A Multilingual Approach to Disambiguate Prepositions  
and Case Suffixes 
Eneko Agirre, Mikel Lersundi, David Martinez 
 
IxA NLP group 
University of the Basque Country 
649 pk. - 20.080 Donostia (Spain) 
{eneko, jialeaym, jibmaird}@si.ehu.es 
 
Abstract 
This paper presents preliminary 
experiments in the use of translation 
equivalences to disambiguate 
prepositions or case suffixes. The core 
of the method is to find translations of 
the occurrence of the target preposition 
or case suffix, and assign the 
intersection of their set of 
interpretations. Given a table with 
prepositions and their possible 
interpretations, the method is fully 
automatic. We have tested this method 
on the occurrences of the Basque 
instrumental case -z in the definitions of 
a Basque dictionary, looking for the 
translations in the definitions from 3 
Spanish and 3 English dictionaries. The 
results have been that we are able to 
disambiguate with 94.5% accuracy 
2.3% of those occurrences (up to 91). 
The ambiguity is reduced from 7 
readings down to 3.1. The results are 
very encouraging given the simple 
techniques used, and show great 
potential for improvement. 
1 Introduction 
This paper presents some preliminary experiments 
in the use of translation equivalences to 
disambiguate the interpretations of case suffixes in 
Basque. Basque is an agglutinative language, and 
its case suffixes are more or less equivalent to 
prepositions, but are also used to mark the subject 
and objects of verbs. The method is general, and 
could be as easily applied to prepositions in any 
other language. The core of the method is to find a 
preposition in the translation of an occurrence of 
the target case suffix, and select the 
interpretation(s) in the intersection of both as the 
valid interpretation(s). At this point, we have not 
used additional sources for the disambiguation, 
e.g. governing verbs, nouns, etc., but they could 
complement the technique here presented. 
In this particular experiment, the method was 
tested on the definitions of a Basque monolingual 
dictionary, using the -z instrumental as the target 
case suffix. The main reason is that we are in the 
process of building a Lexical Knowledge Base out 
of dictionary definitions, and the disambiguation 
of case suffixes and other semantic dependencies 
is of great interest. 
The method searches for the respective 
definitions in English and Spanish monolingual 
dictionaries and tries to find a preposition that is 
the translation of the target case suffix. Once the 
preposition is found, the intersection of the set of 
interpretations of both the source case suffix and 
the translated preposition is taken, and the 
outcome is stored. 
The resources needed to perform this task are 
the following: lemmatizers, bilingual dictionaries 
and monolingual dictionaries, as well as a table of 
possible interpretations of prepositions and case 
suffixes. In our case, we have used Basque, 
English and Spanish lemmatizers, Basque/English 
and Basque/Spanish bilingual dictionaries, a target 
Basque monolingual dictionary, 3 Spanish and 3 
English monolingual dictionaries.  
The method is fully automatic; the Spanish and 
English monolingual dictionaries are accessed 
from the Internet, and the rest are local, installed 
in our machines. The manual work has been to 
build the table with possible interpretations of the 
prepositions and case suffixes. 
                       July 2002, pp. 1-8.  Association for Computational Linguistics.
                 Disambiguation: Recent Successes and Future Directions, Philadelphia,
                             Proceedings of the SIGLEX/SENSEVAL Workshop on Word Sense
The paper is structured as follows. Section 2 
presents the method for disambiguation in detail. 
Section 3 introduces the interpretations for the 
case suffix and the prepositions. The results are 
shown in Section 4, which are further discussed in 
Section 5. Finally, section 6 presents the 
conclusions and future work.  
2 Method for disambiguation 
The goal of the method is to disambiguate 
between the possible interpretations of a case 
suffix appearing in any text. We have taken as the 
target text the definitions from a monolingual 
Basque dictionary Euskal Hiztegia, EH in short 
(Sarasola, 1996). The method consists on five 
steps:  
• Extraction of the definitions in EH where the 
target case suffix occurs.  
• Search of on-line Spanish and English 
dictionaries to obtain the translation 
equivalent of the definitions.  
• Extraction of the target preposition from the 
translation definitions.  
• Disambiguation based on the intersection of 
the interpretations of case suffix and 
prepositions.  
We will explain each step in turn. 
2.1 Extraction of relations from EH 
Given a case suffix, in this step we will search the 
EH dictionary for occurrences of the case suffix. 
We first lemmatize and perform morphological 
analysis of the definitions (Aduriz et. al, 1996). 
The definitions that contain the target case suffix 
in a morphological analysis are extracted, storing 
the following information: the Basque dictionary 
entry of the definition, the lemma that has the case 
suffix, the case suffix, and the following lemma.  
Below we can see a sample definition, its 
lemmatized version, and the two triples extracted 
from this definition. The occurrences of the 
instrumental -z are shown in bold. 
 
