COMMENT VISUALISER LE TEMPS ET L'ASPECT ?
Gérard LIGOZAT - Michael ZOCK LIMSI, Langage & Cognition B.P. 133, 91403 Orsay Cedex / France courrier électronique : ligozat @ limsi.fr, ou, zock @ limsi.fr Nous allons décrire ci-dessous une extension d'un système interactif de génération de phrases. Après une description de SWIM,—acronyme de See What I Mean ?— nous allons discuter la façon dont on communique au système des notions relatives au temps et à l'aspect.
Avec SWIM nous poursuivons trois objectifs : (a) assister un étudiant dans l'apprentissage d'une langue, plus précisément aider l'apprenant à passer des idées aux phrases (production du langage); (b) visualiser la relation sens-forme.; (c) fournir un environnement voisin des conditions dans lesquelles on apprend naturellement une langue.
Savoir parler une langue n'est pas inné, c'est le résultat d'un apprentissage. Selon le cadre on parle d'apprentissage naturel (on apprend dans le pays même où est utilisée cette langue) ou d'apprentissage institutionnel (enseignement). Une différence fondamentale entre les deux types d'apprentissage se situe au niveau du contrôle. Dans un cas l'apprenant est actif (apprentissage naturel), - il utilise la parole pour résoudre un problème le concernant (il cherche à obtenir des informations, il veut vérifier quelque chose, etc.) - tandis que dans l'autre cas il est essentiellement réactif, c'est-à-dire qu'il ne parle que lorsqu'on le lui demande.
L'inconvénient majeur de l'apprentissage naturel est lié au fait que l'apprenant se trouve dans des situations où tout change constamment : la situation discursive, les buts ou les intentions de communication, les contenus et les formes linguistiques correspondantes. Cela est normal, car l'objectif est la communication — faire passer un message en vue d'un but donné — et non la fixation, l'explication ou l'illustration systématique d'un point précis de la langue.
Quant à l'apprentissage dans un contexte scolaire (enseignement), les inconvénients en sont les suivants: (a) la situation est artificielle (on s'exerce pour apprendre la langue et non pour communiquer un message en vue d'un but donné); (b) le professeur ignore généralement la nature des besoins de l'élève. Si l'élève sait ce qu ' il veut dire, en revanche, il ignore souvent cannent le dire. Quant au professeur, il sait comment le dire, mais il ignore ce que veut dire l'étudiant.
Pour résoudre ce problème de communication entre le professeur et l'étudiant nous avons conçu un système où l'élève peut poser des questions et où le professeur répond. On notera, que c'est l'étudiant qui a l'initiative du dialogue. C'est lui qui pose des questions, et il les pose en fonction de ses besoins.
A l'heure actuelle le système a plusieurs faiblesses et un des grands problèmes est celui de l'interface conceptuelle : comment lui communiquer le contenu du message, puisqu'on ne parle pas encore cette langue ?
Nous montrons dans la deuxième partie de ce papier la façon dont l'élève communique des informations relatives au temps et à l'aspect. Ces informations sont délicates à transmettre pour au moins trois raisons : (a) il n'y a pas d'isomorphie entre les temps conceptuels et les temps grammaticaux (le "présent" peut aussi bien exprimer des événements qui ont eu lieu que des événements qui vont avoir lieu); (b) il n'y a pas de correspondance stricte entre les temps des différentes langues (c) la terminologie utilisée dans les manuels est trop abstraite. Elle pose des problèmes d'une manière générale, et à plus forte raison lorsque la catégorie métalinguistique utilisée n'a pas de correspondant dans la langue cible (le passé simple, par exemple, n'existe pas dans toutes les langues).
Partant des travaux de Reichenbach et de Vendler nous avons conçu un langage icônique pour communiquer les informations relatives au temps. Pour ce faire, nous avons complété leurs idées tout en les rendant plus accessibles à l'utilisateur (méta) linguistiquement innocent.
