Design and Development of a Malayalam to English Translator- A Transfer Based Approach

Latha R Nair, David Peter & Renjith P Ravindran
International Journal of Computational Linguistics (IJCL), Volume (3) : Issue (1) : 2012 1
Design and Development of a Malayalam to English Translator-
A Transfer Based Approach
Latha R Nair latha5074@gmail.com
Assistant Professor
School of Engineering
Cochin University of Science and Technology
Kochi,Kerala,682022, India
David Peter S davidpeter@cusat.ac.in
Professor
School of Engineering
Kochi,Kerala,682022,India
Renjith P Ravindran
School of Engineering renjithforever@gmail.com
Kochi,Kerala,682022,India
Abstract
This paper describes a transfer based scheme for translating Malayalam, a Dravidian language,
to English. The input to the system is a Malayalam sentence and he ouput isits equivalent English
sentence. The system comprises of a preprocessor for splitting the compound words, a
morphological parser for context disambiguation and chunking, a syntactic structure transfer
module and a bilingual dictionary. All the modules are morpheme based to reduce dictionary size.
The system does not rely on a stochastic approach and it is based on a rule-based architecture
along with various linguistic knowledge components of both Malayalam and English. The system
uses two sets of rules: rules for Malayalam morphology and rules for syntactic structure transfer
from Malayalam to English. The system is designed using artificial intelligence techniques and
can easily be modified to build translation systems for other language pairs.
Keywords: Malayalam Language, Transfer Based Approach, Machine Translation,
Morphological Parser.
1. INTRODUCTION
Work in the area of Machine translation in India has been going on for several decades.
Promising translation technology began to emerge by 1970 with the developments in the field of
artificial intelligence and computational linguistics. Machine Translation Systems in certain well-
defined domains have been successfully developed. Translation of gazette notifications, office
memorandums,and circulars has been done successfully by Mantra system developed by centre
for development for advanced computing(CDAC), Pune. Most of the systems developed are for
Hindi, the official language of India. This paper describes a translator for translating sentences in
Malayalam a Dravidian Language to English developed on a rule based architecture combined
with linguistic knowledge components of both Malayalam and English. The system has a
preprocessor for splitting the compound words, morphological parser for context disambiguation
and chunking and a bilingual dictionary. A set of rules for Malayalam morphology and rules for
syntactic structure transfer from Malayalam to English have been incorporated in the system.
Some of the organizations which are involved in the development of translation systems are:
Indian Institute of Technology (Kanpur), Center for Development of Advanced Computing (CDAC)
(Mumbai), CDAC(Pune), Indian Institute of Information Technology (Hyderabad) . They are

engaged in development of MT systems under projects sponsored by Department of
Electronics, state governments etc. since 1990[1,2]. Research on MT systems between Indian
and foreign languages and also between Indian languages are going on in these institutions.
The two major goals in any translation system development wrk are accuracy of translation and
speed. Accuracy-wise, smart tools for handling transfer grammar and translation standards
including equivalent words, expressions, phrases and styles in the target language are to be
developed. The grammar should be optimized with a view to obtaining a single correct parse and
hence a single translated output. Speed-wise, innovative use of corpus analysis, efficient parsing
algorithm, design of efficient Data Structure and run-time frequency-based rearrangement of the
grammar which substantially reduces the parsing and generation time are required [3]. A fully
automatic Machine translation system should have different modules such as morphological
analyzer, Part of speech tagger, chunker, Named entity recognizer, word sense disambiguator,
syntactic transfer module and target word generator [3]. The different techniques used for
translation differs in the number of modules used and also the way these modules are
implemented. Both rule based and statistical approaches have been tried in the implementation of
each of these modules.
The various approaches used in the MT systems for Indian languages are: Direct machine
translation systems, Rule based systems and Corpus based systems. Rule based systems do not
use any intermediate representation. This is done on a word by word translation using a bilingual
dictionary usually followed by some syntactic arrangement. [4, 5,6] 2) Rule based translation
which produces an intermediate representation, which may be a parse tree or some abstract
representation. The target language text is generated from the intermediate representation. Of
the two rule based methods, Interlingua and transfer based approach, transfer based systems are
more flexible and it can be extended to language pairs in a multilingual environment. The
Interlingua based systems can be used for multilingual translation [7]. The amount of analysis
needed in Interlingua approach is more than that in a transfer based approach. The universal
networking language has been proposed as the Interlingua by the United Nations University for
overcoming the language barrier[8]. Corpus based MT is fully automatic and requires less human
labour than rule based approaches. The disadvantage is that they need sentence aligned parallel
text for each language pair and this method can not be employed where these corpora are not
available [9, 10].
2. PREVIOUS WORK
English to Hindi MT system Mantra, developed by Applied Artificial Intelligence (AAI) group of
CDAC, Bangalore, in 1999 uses transfer based approach. The system translates domain specific
documents in the field of personal administration; specifically gazette notifications, office orders,
office memorandums and circulars. It is based on lexicalized tree adjoining grammar (LTAG) to
represent English and Hindi grammar which are used to parse source English sentences and for
structural transfer from English to Hindi [2]. This system also works well on other language pairs
such as English-Bengali, English-Telugu, English-Gujarati , Hindi-English etc and also between
Indian language pairs such as Hindi-Bengali and Hindi-Punjabi. The Mantra approach is general
but the lexicon and grammar have been limited to the specific domain of personal Administration.
It uses preprocessing tools like phrase marker, named entity recognizer, spell and grammatical
checker. It uses Earley’s style bottom up parsing algorithm for parsing. The system provides
online addition of grammar rule. The system produces multiple translation results in the case of
multiple correct parses.
English to Kannada MT system has been developed at Resource centre for Indian Language
Technology Solutions (RC_ILTS), University of Hyderabad by Dr. K. Narayan Murthy [2]. This
also uses a transfer based approach and it can be applied to the domain of government circulars.
The project is funded by Karnataka government. This system uses Universal Clause Structure
Grammar (UCSG) formalism [15]. The technique is applied to English_ Telugu translation as well.