Ildo iz. A1 Goldeaz lurra irauliz 
egiten den irekidura luzea
1
  
                                                      
1
 The literal translation of the definition is the 
following : furrow, a long trench produced turning 
 
/<@@lema ildo>/<ID>/ 
/<@@Adiera_string A1.>/<ID>/ 
/<@@Kategoria iz. >/<ID>/ 
"<Goldeaz>" 
  "golde"  IZE ARR DEK INS NUMS MUGM  
"<lurra>" 
  "lur"  IZE ARR DEK ABS NUMS MUGM  
"<irauliz>" 
  "irauli"  ADI SIN AMM PART DEK INS MG  
"<egiten>" 
  "egin"  ADI SIN AMM ADOIN ASP EZBU  
"<den>" 
  "izan"  ADL A1 NOR NR_HU ERL MEN ERLT  
"<irekidura>" 
  "irekidura"  IZE ARR DEK ABS MG  
"<luzea>" 
  "luze"  ADJ IZO DEK ABS NUMS MUGM  
"<$.>" 
  PUNT_PUNT 
 
golde#INS#lur
2
 
irauli#INS#egin 
 
Extracting lemma-suffix-lemma triples in this 
simple way leads to some errors (cf. section 5.1). 
For instance, the first triple should rather be the 
dependency golde#INS#irauli (plow#with#turn, to 
be read in reverse order). We will see that even in 
this case we will be able to obtain correct 
translations and disambiguate the preposition 
correctly. Nevertheless, in the future we plan to 
use a syntactic parser to identify better the lemmas 
that are related by the case suffix.  
2.2 Search for Spanish/English 
translations 
After we have a list of entries in the Basque 
dictionary that contain the lemma-suffix-lemma 
triple, we search for their equivalent definitions in 
Spanish and English. We first look up the entry in 
the bilingual dictionary, and then retrieve the 
                                                                                   
over the ground with a plow.  
2
 The translation of the first triple is plow#with#ground, 
to be read on reverse. The translation of the second is 
turn#NULL#produce, to be also read on reverse. In this 
second triple the instrumental case suffix is not 
translated explicitly by a preposition, but by a syntactic 
construct. 
definitions for each of the possible translations 
from the monolingual dictionaries. 
We use two bilingual and 6 monolingual 
Machine Readable Dictionaries: Morris 
Basque/English dictionary (Morris, 1998) Elhuyar 
Basque/Spanish dictionary (Elhuyar, 1996); 
English monolingual on-line dictionaries are: 
Cambridge (online), Heritage (online), and 
Wordsmyth (online); and Spanish monolingual 
on-line dictionaries are: Colmex (online), Rae 
(online), and Vox (online). The Basque dictionary 
and the bilingual dictionaries are stored in a local 
server, while the monolingual dictionaries are 
accessed from the Internet using a wrapper. 
The incomplete list of the translation of ildo 
(furrow in English, surco in Spanish) is shown 
below. Note that we got two different definitions 
for surco, coming from different Spanish 
dictionaries. 
 
furrow#A long , narrow , shallow 
trench made in the ground by a 
plow  
 
surco#Excavación alargada , angosta y 
poco profunda que se hace 
paralelamente en la tierra con el 
arado , para sembrarla después  
 
surco#Hendedura que se hace en la 
tierra con el arado  
2.3 Extraction of Spanish/English 
equivalent relations 
Given a list of definitions in Spanish and English, 
we search in the definition the translation of the 
Basque triple found in step 2.1, that is, we look for 
a triple of consecutive words where the first word 
is the translation of the last word in the Basque 
triple, the second word is a preposition (which 
corresponds to the Basque suffix) and the third 
word is the translation of the first word in the 
Basque triple. Between the preposition and the last 
word in the triple we allow for the presence of a 
determiner or an adjective in the text. More 
complex patterns could be allowed, up to full 
syntactic analyses, but at this point we follow this 
simple scheme. 
Below we can find the triples for 
golde#INS#lur, obtained from the three definitions 
above. One triple is obtained twice from two 
different definitions. 
 
