LIMITS OF A SENTENCE BASED PROCEDURAL APPROACH FOR 
ASPECT CHOICE IN GERMAN-RUSSIAN MT 
Bianka BUSCHBECK, Renat¢ HENSCHEL, Iris H6SER, Gerda KLIMONOW, Andreas K(ISTNER, Ingrid STARKE 
Zentralinstitut ffir Sprachwissenscha~, Berlin 
Prenzlauer Promenade 149-152 
O-1100 Berlin 
ABSTRACT 
In this paper we discuss some problems arising in 
German-Russian Machine Translation with regard to tense 
and aspect. Since the formal category of aspect is missing 
in German the information required for generating Rus- 
sian aspect forms has to be extracted from different 
representation levels. A sentence based procedure for 
aspect choice in the MT system VIRTEX is presented 
which takes lexieal, morphological and semantic criteria 
into account. The limits of this approach are shown. To 
overcome these difficulties a human interaction compo- 
nent is proposed. 
INTRODUCTION 
Aspect is considered to bca grammatico-semanticai 
category for expressing various temporal references in 
relation to the speech act moment. Regardless of the great 
number of special meanings that can be expressed by the 
perfective or imperfectiv¢ aspect (p.asp./i.asp.), there are 
two oppositions representing the systematic or basic 
aspectual meanings, namely +TOTALITY/+LIM/TEDNESS 
VerSus -TOTAL1TY/-LIMITEDNESS (see Bondarko 1990). 
In this paper we will discuss the transfer of tense and 
aspect, a problem which arises immediately in Machine 
Translation and differS from language pair to language 
pair. This mainly depends on how aspect is expressed in 
the particular languages concerned. 
It is obvious that aspect in several languages has a 
rather heterogeneous formal reflection in the verb system. 
Aspect and tense are closely connected with each other. 
In English, e.g., the two aspect constructions perfective 
and progressive can be seen as realizing the basic contrast 
of the action viewed as complete or as incomplete (for 
details see van Eynde 1988). 
All Slavic languages on the other hand have a well- 
formed aspect system where verbs have a perfective and 
an imperfectivc aspect derived from the verbal stem by 
affixation. The translation of verbal groups from English 
into Russian, for example, seems to be possible by for- 
mulating rules which assign concrete Russian aspect 
forms to several combinations of tense and aspect in 
English, e.g. 
has been giving (present perfect continuous) 
-> zr~Ba/r (past, imperfective aspect) 
has given (present perfect) 
--> ~ra~ (past, perfective aspect) 
(ef. Apresjan 1989: 154). 
In contrast to the languages mentioned above, aspect 
meaning in German, which doubtlessly exists, has no 
explicit formal expression. Therefore, aspect information 
required for translation into Russian has to be extracted 
from different levels of text representation. This is 
necessary since without the correct choice of Russian 
aspect serious translation errors in the target language 
could occur. In our German-Russian MT project VIRTEX 
we have approached this problem by constructing a 
hierarchic procedure for aspect choice (presented in the 
next paragraphy which takes a complex of contextual, 
morphological and semantical criteria into account. If the 
aspect choice algorithm fails to select one of the two 
aspect forms, wider context (beyond the bound-aries of 
sentence) or background knowledge must be taken into 
consideration. To meet this difficulty VIRTEX is provided 
with a system of inquiries. If necessary, human 
interaction is entered to make a final decision (in the 
sense of Personal MT, see Boitet 1990). A more perfect 
solution can only be reached by a more sophisticated text 
and knowledge representation including aspectual 
characteristics. 
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A SET OF FORMAL CRITERIA 
USED BY VIRTEX 
FOR DETERMINING ASPECT AND TENSE 
The MT system VIRTEX is made to translate simple 
German main clauses into Russian including the decision 
of appropriate aspect forms for simple and complex 
verbal groups. We distinguish five different types of 
criteria all of them operating on the level of a syntactic 
surface structure enriched by semantic features: 
1. Lexkai Information 
German verbs which in every context denote 
non-resultative activities are always translated by a 
Russian verb in imperfective aspect form, e.g. arbeiten 
'to work' - > pa6OTaTT~. 
