1Algorithm::Dependency(3U)ser Contributed Perl DocumentatiAolngorithm::Dependency(3)
2
6 Algorithm::Dependency - Base class for implementing various dependency
7 trees
8
10 use Algorithm::Dependency;
11 use Algorithm::Dependency::Source::File;
12 # Load the data from a simple text file
14 my $data_source = Algorithm::Dependency::Source::File->new( 'foo.txt' );
15 # Create the dependency object, and indicate the items that are already
17 # selected/installed/etc in the database
18 my $dep = Algorithm::Dependency->new(
19 source => $data_source,
20 selected => [ 'This', 'That' ]
21 ) or die 'Failed to set up dependency algorithm';
22 # For the item 'Foo', find out the other things we also have to select.
24 # This WON'T include the item we selected, 'Foo'.
25 my $also = $dep->depends( 'Foo' );
26 print $also
27 ? "By selecting 'Foo', you are also selecting the following items: "
28 . join( ', ', @$also )
29 : "Nothing else to select for 'Foo'";
30 # Find out the order we need to act on the items in.
32 # This WILL include the item we selected, 'Foo'.
33 my $schedule = $dep->schedule( 'Foo' );
34
36 Algorithm::Dependency is a framework for creating simple read-only
37 dependency heirachies, where you have a set of items that rely on other
38 items in the set, and require actions on them as well.
39 Despite the most visible of these being software installation systems
41 like the CPAN installer, or debian apt-get, they are usefull in other
42 situations. This module intentionally uses implementation-neutral
43 words, to avoid confusion.
44 Terminology
46 The term "ITEM" refers to a single entity, such as a single software
47 package, in the overall set of possible entities. Internally, this is a
48 fairly simple object. See Algorithm::Dependency::Item for details.
49 The term "SELECT" means that a particular item, for your purposes, has
51 already been acted up in the required way. For example, if the software
52 package had already been installed, and didn't need to be re-installed,
53 it would be "SELECTED".
54 The term "SOURCE" refers to a location that contains the master set of
56 items. This will be very application specific, and might be a flat
57 file, some form of database, the list of files in a folder, or
58 generated dynamically.
59 General Description
61 Algorithm::Dependency implements algorithms relating to dependency
62 heirachies. To use this framework, all you need is a source for the
63 master list of all the items, and a list of those already selected. If
64 your dependency heirachy doesn't require the concept of items that are
65 already selected, simply don't pass anything to the constructor for it.
66 Please note that the class Algorithm::Dependency does NOT implement an
68 ordering, for speed and simplicity reasons. That is, the "schedule" it
69 provides is not in any particular order. If item 'A' depends on item
70 'B', it will not place B before A in the schedule. This makes it
71 unsuitable for things like software installers, as they typically would
72 need B to be installed before A, or the installation of A would fail.
73 For dependency heirachies requiring the items to be acted on in a
75 particular order, either top down or bottom up, see
76 Algorithm::Dependency::Ordered. It should be more applicable for your
77 needs. This is the the subclass you would probably use to implement a
78 simple ( non-versioned ) package installation system. Please note that
79 an ordered heirachy has additional constraints. For example, circular
80 dependencies ARE legal in a non-ordered heirachy, but ARE NOT legal in
81 an ordered heirachy.
82 Extending
84 A module for creating a source from a simple flat file is included. For
85 details see Algorithm::Dependency::Source::File. Information on
86 creating a source for your particular use is in
87 Algorithm::Dependency::Source.
88
90 new %args
91 The constructor creates a new context object for the dependency
92 algorithms to act in. It takes as argument a series of options for
93 creating the object.
94 source => $Source
96 The only compulsory option is the source of the dependency items.
97 This is an object of a subclass of Algorithm::Dependency::Source.
98 In practical terms, this means you will create the source object
99 before creating the Algorithm::Dependency object.
100 selected => [ 'A', 'B', 'C', etc... ]
102 The "selected" option provides a list of those items that have
103 already been 'selected', acted upon, installed, or whatever. If
104 another item depends on one in this list, we don't have to include
105 it in the output of the "schedule" or "depends" methods.
106 ignore_orphans => 1
108 Normally, the item source is expected to be largely perfect and
109 error free. An 'orphan' is an item name that appears as a
110 dependency of another item, but doesn't exist, or has been deleted.
111 By providing the "ignore_orphans" flag, orphans are simply ignored.
113 Without the "ignore_orphans" flag, an error will be returned if an
114 orphan is found.
115 The "new" constructor returns a new Algorithm::Dependency object on
117 success, or "undef" on error.
118 source
120 The "source" method retrieves the Algorithm::Dependency::Source object
121 for the algorithm context.
122 selected_list
124 The "selected_list" method returns, as a list and in alphabetical
125 order, the list of the names of the selected items.
126 selected $name
128 Given an item name, the "selected" method will return true if the item
129 is selected, false is not, or "undef" if the item does not exist, or an
130 error occurs.
131 item $name
133 The "item" method fetches and returns the item object, as specified by
134 the name argument.
135 Returns an Algorithm::Dependency::Item object on success, or "undef" if
137 an item does not exist for the argument provided.
138 depends $name1, ..., $nameN
140 Given a list of one or more item names, the "depends" method will
141 return a reference to an array containing a list of the names of all
142 the OTHER items that also have to be selected to meet dependencies.
143 That is, if item A depends on B and C then the "depends" method would
145 return a reference to an array with B and C. ( "[ 'B', 'C' ]" )
146 If multiple item names are provided, the same applies. The list
148 returned will not contain duplicates.
149 The method returns a reference to an array of item names on success, a
151 reference to an empty array if no other items are needed, or "undef" on
152 error.
153 schedule $name1, ..., $nameN
155 Given a list of one or more item names, the "depends" method will
156 return, as a reference to an array, the ordered list of items you
157 should act upon.
158 This would be the original names provided, plus those added to satisfy
160 dependencies, in the prefered order of action. For the normal
161 algorithm, where order it not important, this is alphabetical order.
162 This makes it easier for someone watching a program operate on the
163 items to determine how far you are through the task and makes any logs
164 easier to read.
165 If any of the names you provided in the arguments is already selected,
167 it will not be included in the list.
168 The method returns a reference to an array of item names on success, a
170 reference to an empty array if no items need to be acted upon, or
171 "undef" on error.
172 schedule_all;
174 The "schedule_all" method acts the same as the "schedule" method, but
175 returns a schedule that selected all the so-far unselected items.
176
178 Add the "check_source" method, to verify the integrity of the source.
179 Possibly add Algorithm::Dependency::Versions, to implement an ordered
181 dependency tree with versions, like for perl modules.
182 Currently readonly. Make the whole thing writable, so the module can be
184 used as the core of an actual dependency application, as opposed to
185 just being a tool.
186
188 Bugs should be submitted via the CPAN bug tracker, located at
189 http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Algorithm-Dependency
191 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Algorithm-Dependency>
192 For general comments, contact the author.
194
196 Adam Kennedy <adamk@cpan.org>
197
199 Algorithm::Dependency::Ordered, Algorithm::Dependency::Item,
200 Algorithm::Dependency::Source, Algorithm::Dependency::Source::File
201
203 Copyright 2003 - 2009 Adam Kennedy.
204 This program is free software; you can redistribute it and/or modify it
206 under the same terms as Perl itself.
207 The full text of the license can be found in the LICENSE file included
209 with this module.
210perl v5.12.0 2009-04-14 Algorithm::Dependency(3)