Mots clefs : entrée conceptuelle, génération de phrases, relations forme-sens, EIÀO
The major goal of the system described here is to provide a natural environnent' for learning to produce sentences in French. In order to achieve this goal, we have integrated the student into the process. He should be active rather than reactive, that is, he should talk not only when being asked. After all, he knows what he wants to say, what he lacks arc the means of translating his thoughts into language.
SWIM
2) Can one say linguistic form ?
3) How should one say idea ?
5) What would happen if conceptual modification ?
6) What would happen if syntactic modification ?
7) What would happen if word y instead of word x ?
8) What is the difference between form x and form y ?
Meaning-Representation
Write your m'iiIl'ik'u Sy st urn's version
present pr.rteci negativ«
Le garçon n'a pas regardées les filles.
Le garçon n'a pas regardé les filles.
Mfjinlnji-Ui'prtaentiillon
Memory of Forms
1) Ltgaricmrtgardtlofiäe
Ijt garçon n'apai rtgarit lufilli
Figure 1
The first communication-mode (how does one say <idca>?) raises an interesting problem : how to tell the computer what one wants to say (message). The fundamental question here is in what terms to code thought and access it. Obviously, there are several ways. One could ask in another natural language (translation), one could use images, or one could use some form of metalanguage.
In this paper we discuss some of the problems that arise by using a metalanguage. We then show how a special category of thought, tense, can be communicated by using a hybrid form of representation. But, before doing so let us give a short description of the system. For more details sec [ 29, 30,31 ].
The dialogue is initiated by specifying the communication mode. Let us suppose that the user had started with the first question: How does one say <idea> ? In that case the system presents a menu (type hierarchy) from which the user has to choose:
Speech act : statement, question, command Actions - processes: taxonomy of verbs
tense : present, past, future, etc. Discourse objects : taxonomy of nouns number : singular, plural communie, status : definite, indefinite, Attributes: taxonomy of attributes
The idea behind this separation is to allow the user to make a contrastivc analysis of meaning and form between
By choosing specific values from a set of alternatives, the user tells the system what he wants to say.
As one can see from Figure 1, the screen is divided into five parts. The large window at the top represents the underlying meaning of the message a student is trying to convey.
The next two windows contain respectively the user's attempt to express this meaning and the system's version. Possible mismatches between these two versions are highlighted on the screen. This allows the system to draw the student's attention to errors. Actually, by looking at Figure 1 you can see that the student made a mistake in the verb agreement "regardé". Finally, the two windows at the bottom represent, from left to right, a snapshot of the system's iremory of meaning and the user's memory of form . The former is a device to display, hence to recall the underlying conceptual representation of a specific sentence chosen from the memory of form winctow, whereas the latter is an incrementally built database (trace) of all the sentences encountered so far.
two sentences.
Past this point, the user has various options : cither he continues in the basic communication mode (How does one aay <idca> ?), or lie changes the kind of question he wants to ask. Let us suppose that he wants to build a completely different sentence. In this case he could either go through the whole routine, which is quite cumbersome, or lie could perform die conceptual changes directcly on the graph. Obviously, this latter method is much faster.^
Actually, everything you sec on die graph, except deep-case relations, is considered by the system as a variable whose value may be changed directcly by the user. In order to do so, he clicks on any of the shown attributes (verb, tense, mode, etc.) and chooses a new value. For example, if he clicks on the verb "regarder" (to watch) the system answers by displaying a list of candidates from which we must choose. By clicking on the feature "present", the system shows different values ( present, past, future, etc.) of the variable "tense", etc. livcrytime the system is given some piece of information it will change the meaning representation accordingly and, if asked, output Ute corresponding form. For example, if one started from sentence (a) asking die system to change the number of the direct object from "singular" to "plural" it would produce (b). If one asked to change the tense from "simple past" to "present perfect", it would produce (c), etc.
a) Le garçon regarda la _fJHe (the boy watched the .giri) b) Le garçon regarda .les fides (die l>oy watched Üic^irlsJ c) Le garçon a re&ardé les filles (the lK>y has watched the
As one can see, this method allows for local as well as for global changes. Actually, the dialogue described corresponds to the communication mode 5. If one changes only one value each time, asking the system to tell right away how this meaning change is reflected in form, one can very quickly build and explore a large search space. It should be noted, that this kind of dialogue between man and machine is much faster and
See communication mode 8 : What is the difference between <fonn x> and <form y> ?