A contrasting class of verbs (siegen 'to win', er- 
reichen 'to achieve') which represents achievements (see 
Vendler 1967) can be translated in an analogous way into 
perfectiv¢ aspect forms unless the context suggests 
iterativity. 
2. Valency Frames 
Some verbs allow different readings concerning their 
semantics. These may be distinguished by the occurrence 
of certain verbal complements: 
(a) Er schrieb an einem Brief. 
'He was writing a letter.' 
-> Ou Iruca:I nHCbMO. (i.asp.) 
(b) Er schrieb einen Brief. 
'He was writing/wrote/has written a letter.' 
-> Ou rr~tca~/uan~ca~ nuc~uo. 
(both aspect forms are possible) 
Furthermore, there are German verbs which include 
several semcmes differing with regard to their termina- 
tive/aterminative usage (cf. Mehlig 1988). Such a verb is, 
e. g., the verb sprechen 'to speak'. For translating the 
terminative reading of the verb - sprechen mit jmdm. 'to 
talk with sb.' - in Russian both aspect forms can be 
used: roBopHT~/IrOroBopHT~ c xeu. Theaterminative 
reading of sprechen does not occur in connection with 
the preposition mit 'with'. In Russian the imperfective 
aspect must be chosen: 
Er sprach (vor Studenten) aber Werkstoffe. 
'He spoke (to the students) about materials.' 
-> Ou ro~opn~ (*noro~opu~) (~epe~ 
, CTyAeHTaMH) 0 UaTepua2rax. 
Such temporal distinctions of verb readings make it to 
some extent possible to choose the appropriate aspect 
form already with the help of the dictionary only. 
3. Adverbial Semantics 
Various types of adverbials may help to arrive at a 
decision. In cooecurrence with durative, iterative or 
intensity adverbials (e.g. den ganzen Tag lang 'all day 
long', h~ufig 'frequently', mehr und mehr 'more and 
more'), the imperfective aspect is chosen. If there are 
adverbials of punctual meaning (pl~tzlich 'suddenly', 
date, time) or of future events (demndchat 'soon') and no 
adverbial of the former class, the pcrfective aspect is 
preferred. Within the aspect choice algorithm (see fig. 1) 
these two classes of adverbs were named ADV-I and 
ADV-P. 
4. Tense 
If none of the aforesaid criteria applies some German 
tenses determine the aspect choice: 
Past perfect is translated to perfective aspect form, 
in the case of the present tense (pracsens futuri ex- 
cluded) the imperfective aspect is preferred. 
Future perfect is translated into future using the 
perfective aspect if there is no indicator of subjunc- 
tive meaning which is expressed in Russian by the 
preterite form an and insertion of BepoflTnO 
'probably'(see the symbol PRT+VEROJ^TNO in fig.l). 
5. Aktionsart Type and Additional Conditions 
In the case of the remaining tense forms (not listed 
in 4.), choice of aspect depends on the verbal semantics. 
There are distinctions between durative verbs (warren 'to 
wait', diskutieren 'to discuss'), verbs with a resultative 
meaning (ertu)hen 'to raise', definieren "to define') or 
verbs such as aufz/lhlen 'to enumerate', produzieren 'to 
produce', which are characterized by such properties as 
limitedness, repeafibility, general faetitive meaning, 
named IIM+ITER in fig. I . In these cases the existence of 
a direct object, its number and definiteness (N4 PLUR, 
N4 BET in fig. 1) must be taken into consideration. 