Other systems developed using this approach are : Matra- English to Hindi MTS developed by
CDAC, Pune, Sakti- English to Marathi, Hindi and Telugu developed by IISc Bangalore and IIIT
Hyderabad, Anubaad- English to Bengali developed by CDAC, Kolkata, English to Malayalam
MTS developed by Amrita Institute of Technology.
It is found that translation between structurally similar languages like Hindi and Punjabi can be
developed easily than translation systems between Indian languages and English which differ in
the syntactic structure. The proposed translation system translates Malayalam sentences to
English sentences. Since there is a wide difference in English and Malayalam sentences the
system needs an additional modules for parsing and syntactic reordering.
3. DEVELOPMENT AND IMPLEMENTATION OF TRANSFER BASED
MACHINE TRANSLATION SYSTEM
A transfer based MT system has been developed with the following system modules 1. A
preprocessor for splitting the compound words [13] 2. a morphological parser for context
disambiguation and chunking 3. A transfer module which transfers the source language structure
representation to a target language representation. 4. A generation module which generates
target language text using target language structure. Block diagram of the same is shown in fig 1.
The grammar rules for Malayalam and some of the transfer rules for transferring source parse
tree to target parse tree are stored in two separate files. Some of the transfer rules are embedded
in the source code. The sentences stored in a source file are read one by one by the input
module and given to the preprocessor module. The final translated output is stored in another file.
FIGURE 1: Block diagram of a transfer based system
3.1 Compound Word Splitter Module
Morphological variations for words occur in Malayalam due to inflections, derivations and word
compounding. Malayalam is an agglutinative language where words of different syntactic
categories are combined to form a single word. Formation of new words by combining a noun and
a noun, noun and adjective, verb and noun, adverb and verb, adjective and noun and in some
cases all the words of an entire sentence to reflect the semantics of the sentence are very
common. The complexity of compounding in Malayalam language can be understood from the
following example.
The English version being Seetha’s cat ate a rat

The constituent words in 1 are to be separated before any further processing. Splitting has been
done at morpheme level to reduce dictionary space. The above sentence gets split as shown in 2
morpheme by morpheme translation for the sentence at 2 is :
Seetha ‘s cat a mouse (null) ate
The morpheme sequence will be as in 2 above. The sequence of morphemes is given to the
parser for chunking and word sense disambiguation. The set of inflectional suffixes for nouns and
verbs and derivational suffix for adjectives are based on previous works [11, 12]. Due to the
ambiguity in the splitting rules the system generates multiple splits for the same input sentence
and the split with least number of constituents is fed to parser.
3.2 Parser Module
Parser takes input from the splitter and does the following tasks. It groups the input sequence of
morphemes into chunks [14, 15] and performs word sense disambiguation based on morpheme
tags [16]. The chunking process finds the basic units for tree reordering. The word sense
disambiguation is required as a morpheme can have multiple tags. The parser uses a depth first
approach with backtracking [17]. The output of the parser is a parse tree for the next module. The
parser uses the syntax rules for the morpheme sequences in Malayalam sentences in the regular
expression form. A set syntax rules in the regular expression form are shown below:
1. S-> NP*VP
2. NP-> ADJ*NP | N NA
3. VP ->ADV* V VA| V VA
Rule 1 implies that a simple sentence is a sequence of noun chunks followed by a verb chunk.
Based on the second rule, a noun chunk consists of a set of adjectives followed by a noun and
suffixes like case, gender and number for nouns. According to the third rule a verb chunk consist
of a sequence of adverbs followed by a verb. Only a subset of such rules derived is shown above.
The chunks selected form groups for structural transfer to form target language structure.
A sample sentence and the parse tree generated for the sentence using the grammar rules are
shown below:
Input sentence:
English version: The police thought that the thieves who stole the chain went into forest in the
night.
Output of the splitter:
English version:chain stole theif ‘s night in forest to went that police thought
Output of the parser:

