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<b>Data Structures and Algorithms
with Object-Oriented Design Patterns in C++</b><br>
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<H1><A NAME="SECTION0011800000000000000000">Applications</A></H1>
<P>
There are many applications for search trees.
The principal characteristic of such applications
is that a database of keyed information needs to be frequently accessed
and the access pattern is either unknown or known to be random.
E.g., <em>dictionaries</em> are often implemented using search trees.
A dictionary is essentially a container that contains ordered key/value pairs.
The keys are words is a source language and,
depending on the application,
the values may be the definitions of the words or
the translation of the word in a target language.
<P>
This section presents a simple application of search trees.
Suppose we are required to translate the words in an input file
one-by-one from some source language to another target language.
In this example, the translation is done one word at a time.
I.e., no natural language syntactic or semantic processing is done.
<P>
In order to implement the translator we assume that there exists a text file,
say <tt>"dict.txt"</tt> which contains pairs of words.
The first element of the pair is a word in the source language
and the second element is a word in the target language.
To translate a text, we first read the words and the associated translations
and build a search tree.
The translation is created one word at a time
by looking up each word in the text.
<P>
Program <A HREF="page349.html#progapp07c" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page349.html#progapp07c"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A> gives an implementation of the translator.
Two functions are given, <tt>ReadDictionary</tt> and <tt>TranslateText</tt>.
The first function takes a reference to a <tt>SearchTree</tt> instance
which is used to hold the pairs of words.
Notice, this implementation works with all the search tree types
described in this chapter
(e.g., <tt>BST</tt>, <tt>AVLTree</tt>, <tt>MWayTree</tt>, and <tt>BTree</tt>).
<P>
<P><A NAME="23636"> </A><A NAME="progapp07c"> </A> <IMG WIDTH=579 HEIGHT=544 ALIGN=BOTTOM ALT="program23633" SRC="img1419.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/img1419.gif" ><BR>
<STRONG>Program:</STRONG> Application of Search Trees--Word Translation<BR>
<P>
<P>
The <tt>ReadDictionary</tt> reads pairs of strings
from the file <tt>"dict.txt"</tt> (lines 6-7).
The <tt>Association</tt> class defined in Section <A HREF="page125.html#secadtsassociations" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/html/page125.html#secadtsassociations"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif" tppabs="http://dictator.uwaterloo.ca/Bruno.Preiss/books/opus4/icons/cross_ref_motif.gif"></A>
is used to contain the key/value pairs.
A new instance is created for each key/value pair
which is then inserted into the search tree (lines 8-9).
The process of building the search tree terminates
when the end-of-file is encountered.
<P>
The <tt>TranslateText</tt> function takes as its lone argument
a reference to a search tree which is assumed to contain
the set of key/value pairs read in
by the <tt>ReadDictionary</tt> function.
The <tt>TranslateText</tt> function reads words one at a time from the
standard input, <tt>cin</tt>,
and writes the translation of each word on the standard output, <tt>cout</tt>.
Each word is looked up as it is read (lines 18-19).
If no key matches the given word,
the word is printed followed by a question mark (lines 20-21).
Otherwise, the value associated with the matching key is printed (lines 24-26).
<P>
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