For details see figure 1 showing the aspect choice 
algorithm for active voice sentences implemented in 
VIRTEX. Some of the strict decisions in this algorithm are 
preferential ones as will be discussed in the next 
paragraph. In the case of the passive voice or of modal 
constructions, different sequences of conditions are 
- 270 - 
I lexical criteria 9r lexeme-specific valency frame conditions 
ASP BY LEXICON-- I or P 
adverbial semantics 
ADV--I -- I I 
IMPERATIVE -- 
I 
ADV--P -- P 
NEG- I I 
P 
tense criteria 
PAST PERF -- P I 
PRES I 
tense, semantic subclassification and additional conditions 
FUT PERF -- ADV ANTE 
I P , DURATIVE -- I, PRT+VEROJATNO I 
P, PRT+VEROJATNO 
FUTURE DURATIVE -- LIM+ITER N4 DET -- P 
I I I P I I 
DURATIVE I 
P 
LIM+ITER-- N4 PLUR N4 DET -- P I I 
P I 
RESULT OBJECTS -- P 
' I I/P 
PERFECT -- P 
I I 
Symbols: ... yes 
I no 
I 
P 
choice of the imperfect aspect 
choice of the perfective aspect 
Figure 1. The VIRTEX aspect choice algorithm for active voice 
- 271 - 
checked in combination with the operations of passive to 
active transformation (if necessary) or structural transfer 
for certain modal constructions. 
THE ROLE OF CONTEXT 
When translating isolated sentences into Russian the 
absence of information about how to interpret the verbal 
meaning from an aspectual point of view causes major 
problems. Often the sentence is too short to fred indica- 
tors allowing for a decision between several possible 
interpretations (of. Somers 1990) which would lead to 
different results of aspect choice. In such cases it is 
obvious that by using formal criteria an unambiguous 
solution is not possible. In other words: the rigid aspect 
choice algorithm implemented in VmTEX at first com- 
pelled us to make preferential decisions although we have 
been aware of the fact that sometimes another 
interpretation of the sentence to be translated would not 
be captured. 
In the following we shall show with five examples how 
certain contexts help us to clarify the intended interpreta- 
tion of the given sentence in order to choose the proper 
aspect form. Here the term 'context' refers to what is 
expressed in the text surrounding the sentence to be 
translated or to the user's background knowledge about 
the text. As long as this kind of knowledge is not accessi- 
ble, it shall be introduced by means of a dialogue compo- 
nent. 
Current Process I Result 
(1) Der Student schrieb einen Brief. 
(la) CTyZOHT ~anlcca:~ nHCbUO. (p.asp:) 
'The student wrote/has written a letter.' 
(lb) CTy,£eUT nHcaJI rrHcbuo. (i.asp.) 
'The student was writing a letter.' 
In the first version of VmTEX designed without a user 
dialogue we preferred the interpretation by:which the 
denoted action is assumed to be completed and conse- 
quently the perfective aspect is chosen (see: (la)). For 
verifying this reading a suitable context criterion could 
be, e. g., whether another action follows (sequence of 
predicates): "Der Student schrieb einen Brief. Danach 
brachte er ihn zur Post." 'The student wrote a letter. 
After that he took it to the post office.' 
Variant (lb) is a good translation if the sentence can be 
related to a parallel situation or to an action going on 
simultaneously: "F.s war sp~t am Abend. Der Student 
schrieb einen Brief." 'It was late in the evening. The 
student was writing a letter.' 
To solve this ambiguity by dialogue the user should be 
asked whether a continuous process or a completed action 
is meant. This may be done by inserting an adverb into 
the sentence and asking the user whether the meaning 
remains unchanged. The following question should be 
asked: "Ist der Satz so gemeint: 'Der Student schrieb 
gerade einen Brief? O/n)" 'Does the sentence mean: 
The student was iust writing a letter ? (y/n)'. If the user 
says no, reading (lb) is excluded. 
