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README for Tree::DAG_Node

Tree::DAG_Node
			     version 1.06

[Partially excerpted from the POD.]

Tree::DAG_Node is a (super)class for representing nodes in a tree.

This class encapsulates/makes/manipulates objects that represent nodes
in a tree structure.  The tree structure is not an object itself, but
is emergent from the linkages you create between nodes.  This class
provides the methods for making linkages that can be used to build up
a tree, while preventing you from ever making any kinds of linkages
which are not allowed in a tree (such as having a node be its own
mother or ancestor, or having a node have two mothers).

This is what I mean by a "tree structure", a bit redundantly stated:

* A tree is a special case of an acyclic directed graph.

* A tree is a network of nodes where there's exactly one root node
    (i.e., 'the top'), and the only primary relationship between nodes
    is the mother-daughter relationship.

* No node can be its own mother, or its mother's mother, etc.

* Each node in the tree has exactly one "parent" (node in the "up"
    direction) -- except the root, which is parentless.

* Each node can have any number (0 to any finite number) of
    daughter nodes. A given node's daughter nodes constitute an
    *ordered* list.  (However, you are free to consider this ordering
    irrelevant. Some applications do need daughters to be ordered, so
    I chose to consider this the general case.)

* A node can appear in only one tree, and only once in that tree.
    Notably (notable because it doesn't follow from the two above
    points), a node cannot appear twice in its mother's daughter list.

* In other words, there's an idea of up (toward the root) versus
    down (away from the root), and left (i.e., toward the start (index
    0) of a given node's daughter list) versus right (toward the end
    of a given node's daughter list).

Trees as described above have various applications, among them:
representing syntactic constituency, in formal linguistics;
representing contingencies in a game tree; representing abstract
syntax in the parsing of any computer language -- whether in
expression trees for programming languages, or constituency in the
parse of a markup language document.  (Some of these might not use the
fact that daughters are ordered.)

Note: B-Trees are a very special case of the above kinds of trees, and
are best treated with their own class.  Check CPAN for modules
encapsulating B-Trees; or if you actually want a database, and for
some reason ended up looking here, go look at the AnyDBM_File
manpage.)

Many base classes are not usable except as such -- but Tree::DAG_Node
can be used as a normal class.

PREREQUISITES

This suite requires Perl 5; I've only used it under Perl 5.004, so for
anything lower, you're on your own.

Tree::DAG_Node doesn't use any nonstandard modules.

INSTALLATION

You install Tree::DAG_Node, as you would install any perl module
library, by running these commands:

perl Makefile.PL
   make
   make test
   make install

If you want to install a private copy of Tree::DAG_Node in your home
directory, then you should try to produce the initial Makefile with
something like this command:

perl Makefile.PL LIB=~/perl

Then you may need something like
  setenv PERLLIB "$HOME/perl"
in your shell initialization file (e.g., ~/.cshrc).

See perldoc perlmodinstall for more information on installing modules.

DOCUMENTATION

POD-format documentation is included in DAG_Node.pm.  POD is readable
with the 'perldoc' utility.  See ChangeLog for recent changes.

MACPERL INSTALLATION NOTES

Don't bother with the makefiles.  Just make a Tree directory in your
MacPerl site_lib or lib directory, and move DAG_Node.pm into there.

SUPPORT

Questions, bug reports, useful code bits, and suggestions for
Tree::DAG_Node should just be sent to David Hand, <cogent@cpan.org>.

AVAILABILITY

The latest version of Tree::DAG_Node is available from the Comprehensive
Perl Archive Network (CPAN).  Visit <http://www.perl.com/CPAN/> to find
a CPAN site near you.

This program is free software. It is released under the Artistic License 2.0.
See L<http://opensource.org/licenses/Artistic-2.0>.

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