TM::DM(3pm)						User Contributed Perl Documentation					       TM::DM(3pm)

NAME

       TM::DM - 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:

       o   only ONE identifier per item is supported

       o   at most ONE subject locator per topic is supported

       o   no variants are supported (might be added at some stage, poke me)

       o   a scope consists only of a single topic

       o   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.

SEE ALSO

       TM, TM::Easy

COPYRIGHT AND LICENSE

       Copyright 200[68] 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.

perl v5.10.1							    2008-05-07							       TM::DM(3pm)