^ Actually, that is one of the major advantages of abstract representations compared to, let us say, icons. Another advantage is that this kind of representation shows on-line how conceptual or pragmatic choices affect the intermediate structure, hence more or less directly the final form. In consequence, by displaying on-line die way how the intermediate structure changes after each choice, we have a means of moving from a black box to a glass box. The former only shows how changes of the input '(conceptual choices) are reflected in the output, whereas the latter also shows how discourse choices (topicalisation, word choice, etc.) affect the intermediate levels.
less tedious than it would be between a student and a teacher. The change of meaning and the system's generation of die corresponding form take about a second, even for an untrained user.
Another communication mode the system allows tor is called: What would Iiaijpen if <syntactic modification^ 'I bis mode allows die user to perforin certain transformations such as passive voice or pronouiinalization. In the latter case, the system will ask the user to specify which element he wants pronoininalizcd (the boy, the girl, or bodi). Assume that, starting from the conceptual structure underlying sentence (a), the user wants to pronominalize respectively the agent, the object, and finally both arguments. In these cases he would get the following outputs :
Il regarde la fille. (he watches the girl)
I ,c garçon la regarde, (the boy watches her)
II lu regarde. (he watches her)
By exploring and contrasting the different possibilities, die user is meant to learn how variations of meaning are reflected in form.
.1 Discussion
We have described a computerized learning environment that has several interesting features : (a) it allows a |K)tential user to learn French on his own. (b) it fosters learning through exploration (hypothesis-testing, inductive learning); (c) it allows the user to ask questions rather tlian simply answer them. As be knows best what his needs arc, he is most likely to ask the right questions at the right moment;
On the other hand, the system has also various shortcomings: (a) the linguistic coverage is extremely small : only very simple structures can be used; (b) the conceptual interface is a surface- rather than a deep-structure component (it already contains die lexical items, i.e., the program thinks in terms of the target language); (c) the sue of the discourse universe : one can only talk about a very limited range of facts; (d) the rigidity of the conceptual component : Ute order in which die meaning is conveyed is defined a priori. The choice of verbs always precedes the choice of die nouns; (e) the terminology used (metalanguage) may be inaccessible to the linguistically innocent user.
In the remainder of this paper we will only be concerned with the last point. More precisely, we will focus on die problem of conveying the notions of time, tense and aspect. For a projiosal of how to increase the power and flexibility of the conceptual component sec [33, 34],
While much attention has been devoted to die problem of representing and interpreting tense [2, 13, 13a, 13b], little, if any attention has been devoted to die problem of generating tense in the context of natural language generation. A notable exception is die work of V. Ehrich [6] who describes the properties of a situation (a convenient neutral term for making indiscriminately reference to events, actions, processes, states) in terms of category, aspect, relation, and position.
Sentence generation consists of translating a conceptual structure into a surface form. Obviously, information concerning time, tense and aspect is part of the conceptual input.
Tense can be communicated by choosing among a set of metalinguistic terms (past, present, future, etc.). These terms are actually used in schools, in text books and even in intelligent tutoring systems [7, 8). Yet this approach has several shortcomings :
(A) Students are not linguists. While notions such as "past, present, future" seem to be meaningful when we deal with simple tenses, tilings change rapidly as soon as we move to more complex tenses like present continuous, past perfect, etc. The student is certainly short of intuition when he comes across tenses for which there is no equivalent in his mother tongue.
