Organising information: trees

silvio.peroni@unibo.it 0000-0003-0530-4305 @essepuntato

Computational Thinking and Programming (A.Y. 2021/2022)

Second Cycle Degree in Digital Humanities and Digital Knowledge

Alma Mater Studiorum - Università di Bologna

Creative Commons Attribution 4.0 International License

Communication 1

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Historic hero: Gabriel Garcia Marquez

He was a novelist, and won the Nobel Prize for Literature in 1982

He is mainly known for his novels: One Hundred Years of Solitude, Love in the Time of Cholera

In the One Hundred Years of Solitude he narrates the story of seven different generations of people of the Buendia family

At the beginning of the book there is the Buendia family tree, for helping the reader to follow the story

Trees in recursive calls

Recursive algorithm: we have used a tree for showing the execution of the recursive calls to the Fibonacci algorithm implemented by means of the divide and conquer approach

Other uses of trees

Dealing with markup languages so as to associate specific roles to the various parts of a text

Example from Alice's Adventure in Wonderland by Carroll:

Alice was beginning to get very tired of sitting by her sister on the bank, and of having nothing to do: once or twice she had peeped into the book her sister was reading, but it had no pictures or conversations in it, “and what is the use of a book,” thought Alice, “without pictures or conversations?”

So she was considering in her own mind, (as well as she could, for the hot day made her feel very sleepy and stupid,) whether the pleasure of making a daisy-chain would be worth the trouble of getting up and picking the daisies, when suddenly a white rabbit with pink eyes ran close by her.

Markup: example

Markup: example

Markup: example

Markup: example

Markup: example

From boxes to trees

This approach of enclosing part of a text within a labelled box is called markup

Several markup languages have been defined in the past so as to enable such kinds of annotations on a text

Even if it is not extremely clear at a first sight, such organisation of boxes describes a precise hierarchy between them, that we can actually abstract as a tree

The bigger box (i.e. book) contains smaller ones (i.e. chapters), that contain the even smaller ones (i.e. paragraphs), and so on

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: tree example

Markup: HTML

<html>
    <head><title>Alice's Adventures in Wonderland</title></head>
    <body>
        <section role="doc-chapter">
            <p>Alice was beginning to get very tired of sitting by her sister on the bank, and of
               having nothing to do: once or twice she had peeped into the book her sister was
               reading, but it had no pictures or conversations in it, <q>and what is the use
               of a book,</q> thought Alice, <q>without pictures or conversations?</q></p>
            <p>So she was considering in her own mind, (as well as she could, for the hot day made
               her feel very sleepy and stupid,) whether the pleasure of making a daisy-chain would
               be worth the trouble of getting up and picking the daisies, when suddenly a white
               rabbit with pink eyes ran close by her.</p>
            <p>...</p>
        </section>
        <section role="doc-chapter">...</section> ...
    </body>
</html>

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree: definition

A tree is a data structure that simulates a hierarchical tree, composed by a set of nodes related to each other by a particular hierarchical parent-child relation

Tree and Python

There is no built-in implementation of the tree data structure in Python

We use the external anytree package

Constructor for nodes:
def Node(name, parent=None)

Each node must specify a name (any object, e.g. a string) and a parent – if the parent is not specified then it will assume None as value and it is implicitly defined as the root node of a tree

Example

book = Node("book")
chapter_1 = Node("chapter", book)
chapter_2 = Node("chapter", book)

paragraph_1 = Node("paragraph", chapter_1)
text_1 = Node("Alice was beginning to get very tired of sitting by "
              "her sister on the bank, and of having nothing to do: "
              "once or twice she had peeped into the book her sister "
              "was reading, but it had no pictures or conversations "
              "in it, ", paragraph_1)
quotation_1 = Node("quotation", paragraph_1)
text_2 = Node("“and what is the use of a book,”", quotation_1)
text_3 = Node(" thought Alice, ", paragraph_1)
quotation_2 = Node("quotation", paragraph_1)
text_4 = Node("“without pictures or conversations?”", quotation_2)

paragraph_2 = Node("paragraph", chapter_1) ...

The siblings of a certain parent are actually ordered among them – the order is defined by the order of insertion as a child of that particular parent

Hooks

<node>.name returns the object used as name
<node>.children returns a tuple with the child nodes
<node>.parent returns the parent node
<node>.descendants returns a tuple with the descendants of a node
<node>.ancestors returns a tuple with the ancestors of a node
<node>.siblings returns a tuple with the siblings of a node
<node>.root returns the root node of the tree where a node is contained

Rendering trees

It is possible also to visualise the tree graphically, by instantiating the class RenderTree by specifying a node as input, and then print it on screen using print

from anytree import RenderTree

renderer = RenderTree(book)
print(renderer)

# Node('/book')
# ├── Node('/book/chapter')
# │   ├── Node('/book/chapter/paragraph')
# │   │   ├── Node('/book/chapter/paragraph/Alice was…')
# │   │   ├── Node('/book/chapter/paragraph/quotation')
# │   │   │   └── Node('/book/chapter/paragraph/quotation/“and…')
# │   │   ├── Node('/book/chapter/paragraph/ thought Alice, ')
# │   │   └── Node('/book/chapter/paragraph/quotation')
# │   │       └── Node('/book/chapter/paragraph/quotation/“without…')
# │   ├── Node('/book/chapter/paragraph') …

END Organising information: trees

silvio.peroni@unibo.it 0000-0003-0530-4305 @essepuntato

Computational Thinking and Programming (A.Y. 2021/2022)

Second Cycle Degree in Digital Humanities and Digital Knowledge

Alma Mater Studiorum - Università di Bologna