Manual Reference Pages - ALGORITHM::DEPENDENCY (3)
Algorithm::Dependency - Base class for implementing various dependency trees
# Load the data from a simple text file
my $data_source = Algorithm::Dependency::Source::File->new( foo.txt );
# Create the dependency object, and indicate the items that are already
# selected/installed/etc in the database
my $dep = Algorithm::Dependency->new(
source => $data_source,
selected => [ This, That ]
) or die Failed to set up dependency algorithm;
# For the item Foo, find out the other things we also have to select.
# This WONT include the item we selected, Foo.
my $also = $dep->depends( Foo );
? "By selecting Foo, you are also selecting the following items: "
. join( , , @$also )
: "Nothing else to select for Foo";
# Find out the order we need to act on the items in.
# This WILL include the item we selected, Foo.
my $schedule = $dep->schedule( Foo );
Algorithm::Dependency is a framework for creating simple read-only
dependency heirachies, where you have a set of items that rely on other
items in the set, and require actions on them as well.
Despite the most visible of these being software installation systems like
the CPAN installer, or debian apt-get, they are usefull in other situations.
This module intentionally uses implementation-neutral words, to avoid
The term ITEM refers to a single entity, such as a single software
package, in the overall set of possible entities. Internally, this is a
fairly simple object. See Algorithm::Dependency::Item for details.
The term SELECT means that a particular item, for your purposes, has
already been acted up in the required way. For example, if the software
package had already been installed, and didnt need to be re-installed,
it would be SELECTED.
The term SOURCE refers to a location that contains the master set of
items. This will be very application specific, and might be a flat file,
some form of database, the list of files in a folder, or generated
Algorithm::Dependency implements algorithms relating to dependency
heirachies. To use this framework, all you need is a source for the master
list of all the items, and a list of those already selected. If your
dependency heirachy doesnt require the concept of items that are already
selected, simply dont pass anything to the constructor for it.
Please note that the class Algorithm::Dependency does NOT implement an
ordering, for speed and simplicity reasons. That is, the schedule it
provides is not in any particular order. If item A depends on item B,
it will not place B before A in the schedule. This makes it unsuitable for
things like software installers, as they typically would need B to be
installed before A, or the installation of A would fail.
For dependency heirachies requiring the items to be acted on in a particular
order, either top down or bottom up, see Algorithm::Dependency::Ordered.
It should be more applicable for your needs. This is the the subclass you
would probably use to implement a simple ( non-versioned ) package
installation system. Please note that an ordered heirachy has additional
constraints. For example, circular dependencies ARE legal in a
non-ordered heirachy, but ARE NOT legal in an ordered heirachy.
A module for creating a source from a simple flat file is included. For
details see Algorithm::Dependency::Source::File. Information on creating
a source for your particular use is in Algorithm::Dependency::Source.
The constructor creates a new context object for the dependency algorithms to
act in. It takes as argument a series of options for creating the object.
The new constructor returns a new Algorithm::Dependency object on success,
or undef on error.
source => $Source
The only compulsory option is the source of the dependency items. This is
an object of a subclass of Algorithm::Dependency::Source. In practical terms,
this means you will create the source object before creating the
selected => [ A, B, C, etc... ]
The selected option provides a list of those items that have already been
selected, acted upon, installed, or whatever. If another item depends on one
in this list, we dont have to include it in the output of the schedule or
ignore_orphans => 1
Normally, the item source is expected to be largely perfect and error free.
An orphan is an item name that appears as a dependency of another item, but
doesnt exist, or has been deleted.
By providing the ignore_orphans flag, orphans are simply ignored. Without
the ignore_orphans flag, an error will be returned if an orphan is found.
The source method retrieves the Algorithm::Dependency::Source object
for the algorithm context.
The selected_list method returns, as a list and in alphabetical order,
the list of the names of the selected items.
Given an item name, the selected method will return true if the item is
selected, false is not, or undef if the item does not exist, or an error
The item method fetches and returns the item object, as specified by the
Returns an Algorithm::Dependency::Item object on success, or undef if
an item does not exist for the argument provided.
depends CW$name1, ..., CW$nameN
Given a list of one or more item names, the depends method will return
a reference to an array containing a list of the names of all the OTHER
items that also have to be selected to meet dependencies.
That is, if item A depends on B and C then the depends method would
return a reference to an array with B and C. ( [ B, C ] )
If multiple item names are provided, the same applies. The list returned
will not contain duplicates.
The method returns a reference to an array of item names on success, a
reference to an empty array if no other items are needed, or undef
schedule CW$name1, ..., CW$nameN
Given a list of one or more item names, the depends method will return,
as a reference to an array, the ordered list of items you should act upon.
This would be the original names provided, plus those added to satisfy
dependencies, in the prefered order of action. For the normal algorithm,
where order it not important, this is alphabetical order. This makes it
easier for someone watching a program operate on the items to determine
how far you are through the task and makes any logs easier to read.
If any of the names you provided in the arguments is already selected, it
will not be included in the list.
The method returns a reference to an array of item names on success, a
reference to an empty array if no items need to be acted upon, or undef
The schedule_all method acts the same as the schedule method, but
returns a schedule that selected all the so-far unselected items.
Add the check_source method, to verify the integrity of the source.
Possibly add Algorithm::Dependency::Versions, to implement an ordered
dependency tree with versions, like for perl modules.
Currently readonly. Make the whole thing writable, so the module can be
used as the core of an actual dependency application, as opposed to just
being a tool.
Bugs should be submitted via the CPAN bug tracker, located at
For general comments, contact the author.
Adam Kennedy <email@example.com>
Copyright 2003 - 2009 Adam Kennedy.
This program is free software; you can redistribute
it and/or modify it under the same terms as Perl itself.
The full text of the license can be found in the
LICENSE file included with this module.
|perl v5.20.3 ||ALGORITHM::DEPENDENCY (3) ||2009-04-14 |
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