furrow#ground#by#plow 
surco#tierra#con#arado 
surco#tierra#con#arado 
 
Definitions that do not have a matching triple 
are discarded, leaving Basque triples without 
matching triple ambiguous. For instance we could 
not find triples for irauli#INS#egin(cf. example in 
section 2.1). The instrumental suffix is sometimes 
translated without prepositions (in this case “… 
made turning …”). 
Looking up the bilingual dictionaries for 
translation requires lemmatization and Part of 
Speech tagging. For English we use the TnT PoS 
tagger (Brants, 2000) and WordNet for 
lemmatization (Miller et al., 1990). For Spanish 
we use (Atserias et al., 1998).  
2.4 Disambiguation 
For each Basque case suffix, Spanish preposition 
and English preposition we have a list of 
interpretations (cf. Table 1). We assign the 
interpretations of the preposition to each 
Spanish/English triple. The intersection of all the 
interpretations is assigned to it. 
Continuing with out example, we can see that 
the intersection between the interpretations of the 
English by preposition (three interpretations) and 
the interpretations of the Spanish con preposition 
(four interpretations) are manner and instrument. 
Therefore, we can say that the Basque 
instrumental case interpretation in this case will 
be manner or instrument. 
 
furrow#ground#by a#plow# 
manner instrument during-time 
surco#tierra#con el#arado# 
manner instrument cause containing 
 
golde#INS#lur#instrument manner 
3 Interpretations for the 
instrumental case suffix and 
equivalent prepositions 
The method explained in the previous section is 
fully automatic, and it only requires the list of 
interpretations for each case suffix and 
preposition. In this work, we want to evaluate if 
the overall approach is feasible, so we selected 
Basque as the target language and a single case 
suffix, -z the instrumental case. Table 1 shows the 
list of possible interpretations and Table 2 and 3 
examples for each interpretation. 
The sources for the interpretations of the 
instrumental case have been a grammar of Basque 
(Euskaltzaindia, 1985) and a bilingual dictionary 
(Elhuyar, 1996). Possible interpretations for 
Spanish and English prepositions have been taken 
from an English dictionary (Cambridge, online), a 
Spanish dictionary (Vox, online) and a Spanish 
grammar (Bosque & Demonte, 1999).  
For this work we have taken a descriptive 
approach, but other more theoretically committed 
approaches are also possible. The overall method 
is independent of the set of interpretations, as it 
only needs a table of possible interpretations in the 
style of Table 1. Section 5.4 further discusses 
other alternatives. 
In order to disambiguate the occurrences of the 
instrumental case suffix we have taken the 
Spanish and English translations for this case 
suffix. The list of possible translations is 
preliminary and covers what we found necessary 
to make this experiment. Table 1 shows the list of 
prepositions and interpretations for Spanish and 
English. Examples of the interpretations can be 
found in Table 2. The Spanish preposition de had 
the same interpretations as the instrumental case 
suffix (cf. Table1), so it was discarded. 
4 Results 
The instrumental case occurs in 4,004 different 
definitions in the EH dictionary. The algorithm in 
Section 2 was applied to all these definitions, 
yielding a result for 125 triples, 3.1% of the total. 
The triples for which we had an answer were 
tagged by hand independently, i.e. not consulting 
the results output by the algorithm. The hand-
tagged set constitutes what we call the gold 
standard. 
A single linguist made the tagging, consulting 
other teammates when in doubt. Apart from 
marking the interpretation, there were some other 
special cases. 
1. In some of the examples, the instrumental 
case was part of a more complex scheme, and 
was tagged accordingly: 
• Part of a postposition (XPOST), e.g. -en 
bidez (by means of) or -en ordez (instead 
of). 
• Part of a conjunction (XLOK), e.g. batez 
ere (specially). 
• Part of a compounded suffix –zko 
(XZKO), which results from the 
aggregation of the instrumental –z  with 
the location genitive -ko. 
2. There were three errors in the lemmatization 
process (XLEM), due to lexicalized items, e.g. 
gizonezko (meaning male person).  
3. Finally, the relation in the definition was 
sometimes wrongly retrieved, e.g.  
• The triple would contain the determiner or 
an adjective instead of the dependencies. 
We thought that the algorithm would be 
able to work well even with those cases, 
so we decided to keep them. 
• The triple contains a conjunction (X): 
these were tagged as incorrect. 
Table 4 shows the amount of such cases, 
alongside the frequency of each interpretation. 
The most frequent interpretation is instrument. In 
seven examples, the linguist decided to keep two 
interpretations: instrument and manner. In a single 
example, the linguist was unable to select an 
interpretation, so this example was discarded. 
The output of the algorithm was compared 
with the gold standard, yielding the accuracy 
figures in Table 5. An output was considered 
correct if it yielded at least one interpretation in 
common with the gold standard. The accuracy is 
given for each dictionary in isolation, or merging 
all the results (as mentioned in section 2, when 
two dictionaries propose interpretations for the 
same triple, their intersection is taken). The 
remaining ambiguity is 3.1 overall. 
 