(B) There is no one-to-one correspondance between grammatical tenses and semantic values. The "present forms" are quite often used in order to convey the meaning of the past, the present, or the future (1-4). In a similar vein, past forms can be used with a present value (5) (I just warned to ask for a salary increase) PRESENT; (C) The possibility of using a certain form depends on the context of the sentence (presence of a temporal adverbial, nature of the subject and complements).1) J'arrive à l'instant. (1 have just arrived.) PAST;
2) Je réfléchis. (I'm thinking.) PRESENT,
3) J'arrive dans un instant. (I'm coming right now.) FUTURE;
4) J'arrive. (I just arrived.) PAST, - (/ am coming.)FUTURE.
5) Je vermis vous demander une augmentation
9) Hier, j'étais content. (Yesterday, I was very glad.);
10) * Hier, j'ai été content. (Yesterday, I have been glad.); 11 ) Hier, j'ai été content d'apprendre ton retour (Yesterday, I was glad to learn that you were coming back).
While (6) is quite acceptable, its translations into past — be it the simple past (7), or past perfect (8),— need an explicit reference. Moreover, the form of the past perfect in French can only be used if one refers to an event, — the ingression of a state,— as in (11).
Icons provide a very natural way of representing tense. Several grammars for English [21] and for French [10] make use of them. We draw on these sources and adapt them for SWIM. In order to do so we provide the user with a basic set of elements for translating tense into icons ; (a) a time axis; (b) a representation of the point of speech (NOW) on the time axis; (c) a set of types of situations (state, event, etc.); (d) a frame of reference (a window); and/or (e) a point of reference.
The time axis represents the intuitive notion of time as an oriented linear structure. The time of vertical arc locates the time of utterance: on the left hand side is the past, on the right the future. The situation to be referred to can be communicated by choosing an icon from a set of alternatives (see figure 7). The last two components, the frame and the point of reference represent the way (point of view) the speaker looks at the situation.
We start by describing these basic elements and illustrate their use through examples. We then explain how these elements are related to form a coherent metalinguistic vocabulary.
The minimal machinery necessary for generating tense is composed of a time axis with a point of speech (now) and a means of locating an action/event with respect to diis point of speech (Figure 5).
O point of speech
Figure 5
Reichenbach used the following concepts to characterize tense: a point of speech (S), a point of reference (R) and a point of event (E).
Figure 6 (c) E_S,R present perfect (d) E_RJ5 past perfect / see Paul I saw Paul I have seen Paul I had seen Paul I will see Paul I will nave seen Paul
Since then the system has been extended or re-interpreted by a number of authors [3a, 12a, 12b, 24,24a, 25a,28a].
(A) Types of situation and corresponding icons: A sentence refers to some point in time (temporal situation). A situation will be represented by any of the following icons
Figure 7 : Types of situation and corresponding icons
A state is considered as covering a stretch of time widi no definite boundaries. The icon repcresenting this suggests Ulis open-endedness by having fuzzy delimiting zones. Both ongoing processes and activities have a well-defined starting point but no determined point of termination. Note however, that activities can be interrupted at any time and be reported as events. Let us suppose that "Paul was swimming", and then stopped. This can be reported by «Paul swam». Telic processes do not have this property, because dicy have some natural point of completion. If «Paul was swimming across the Channel» and then stopped swimming, we could describe Ulis situation as Paul has been swimming, but we could not say «Paul swam across the Channel.» In that case, the point of completion can be referred to, even if it is never reached: «Paul was swimming across the channel, but he never made it». The situation can also be considered as indeterminate: «Paul was swimming across the Channel when I last heard about him».
An event has both a starting point and a point of termination. It can be punctual or not. According to Reichenbach it is represented as a point or an interval, whereas we allow for the additional use of a frame. An event can also be considered with regards to the result of its occurrence. There are events with a resulting slate. In the corresponding icon, we represent this state as adjacent to the event which has brought it about. Usually, the precise nature of this resulting state needs to be inferred (cf. [10)): /( has been raining; in consequence the pavement is wet, it got colder, there are puddles in ihe street, my hairdress is spoiled, etc.
