items have an item id and all (except the map) have a parent which links back to where the item belongs.

This package implements for each of the above a class and access methods to retrieve actual structure and values from an existing map. Nota bene, there are some deviations from TMDM:

only ONE identifier per item is supported
at most ONE subject locator per topic is supported
no variants are supported (might be added at some stage, poke me)
a scope consists only of a single topic
role items do not have an identity, so they also cannot be reified

Modus Operandi

Before you can use the TMDM layer, you need TM information in the form of a TM object. Any subclass should do, materialized and non-materialized maps should both be fine. Only with such a map you can instantiate a TMDM layer:

  use TM::Materialized::AsTMa;
  my $tm = new TM::Materialized::AsTMa (file => 'test.atm');
  use TM::DM;
  my $tmdm = new TM::DM (map => $tm);

Probably the first thing you need to do is to get a handle on the whole topic map:

  my $topicmap = $tmdm->topicmap;

That is delivered as an instance of TM::DM::TopicMap as described below. From there you start to extract topics and associations and that way you then further drill down.

Implementation Notes

This implementation only supports reading map information, not changing it or modifying the structure of the map. Not that it is impossible to do, but many applications get their map content from elsewhere and a read/write interface is an overkill in these cases.

All objects generated here are ephemeral, i.e. they are only instantiated because you wanted the map information embedded into them. This implies that if you ask for one and the same topic twice, you are getting two copies of the topic information. The following will not work as expected:

   my $t0 = $topicmap->topic ('adam');
   my $t1 = $topicmap->topic ('adam');
   warn "have the same topic!" if $t0 == $t1;

This will work:

   warn "have the same topic!" if $t0->id eq $t1->id;

INTERFACES

TM::DM

The TM::DM class itself does not offer much functionality itself. It only keeps the connection to the background map.

Constructor

The constructor expects exactly one parameter, namely the background map.

$tmdm = new TM::DM (map => $tm)

Methods

topicmap: $topicmap = $tmdm->topicmap
This method generates a Topic Map item. See TM::DM::TopicMap .

TM::DM::TopicMap

This class provides access to all TMDM properties:

id

This returns the item identifier.

topics

@topics = $topicmap->topics (@list-of-ids)

@topics = $topicmap->topics

@topics = $topicmap->topics ($selection-spec)

This method expects a list containing topic valid identifiers and returns for each of the topics a "TM::DM::Topic" reference. If any of the input identifiers do not denote a valid topic in the map, undef will be returned in its place. If the parameter list is empty, all topics will be returned. Have fun, I mean, use with care.

Examples:

    # round tripping topic ids
    print map { $_->id } $topicmap->topics ('abel', 'cain' );
    print "he again" if $topicmap->topics ('god');

If a selection is specified then the same language as in TM (method "toplets") can be used.

associations

@as = $topicmap->associations

@as = $topicmap->associations (%search_spec);

This method retrieves the list of ALL associations when it is invoked without a search specification. See TM for that.

reifier

This returns the topic item which reifies the association. "undef" is returned if there is none.

topic

This returns a topic item with that id. This method will die if the id is invalid. Note that always new copies are made.

TM::DM::Topic

subjectLocators: Returns the (only) subject locator (URI string) in the topic item or "undef" if there is none.
subjectIdentifiers: Returns a list of URI strings. Might be empty.
id: Returns the item id.
parent: Returns a TM::DM::TopicMap item in which this topic is embedded.
names: @names = $topic->names
Returns a list of TMDM name items.
occurrences: @occurrences = $topic->occurrences
Returns a list of TMDM occurrences items.
roles: @roles = $topic->roles
Returns a list of TM::DM::Role items where this topic plays any role.

TM::DM::Association

id: Returns the item id.
type: Returns a TM::DM::Topic item which is the type of the association. This is always defined.
scope: Returns the scope of the association in the form of a single TM::DM::Topic item. This is always defined as for the unconstrained scope the topic "us" is used (see TM::PSI).
roles: @roles = $assoc->roles
Returns a list of roles of the association. Each role is a TM::DM::Role item.
parent: Returns a TM::DM::TopicMap item for the embedding map.
reifier: Returns a TM::DM::Topic item if this association is reified. "undef" otherwise.

TM::DM::Occurrence

id: Returns the item id.
value: Returns the value (together with the data type) in the form of a TM::Literal object.
type: Returns a TM::DM::Topic item which is the type of the occurrence. This is always defined.
scope: Returns the scope of the occurrence in the form of a single TM::DM::Topic item. This is always defined.
reifier: Returns a TM::DM::Topic item if this occurrence is reified. "undef" otherwise.
parent: Returns the TM::DM::Topic item of the topic where this occurrence is part of.

TM::DM::Name

id: Returns the item id.
value: Returns the string value of the name.
type: Returns a TM::DM::Topic item which is the type of the name. This is always defined.
scope: Returns the scope of the name in the form of a single TM::DM::Topic item. This is always defined.
reifier: Returns a TM::DM::Topic item if this name is reified. "undef" otherwise.
parent: Returns the TM::DM::Topic item of the topic where this name is part of.

TM::DM::Role

player: Returns a TM::DM::Topic item for the topic which is the player in this role.
type: Returns a TM::DM::Topic item for the topic which is the type of this role.
parent: Returns a TM::DM::Association item of the association where this role is in.

COPYRIGHT AND LICENSE

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.