 Basque English Spanish 
 -z (ins.) of by with in de con a en 
theme x x  x x  x  
during-time x x x   x    
instrument x  x x x x x  x 
manner x x  x x x x x 
cause x x  x x x x   
containing x x  x x x x   
matter x x   x    
Table 1: interpretations for the instrumental case in Basque and its equivalents in English and Spanish. 
 
 Basque English
theme Seguru nago horretaz 
Matematikaz asko daki 
I’m sure of that 
He’s an expert in maths 
during-time Arratsaldez lasai egon nahi dut 
Gauez egin dut 
I like to relax of an evening 
I did it by night 
instrument Autobusez etorri naiz 
Belarra segaz moztu 
Euskaraz hitz egin 
I have come by bus 
To cut grass with a scythe 
To speak in Basque 
manner Animali baten hestea betez egindako haragia
 
Ahots ozen batez 
A meat preparation made by filling an 
animal intestine 
In a loud voice 
cause Haren aitzakiez nekatuta nago  
Beldurrez zurbildu 
Kanpoan lan egitea baztertu zuenez, lan-
aukera ederra galdu zuen 
Sick of his excuses 
To turn white of fear 
In refusing to work abroad, she missed an 
excellent job opportunity 
containing Edalontzia ardoz beteta dago 
Txapelaz dagoen gizona 
Ilez estalia 
The glass is full of wine 
The man with the beret on 
Cover in hair 
matter Armairua egurrez egina dago The wardrobe is made of wood 
Table 2: examples in Basque and English for the set of possible interpretations. 
 
 Basque Spanish 
theme Mariaz aritu dira 
Honetaz ziur naiz 
Han mencionado a  Maria 
Estoy seguro de esto 
during-time Gauez egin dut Lo he hecho de noche 
instrument Belarra segaz moztu 
Euskaraz hitz egin 
Hiria harresiz inguratu dute 
Cortar la hierba con la guadaña 
Hablar en vasco 
Han cubierto la ciudad de murallas 
manner Oinez etorri zen 
Ahots ozen batez 
Bere familiaren laguntzaz erosi zuen 
Berdez margotzen ari dira 
Vino a pie 
En voz alta 
Lo compró con la ayuda de su familia 
Lo estan pintando de verde 
cause Beldurrez zurbildu 
Maitasunez hil 
Con el miedo me quedé pálido 
Morir de amor 
containing Edalontzia ardoz beteta dago 
Txapelaz dagoen gizona ikusi dut 
El baso esta lleno de vino 
He visto a un hombre con boina 
matter Armairua egurrez egina dago El armario está hecho de madera 
Table 3: examples in Basque and Spanish for the set of possible interpretations. 
Table 4 also shows the most frequent baseline 
(MF), constructed as follows: for each occurrence 
of the suffix, the three most frequent 
interpretations are chosen. The accuracy of this 
baseline is practically equal to that of the 
algorithm. Note that the frequency is computed on 
the same sample where it is applied, yielding 
better results than it should. 
5 Discussion 
The obtained results show a very good accuracy, 
leaving a remaining ambiguity of 3.1 results per 
example. This means that we were able to discard 
an average of 4 readings for each of the examples, 
introducing only 5.5% of error. The results are 
practically equal to the most frequent baseline, 
which is usually hard to beat using knowledge-
based techniques. 
Coverage of the method is very low, only 
2.3%, but this was not an issue for us, as we plan 
to couple this method with other Machine 
Learning techniques in a bootstrapping 
framework. Nevertheless, we are still interested in 
increasing the coverage, in order to obtain more 
training data. 
Next, we will analyze more in depth the causes 
of the low coverage, the sources of the errors and 
ambiguity and the interpretations of case suffixes 
and prepositions. 
5.1 Sources of low coverage 
As soon as we started devising this method, it was 
clear to us that the coverage will be rather low. 
The main reason is that different dictionaries tend 
to give different details in their definitions, or use 
differing paraphrases. This fact is intrinsic to our 
method, and accounts for the large majority of 
missing answers. 
On the other hand, the simple method used to 
find triples means that a change in the order of the 
complements will cause our method to fail 
looking for a translation triple. Syntactic analysis, 
even shallow parsing methods, will help increase 
the coverage. 
Another source of discarded triples are the 
cases where the suffix is not translated by a 
preposition, e.g. the relation is carried out by a 
subject or direct object. When syntactic analysis is 
performed, we 
interpretations of the oth
5.2 Sources of
Only five errors w
were caused by
especially when
determiner instead of the re
- xixta/prick
needle 
- luma/feedl
a submarine 
There errors
parser. Other wr
# interpretation 
   8 XPOST 
1XLOK 
12 XZKO 
   3 XLEM 
   9 X 
1 No interpretation 
34 Total discarded 
  37 instrument 
  35 containing 
   7 instrument manner 
6 manner 
5 theme 
   1 cause 
0 matter 
0 during-time 
Table 4: fre
 