Praesens Futuri / tlabitual Action 
Depending on context, German present tense can be 
used to express future events. That holds for every kind 
of verb. Indicators like adverbs help in recognizing the 
future meaning ("Er kommt morgen. " 'He will come 
tomorrow'). Even if the sentence lacks such adverbs, a 
future interpretation may be possible but we neglect this 
fact for the time being. Only if the German sentence 
contains an achievement verb (the achievement verbs 
form a subclass of the non-durative ones), the future 
interpretation seems to have a higher probability because 
this class of verbs cannot be used to denote a currently 
ongoing action: 
(2) Er ~st die Aufgaben rechtzeitig. 
(2a) OH pollIHT 3a~a ~rH so-Bpez4~. (p. asp.) 
'He will solve the tasks in time.' 
(2b) Os peruser aa~a tnf BO-BpeU~. (i.asp.) 
'He solves the tasks in time.' 
An indicator for the praesens futuri interpretation 
leading to the translation (2a) would be a context like 
"Morgen mu~ der Student die Arbeit abgeben. Ich bin 
sicher: Er ll~st die Aufgaben rechtzeitig. " 'Tomorrow the 
student has to submit the paper. I am sure: he will solve 
the tasks in time.' In this case the perfective aspect is 
necessary. But it is also possible to assign the sentence an 
iterativeJhabitual interpretation leading to sentence (2b). 
Then we have in mind rather a certain property than a 
concrete action of the person specified in the subject 
position. A context suggesting this reading could be a 
characterization of the student. 
- 272 - 
To test whether this reading is meant the user is invited 
to compare the original sentence with "Er l~st die 
Aufgaben in der Re~el rechtzeitig." 'As a rule he solves 
the tasks in time.' If the insertion is possible without 
changing the sentence meaning, the imperfective aspect 
of the verb will be chosen, otherwise we assume that the 
future interpretation holds, which is expressed by the 
per fective aspect. 
Type / Token 
Another class of verbs (such as herstellen 'to produce', 
exportieren 'to export', verkaufen 'to sell') causes a type 
of ambiguity as shown in (3): 
(3) Der Trabant wurde in der DDR verkaujg. 
(3a) Tpa6a;zT 5~ur rrpozraH B FzTP. (p.asp.) 
'The Trabant car was sold in the GDR.' 
(3b) Tpa6al4T rtpo~aBayIc~ B Fz~P. (i.asp.) 
'The Trabant car was sold in the GDR.' 
In a context like "Au{3erhalb des Landes stieB der 
Trabant aufAbsatzschwierigkeiten." 'Abroad the Trabant 
car met with sales resistance.' sentence (3) describes a 
frequentative process. In another context a single event of 
verkaufen 'to sell' could be meant: "Die Polizei befaBt 
sich noch immer mit dera Unfallauto. Es ist jetzt sicher: 
Der Trabant wurde in der DDR verkaufl. " 'The police is 
still investigating the car damaged in the accident. Now 
it is clear: the Trabant car was sold in the GDR.' 
You may observe in our example that the aspectual 
ambiguity is interrelated with an ambiguity of the 
semantic object: whereas in the first reading i t refers to 
a set of objects, Trabant is type, ill the second reading 
it denotes one concrete individual - Trabant is token. The 
distinction between type and token requires deeper 
semantic analysis which is impossible without contextual 
knowledge. 
In order to avoid the terms 'type' and 'token' within 
the dialogue, two sentences are offered to the user. He 
must decide which of them is more suitable to be used as 
a paraphrase of the original sentence. With our example, 
he must select between "Dieses Ob/ekt wurde in der DDR 
verkaufl" 'This object was sold in the GDR' and "Di__ge 
Objekte wurden in der DDR verkaufl" 'The objects were 
sold in the GDR'. If the user prefers the first paraphrase, 
the Russian perfcctivc aspect will be used, otherwise the 
irnperfcctive one. 
(4) Er 
(4a) 
General Factitive Meaning I Concrete Action 
hat Plane ausgearbeitet. 
OH pa3pa6aT~Ba:¢ n:mu~. (i.asp.) 
'He has worked out plans.' 