English version: CS(NC(S(NG(ADJC(S(N (chain ) V(stole) RP) NG(N(theif) PL(‘s))) NG(N(night)
NA(in)) NG(N(forest) NA(to)) V(went )) NCA(that)) S(N(police) V(thought)))
The corresponding parse tree generated is shown in Fig.2
FIGURE 2: Generated Parse tree
3.3 Syntactic Structure Transfer Module
The transfer module transfers the source language structure representation to a target language
representation. This module needs the sub tree rearrangement rules by which the source

a
b
FIGURE 3: a. Parse tree after structural transfer b. Corresponding parse tree in English

language sentence syntax tree can be transformed into target language sentence syntax tree.
The system performs most of the commonly needed reordering for Malayalam to English
translation. The tree after reordering for the above Malayalam sentence using the transfer
grammar rules using the transfer rule identified is shown in fig3(a) and its corresponding English
tree is shown in fig3(b).A set of transfer rules used by the system are shown in Table I.
Malayalam
structure
English structure
1 PP: NG P PP: P NG
2 VG: ADV V VG: V ADV
TABLE 1: A set of system transfer rules
According to the first rule the order of case suffix and noun chunk should be interchanged in a
prepositional chunk. The Second rule accords that in verbal chunk the adverb and verb should be
interchanged.
3.4 Target Sentence Generator Module
The generation module generates target language text using target language structure [18]. This
uses inter chunk dependency rules and intra chunk dependency rules. It involves lexical transfer
of verbs, transfer of auxiliary verb for tense, aspect and mood and transfer of gender, number and
person information. A depth first traversal of the target parse tree generates the following English
sentence
Input Malayalam sentence:
Correct English translation: The police thought that the thieves who stole the chain went into the
forest in the night
Sentence generated by the system:
The Police thought that thieves who stole the chain went in night to forest.
3.5 Cross lingual Dictionary
The dictionary includes most of the commonly occurring verbs, nouns, pronouns, adjectives,
inflectional and derivational suffixes, clause suffixes etc. Each entry in the file has three fields: the
root word (morpheme), the morpheme tag and its translation. The verbs in past tense have their
root words stored along with them. Since the system works with morphemes, the space required
for the dictionary is less.
TABLE 2: Lexicon

Presently the system works for sentences which contain upto two adverbial or adjectival clauses
which is commonly found in Malayalam texts. The system can be modified to handle other
sentences by adding appropriate grammar rules and transfer rules to the rule database. As the
parser is a general parser, it can handle sentences of any depth.
3.6. Implementation and Testing of the System
The system was implemented in Python language and tested with a source file which contains
1000 sentences. The sentences which follow the grammar rules were translated. A group of
results are tabulated in table 3.
4. RESULTS AND DISCUSSION
The system was tested with more than 1000 different kinds of sentences with and without
subordinate clauses which follows the identified morpheme sequences. The system returned
correct meaningful translations in most of the cases. A group of sample input sentences with the
tabulated outputs are shown in table 3 to give a correct picture of the results obtained..In around
20% of sentences the system returned the exact English version of the input sentences. In
balance translations the output sentences were meaningful but had small shortcomings due to
the following reasons:
i) The positioning of articles is not considered.
ii) Many inter chunk and intra chunk dependencies are not considered.
iii) The lexicon stores only the common translation for polysemous words.
The system takes care of word sense disambiguation based on lexical category successfully.
The compound nouns are also not handled by the system as the shallow parser cannot group
them using the current set of rules. The system output can be enhanced including rules which
can take care of the above shortcomings.
5. CONCLUSION
Various MT groups have used different formalisms best suited to their applications. Of them
transfer based systems are more flexible and it can be extended to language pairs in a
multilingual environment. A transfer based MT system has been developed for Malayalam, a
Dravidian Language which comprises of a preprocessor for splitting the compound words, a
morphological parser for context disambiguation and chunking, a syntactic structure transfer
module and a bilingual dictionary. The system was tested successfully for more than 1000
different types of sentences wherein the system returned true results for sentences which contain
two subordinate clauses. Even for sentences with more than two subordinate clauses the system

TABLE 3: Group of Tabulated results

returned translated output sentences which could give basic understanding of the input
sentences. More rules can be added to make the system to give exact translation of input
sentences in all cases. Additional modules like finding and replacing collocations, finding and
replacing named entities can also be added to the basic translator. The results obtained are
encouraging. The work can be extended to create a full fledged machine translator from any
Dravidian language to English since they all exhibit structural homogeneity.
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