Dictionary tot
cambridge 16 
Am. heritage
wordsmith 26 
Colmex 10 
vox_ya 7 
Rae 26 
overall  
MF baseline 
Table 5: result
combination fo
also plan to incorporate the 
er syntactic relations. 
 error  
e made by the algorithm, which 
 the wrong triple pairings, 
 the Basque triple contained a 
lated word. Examples: 
: punta batez osatua/made by a 
e: odi batez osatua/wake made by 
 could be avoided using a syntactic 
ong pairings were caused by 
91 Total kept 
quency of tags in gold standard. 
al correct accur. ambig.
15 0.938 4.0
34 32 0.941 3.2
26 1.000 3.7
9 0.900 2.6
7 1.000 2.8
25 0.962 2.8
91 86 0.945 3.1
91 85 0.934 3.0
s for each of the dictionaries, overall 
r all and the most frequent baseline. 
errors in the English PoS tagger, or chance made 
the algorithm find an unrelated definition.  
5.3 Remaining ambiguity 
The amount of readings left by our method in this 
experiment is rather high, around 3.1 readings 
compared to 7 possible readings for the 
instrumental. This is a strong reduction but we 
would like to make it even smaller. 
We plan to study which is the source of the 
residual ambiguity. Alternative sets of 
interpretations (cf. Section 5.4) with coarser 
grained differences and smaller ambiguity, could 
yield better results. Another alternative is to 
explore more infrequent translations of the case 
suffixes, which might yield a narrower overlap. 
This is the case for the instrumental case suffix 
being translated with from, up, etc. 
5.4 Interpretations of case suffixes and 
prepositions 
Different authors give differing interpretations for 
prepositions. It has been our choice to take a 
descriptive list of possible interpretations from a 
set of sources, mainly dictionaries and grammar 
books. 
This work covers only the instrumental case 
suffix and its translations to English and Spanish. 
If tables for all case suffixes and prepositions were 
built, the method could be applied to all case 
suffixes and prepositions, yielding disambiguated 
relations in all three languages. 
More theoretically committed lists of 
interpretations (Dorr et al., 1998; Civit et al., 
2000; Sowa, 2000) should also be considered, but 
unfortunately we have not found a full account for 
all prepositions. If such a full table of 
interpretations existed, it could be very easy to 
apply our method, and obtain the outcome in 
terms of these other interpretations. 
6 Conclusion and further work 
This paper presents preliminary experiments in the 
use of translation equivalences to disambiguate 
prepositions or case suffixes. The core of the 
method is to find translations of the occurrence of 
the target preposition or case suffix, and assign the 
intersection of their set of interpretations. The 
method is fully automatic, given a table with 
prepositions and their possible interpretations.  
We have tested this method on the occurrences 
of the Basque instrumental case -z in the 
definitions of a Basque dictionary. We have 
searched the translations in the definitions from 3 
Spanish and 3 English dictionaries.  
The results have been that we are able to 
disambiguate with 94.5% accuracy 2.3% of those 
occurrences (up to 91). The ambiguity is reduced 
from 7 readings down to 3.1. We think that these 
are very good results, especially seeing that there 
is room for improvement.  
More specifically, we plan to apply surface 
syntactic analysis to better extract the dependency 
relations, which is the main source of errors. We 
would like to study other inventories of 
preposition interpretations, both in order to have 
better theoretical foundations as well as to 
investigate whether coarser grained distinctions 
would lead to a reduction in the ambiguity.  
In the future, we plan to explore the possibility 
to feed a Machine Learning algorithm with the 
automatically disambiguated examples, in order to 
construct a full-fledged disambiguation algorithm 
following a bootstrapping approach. On the other 
hand, we would like to apply the method to the set 
of all prepositions and case suffixes, and beyond 
that to all syntactic dependencies. The results will 
be directly loaded in a Lexical Knowledge Base 
extracted from the Basque dictionary (Ansa et al., 
in prep.). 
We also plan to explore whether this method 
can be applied to free running text, removing the 
constraint that the translations have to be 
definitions of the equivalent word. 
Finally, this technique could be coupled with 
techniques that make use of the semantic types of 
the words in the context. 
Overall, we found the results are very 
encouraging given the simple techniques used, 
and we think that it shows great potential for 
improvement and interesting avenues for research. 
Acknowledgments 
Mikel Lersundi and David Martinez were 
supported by Basque Government grants AE-
BFI:98.217 and AE-BFI:01.2485. This work was 
partially funded by the MCYT HERMES project 
(TIC-2000-0335) and the EC MEANING project 
(IST-2001-34460). 

