Version 0 of Deep copy and persistence of a BWidget's Tree

ABU 21 Jun 2005

 *** EDITING IN PROGRESS ***

This article introduces some new general operations that can be applied to a BWidget's Tree.

BWidget's Tree (from now on, "bw-tree") lacks in operations for persistance-storage and for deep (recursive) copy

This article provides a tcl-code implementation and examples aimed to overcome these lacks.

Well, I think we can start with a botanical metaphor ...

If we think at a bw-tree as a live tree, we could start thinking at a dried-tree as a synthetized clone of a bw-tree, i.e. a new kind of a copy of (a part of) a bw-tree.

This dried-tree is not a bw-tree; it is a derived from a bw-tree, but it cannot be handled with the usual bw-tree methods.

But there are many things we can do with a dried-tree :

We can graft a dried-tree in a live tree. Once grafted, the dried-tree becomes a 'live' part of the tree.

Moreover, we can also store the dried-tree in a box (a file) so that the bw-tree can be revitalized when the application re-starts ( or in a new application )

_: I believe we could review the whole terminology, converting the botanical terms in an proper graph-theory terminology ... this is not important here; purpose of this article is to discuss an extensions, determine its completeness and coherence, and discover its limitations.

That's the leading metaphor, now let's develope the idea ...

We need a way to create copies of a (part of a ) bw-tree.
These copies should be persistent, that is, they should survive after the application quits.

Let's call them dried-trees.

A dried-tree is a compact linear notation for storing the structure and contents of a BWidget's tree (bw-tree).
dried-tree can be used for restoring the original bw-tree,

but they can also be used for grafting, that is, they can be inserted under a node of an existing bw-tree.

Summarizing, we need new methods to:

create a dried-tree from a (sub-)bw-tree
graft the dried-tree under a node of a bw-tree (the original bw-tree or a different bw-tree)
store the dried-tree in a file
get a dried-tree from a file ( and then graft in a bw-tree)

Before looking at the core tcl-code for these new operations, I think it is important to look at some use cases:

Let's start creating a (classic) bw-tree ...

  #
  # this is our basic sample tree
  #
 package require BWidget
 pack [Tree .tree]
 .tree insert end root a  -text Aaa
 .tree insert end root b  -text Bbb
 .tree insert end root c  -text Ccc
 .tree insert end a    a1 -text Aa1
 .tree insert end a    a2 -text Aa2
 .tree insert end c    c1 -text Cc1
 .tree insert end c    c2 -text Cc2

  # some decorations ... 
 set font1 {Courier 10 bold}
 set font2 {Times 10 italic}
 set font3 {Helvetica 10 bold}

 .tree itemconfigure a  -font $font1 -fill blue
 .tree itemconfigure a1 -font $font1 -fill blue
 .tree itemconfigure a2 -font $font1 -fill blue
 .tree itemconfigure b  -font $font2 -fill gray
 .tree itemconfigure c  -font $font3 -fill red
 .tree itemconfigure c1 -font $font3 -fill red
 .tree itemconfigure c2 -font $font3 -fill red

Get a clone

 # clone the 'c' subtree
 set myDriedTree [BWidget::Tree::clone .tree c]

Graft it under the "a" node (at position 1)

 BWidget::Tree::graft $myDriedTree .tree "a" 1

Graft it in a new tree (under the root node)

 toplevel .new ; pack [Tree .new.tree]
 BWidget::Tree::graft $myDriedTree .new.tree root end

Save it in a persistent store (a file)

 BWidget::Tree::store $myDriedTree driedA.dat

Retrieve a dried-tree from a file

 set myDriedTree [BWidget::Tree::load driedA.dat]
  # .. then you can start grafting in a bw-tree ....

The core tcl-code

  .. to do ...

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