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:
- •
- 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.
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.