NAME¶
TM::Index - Topic Maps, generic indexing support
SYNOPSIS¶
# this package only provides generic functionality
# see TM::Index::* for specific indices
DESCRIPTION¶
One performance bottleneck when using the TM package or any of its subclasses
are the low-level query functions "match_forall" and
"match_exists". They are looking for assertions of a certain nature.
Almost all high-level functions, and certainly TM::TS (TempleScript) use
these.
This package (actually more its subclasses) provides an indexing mechanism to
speed up the "match_*" functions by caching some results in a very
specific way. When an index is attached to a map, then it will intercept all
queries going to these functions.
Open vs. Closed Index¶
There are two options:
- "open":
- The default is to keep the index lazy. In this mode
the index is empty at the start and it will learn more and more on its
own. In this sense, the index lives under an open world assumption
(hence the name), as the absence of information does not mean that there
is no result.
- "closed":
- A closed world index has to be populated to be
useful. If a query is launched and the result is stored in the index, then
it will be used, like for an open index. If no result in the index is
found for a query, the empty result will be assumed.
Map Attachment¶
To activate an index, you have to attach it to a map. This is done at
constructor time.
It is possible (not sure how useful it is) to have one particular index to be
attached to several different maps. It is also possible to have several
TM::Index::* indices attached to one map. They are then consulted in the
sequence of attachments:
my $idx1 = new TM::Index::Whatever ($tm);
my $idx2 = new TM::Index::Whatever2 ($tm);
If $idx1 cannot help, then $idx2 is tried.
NOTE: If you use
several indices for the
same map, then all
of them
MUST be declared as being
open. If one of them were
closed, it would give a definite answer and would make the machinery not look
further into other indices. This implies that you will have to populate your
index explicitly.
Hash Technology¶
The default implementation uses an in-memory hash, no further fancy. Optionally,
you can provide your own hash object, also one which is
tied to an DBM
file, etc.
INTERFACE¶
Constructor¶
The only mandatory parameter for the constructor is the map for which this index
should apply. The map must be an instance of TM or any of its subclasses,
otherwise an exception is the consequence.
Optional parameters are
- "closed" (default: 0)
- This controls whether the index is operating under closed
or open world assumptions. If it is specified to be closed the
method "populate" will be triggered at the end of the
constructor.
- "cache" (default: "{}")
- You optionally can pass in your own HASH reference.
Example:
my $idx = new TM::Index::Match ($tm)
NOTE: When the index object goes out of scope, the destructor will make
the index detach itself from the map. Unfortunately, the exact moment when
this happens is somehow undefined in Perl, so it is better to do this manually
at the end.
Example:
{
my $idx2 = new TM::Index::Match ($tm, closed => 1);
....
} # destructor called and index detaches automatically, but only in theory
{
my $idx2 = new TM::Index::Match ($tm, closed => 1);
....
$idx2->detach; # better do things yourself
}
Methods¶
- attach
- $idx->attach
This method attaches the index to the configured map. Normally you will not
call this as the attachment is implicitly done at constructor time. The
index itself is not destroyed; it is just deactivated to be used together
with the map.
@@ optional TM
- detach
- $idx->detach
Makes the index detach safely from the map. The map is not harmed in this
process.
- discard
- $idx->discard
This throws away the index content.
- is_cached
- $bool =
$idx->is_cached ( $key)
Given a key parameter, the cache is consulted whether it already has a
result for this key. If the index is closed it will return the
empty list (reference), if it has no result, otherwise it will give back
"undef".
- do_cache
- $idx->do_cache
($key, $list_ref)
Given a key and a list reference, it will store the list reference there in
the cache.
SEE ALSO¶
TM, TM::Index::Characteristics, TM::Index::Match
COPYRIGHT AND LICENSE¶
Copyright 20(0[6]|10) 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.