Habitual events are an undetermined number of events. The icon of habitual events is meant to suggest their resemblance to states. It should also be noted that the number of events may be conceptually indefinite. Compare: (a)/ played tennis many times last year.(b) I used to play tennis when I was a young man
In first case we are dealing widi a sequence of individual events, not with a habitual event. Hence it is quite possible to continue the dialogue by asking the following question "how many times did you play?", while this question seems quite odd in the second case.
(B) Frame of reference, point of reference: Optional elements are a frame of reference and a point of reference, both of which can be manipulated by the user. The former consists of a window which represents the period of time considered by the speaker. It is usually associated with a temporal adverbial (Yesterday Paul visited the Eiffel Tower). The point of reference can be used in order to represent some instant which plays the role of a translated point of speech (In 1980 Paul had already visited Paris twice.).
The procedure is as follows: (a) Choose a suitable type of .situation (icon) to represent the temporal structure of the situation; (b) Position the icon relative to die point of speech; (c) If necessary, introduce and position a frame and/or point of reference and position it.(d)In the overall representation, some part of the situation should be adjacent to, or included in an element of reference (point of speech, point of reference, frame of reference). If not, reexamine step (c).
Suppose we have an untensed representation of : «Paul aime la cuisine italienne» (Paul likes Italian cooking). In order to generate die tense, wc choose a state and the position of the point of speech on the time axis (Figure 8a). From this representation the corresponding time (present tense) can be generated.
Figure 8
Figure 8b conveys die same message as 8a in the past. Since no direct reference to the point of speech is available, a frame of reference is necessary. Here it plays the same role as the point of speech in figure 8a. If the user adds the adverbial «l'an passé» (last year) as a marker of reference, we get «l'an passé, Paul aimait la cuisine italienne» (Last year Paul liked Italian cooking.
Among the difficulties faced by a learner of French is the dual value of "passé composé". Consider, (Hier), j'ai écrit mon article - [ (yesterday) I wrote my paper) In one interpretation (figure 9a), the writing of the paper is considered as a past event. Locating the action within a reference frame requires the use of ah adverbial like «hier» (yesterday).
9a)Hio- j'ai écrit mon irticle (f WTOle my p«per yeslcrdsy)
This case is to be differentiated from the situation depicted in Figure 9b. Here the implicit reference is now.
The past event is considered with respect to the state resulting from it (present relevance). In fact, the same tense is used in this case in French, whereas «Yeslerday I wrote my paper» would be used in English in case (9a), and «I have written my paper» in case (9b).
Another typical case of ambiguity is the use of the "present tense" in French. The Figures 9c and 9d, while different in English, yield the same form in French. The first one (9c) signals habitual or repetitive use of the present tense, corresponding to «I play tennis». The second situation corresponds to "/ am playing tennis", implying an ongoing activity at the time of speech. Please note that the first situation does not imply any actual activity at the time of speech, but only a general validity of a kind of property. As the icon suggests, it looks very much like a state.
Our classification of types of situation (cf. also [2]) is based on conceiving the temporal structure of a situation as a result of (a) the lexical meaning, die tense and the aspect of a given verb, (b) the nature of the subject, the complements and the time adverbials.
Lexical meaning : We basically subscribe to Vendler's typology [26] who classifies situations in terms of states, activities, accomplishments and achievements. Nakhimovsky, in a more recent classification [17], introduces additional features (generic vs. specific resources for alclic processes) to Vendler's punctuality, stativity, and telicity. Our classification is based on four classes of lexical meanings, corresponding to combinations of the features: punctuality, stativity, telicity.
• punctual events (punctual, non Stative, atelic);
• states (non punctual, Stative, atelic);
• telic processes.