References 
Aduriz I., Aldezabal I., Alegria I., Artola X., 
Ezeiza N., Urizar R., 1996, "EUSLEM: A 
Lemmatiser / Tagger for Basque" Proc. Of 
EURALEX'96, Göteborg (Sweden) Part 1, 17-26. 
Ansa O., Arregi X., Lersundi M., ”A 
Conceptual Schema for a Basque Lexical-
Semantic Framework” (in preparation) 
Bosque, I., Demonte, V., 1999, Gramatica 
descriptiva de la lengua Española, Espasa, 
Madrid. 
Brants, T. 2000. TnT - A Statistical Part-of-
Speech Tagger. In Proceedings of the Sixth 
Applied Natural Language Processing 
Conference, Seattle, WA. 
Cambridge, online. Cambridge 
International Dictionary of English 
http://dictionary.cambridge.org/ 
Civit, M., Castellón, I., Martí, M.A. and Taulé, 
M., 2000,  “LEXPIR: a verb lexicon for Spanish” 
Cuadernos de Filología Inglesa, Vol. 9.1. Corpus-
based Research in English Language and 
Linguistics, University of Granada. 
Colmex, online. Diccionario del español usual 
en México (Colmex) http://mezcal.colmex.mx 
(also accessible from 
http://www.foreignword.com 
Dorr, Bonnie J., Nizar Habash, and David 
Traum, 1998, “A Thematic Hierarchy for Efficient 
Generation from Lexical-Conceptual Structure,” 
in Proceedings of the Third Conference of the 
Association for MT in the America's, Langhorne, 
PA, pp. 333--343 
Elhuyar, 1996, Elhuyar Hiztegia, Elhuyar K.E., 
Usurbil. 
Euskaltzaindia, 1985, Euskal Gramatika Lehen 
Urratsak-I (EGLU-I), Euskaltzaindia, Bilbo. 
Heritage, online. The American Heritage
Dictionary of the English Language. 
http://www.bartleby.com/61 
J. Atserias, J. Carmona, I. Castellon, S. 
Cervell, M. Civit, L. Marquez, M.A. Marti, L. 
Padro, R.Placer, H. Rodriguez, M. Taule & J. 
Turmo “Morphosyntactic Analysis and Parsing of 
Unrestricted Spanish Text” First International 
Conference on Language Resources and 
Evaluation (LREC'98). Granada, Spain, 1998. 
Miller, G. A., R. Beckwith, C. Fellbaum, D. 
Gross, and K. Miller. 1990. Five Papers on 
WordNet. Special Issue of International Journal of 
Lexicography, 3(4). 
Morris M., 1998, Morris Student dictionary, 
Klaudio Harluxet Fundazioa, Donostia. 
Rae, online. Diccionario de la Real Academia 
de la Lengua http://buscon.rae.es/drae/drae.htm 
Sarasola, I., 1996, Euskal Hiztegia, 
Gipuzkoako Kutxa, Donostia. 
John F. Sowa, 2000, Knowledge 
Representation: Logical, Philosophical, and 
Computational Foundations, Brooks Cole 
Publishing Co., Pacific Grove, CA 
John F. Sowa, ed. (1992) Knowledge-Based 
Systems, Special Issue on Conceptual Graphs, vol. 
5, no. 3, September 1992 
Vox, online. Diccionario General de la lengua 
española VOX http://www.vox.es/consultar.html 
Wordsmyth, online. The Wordsmyth 
Educational Dictionary-Thesaurus 
http://www.wordsmyth.net 