(4b) OH pazpaSoTag¢ IrZaHH. (p.asp.) 
'He has worked out plans.' 
The imperfective meaning (sec (4a)) is inherent in the 
source sentence when it is interpreted in the following 
way: a person has gained some experience in working out 
plans, maybe it was his professional task. Such a 
translation underlines the general faetitive meaning which 
can be emphasized by using the adverbials irgendwann 
einmal, eine Zet#ang 'some time (during his life)': "Er 
hat irgendwann einmal / eine Zeitlang Plane ausgearbei- 
tel." 'Some ti..m.¢ he worked out plans.' This is the 
preferred reading in the V\]RTEX aspect choice algorithm. 
Nevertheless, the sentence also can suggest a concrete, 
completed action, e. g., if the context refers to the result 
of this action as in "Er hat Plane ausgearbeitet. Sic 
liegen zur Ansicht aus." 'He has elaborated plans. They 
are open to inspection.' In this case the translation must 
use the perfcctive aspect. 
To test which of the two readings is the appropriate 
one, the system offers a sentence with the inserted 
adverbs as mentioned above, and the user is requested to 
compare its meaning with that of the sentence to be 
translated. 
The preference of (4a) to (4b) assumed by VIRT~ 
would be the converse if the direct object were definite. 
Further types of aspectual ambiguity may occur. In 
addition, within one aspect form it may become necessary 
to resolve temporal ambiguities, e.g.: 
Future Perfect / Subjunctive Meaning 
(5) Der Student wird die Prflfung abgelegt haben. 
(5a) CTy,~eNT C~iaCT 3I¢38MeH. 
'The student will have passed the exam.' 
(Sb) Cry~eur, Bepo~TuO, c~a~ 3I¢3a~eu. 
'The student probably passed the exam.' 
Sentences (Sa) and (Sb) exemplify that future perfect in 
German does not only express future events but more 
ol~en expresses a presumption with regard to events, ac- 
tions, etc. which took place in the past. The latter 
interpretation could be indicated by adverbs which 
- 273 
semantically contradict the future interpretation. These 
are adverbs of anteriority denoting spans or points of time 
in the past such as gestern 'yesterday', eben / gerade 
'just' or letztes Jahr 'last year'. In this ease the choice 
of the proper aspect form depends on the semantic 
subclass of the associated verb. For non-durative verbs 
the perfective aspect must be chosen, for durative verbs 
- the imperfective one. On the other hand, adverbs of 
posteriority underline the future tense interpretation. 
Without such adverbials the sentence remains ambiguous. 
Adverbs of simultaneity and those deietie adverbs which 
can express simultaneity as well as anteriority and 
posteriority do not contribute to disambiguating future 
perfect sentences because they allow for both interpreta- 
tions. 
To solve the ambiguity in example (5) the inquiry 
might be: "Nehmen Sic an, da\[3 dos bereits erfolgt ist?" 
'Do you think that it already happened?' 
When formulating the inquiries of the dialogue compo- 
nent, we followed the principle that the questions to be 
answered by the user should be made as precise and 
simple as possible and should not presuppose any special 
knowledge in linguistics. 
CONCLUSIONS 
The above examples show the necessity of taking wider 
context into account if the sentences are too short to 
make a weUfounded choice of aspect and tense. As a 
preliminary solution the integration of inquiries into the 
system was proposed. For practical use such inquiries 
may be very helpful because they allow us to improve the 
translation of isolated sentences and, moreover, of senten- 
ces taken from texts. Nevertheless, from the linguistic 
point of view there has to be further investigation in the 
field of semantics for the automatic generation of the 
appropriate aspect forms. 
In future we plan to treat aspect and tense by express- 
ing them in a deep semantic representation. This forces 
us to include wider context beyond sentence boundaries 
or extralinguistie knowledge, e.g. style and text typology, 
This can be done either in an interactive way as proposed 
in this paper or by means of knowledge based MT. 
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