• atelic activities;
Aspect is related to the perspective from which a given situation is viewed. Following Comrie [4], we distinguish between perfect, perfective and imperfective aspect. In French, the imparfait (continuous past) is a typical imperfective form: a situation is considered from the inside. Perfective, on the other hand, considers a situation as a whole. Perfect is related to the consideration of a given event together with a new state which is a consequence of this event happening, for example, I have prepared some coffee.
In our system, perfect is represented by an event with a resulting state. Aspect plays a dual role: it determines the type of situation and it allows for choosing a specific frame of reference.
Lexical meaning combined with the aspect of the verb, the types of the subjects and complements, and the temporal adverbials yield the type of situation. For example, the verb écrire (to write) has an intrinsic lexical meaning : atelic activity. However, it can change :
Paul écrivit un roman (John wrote a novel) : telic process; Paul écrit des romans (John writes novels) : atelic activity; Paul écrivait un roman (John was writing a book) : ongoing process.
The following table shows how tense could be computed on the basis of an iconic representation of a situation. The system determines the position of the main part of the situation relative to the point of speech (PS). The qualification is necessary only in the case of an event with a resulting state, where the event is the main part of the situation.
If the main part of the situation is posterior to the point of speech, a future tense is chosen by default, though present tense remains a possible candidate. Using either or amounts to communicating a special modal nuance.
ï | |||
S • | |||
9c) je joue ai | tennis (I play tennis) | ||
• • | |||
• | |||
_Y | |||
*M) je joue 1 | J tennis (I am playing tennis) | ||
I enfouit activity "I 1 habitual event f
cmCDuotLi pul• event with rciulbrtf wl
r e¥cnt L_
' \ punctual event J pnïacnl perfect f ongoing activity oagoing Mite pro»
4 event \ I ovenlpunctual even* L_J oveniwithiwullin»«!* J [_ umM__
pluaque parfait jjupetfcti pro Mol perfect
If the main situation is prior to the time of speech, the conclusion depends on the presence of a point of reference (PR) prior to the time of speech. If no such point is
I^s étudiants travaillent. ) *
Ijt directeur eu entre.
( 1 ) Quand le directeur est entré dans la classe, les étudiants travaillaient (When the headmaster entered the classroom, the students were working );
(2) Quand le directeur est entré dans la classe, les étudiants ont travaillé (When the headmaster entered the classroom, the students began to work ).
Sec figure 10 _ events. So far we handle the case of quand (when), using icons and strategies similar to the ones described by Moens & Steedman [16].
The students were working when the headmisler enured the classroom.
The undents started working when the headmaster entered the classroom.
specified, and if the type of situation is an event, one can use the past perfect. In the case of an event or a punctual event, the past perfect is a stylistic alternative (polished style).
Temporal adverbials arc classified as (a) time-position adverbs (last night, on Monday); (b) as span and duration adverbs (for a month, up to 1979); or (c) as/re<juency adverbs (usually, often). Temporal adverbs constrain tense generation. Durational adverbs may enforce a habitual meaning on verbs having an intrinsic punctual meaning : «He has been diving for several months now.* Temporal subordinate clauses: In the case of simple sentences, the task of determining the tense from an icon is straightforward. More subtle strategies are needed in sentences with temporal subordinate clauses
■ before) require the use of the
_ being that his thoughts are
,„,. . —„„.,„.. expresSed in terms of concrete actions rather than in terms of a (meta)language, which is often too abstract to be meaningful to the native user.
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The first case represents an ongoing process or activity, with an event occuring somewhere in the middle of it, while the second is a sequence of two adjacent
The way in which temporal subordinate clauses reflect on the types and order of the situations has been examined in the literature ([24,15, 16]).
We have presented in this paper a method of visualizing time, tense and aspect. By using icons we have provided the user with an interface that allows him to translate abstract thought into concrete thought. The advantage conjunctions (e.g. avant que subjunctive mood.
• • | |||
/ "•...........' | |||
/ l^s étudiants ont travaillé | |||
f | • | ||
* - | |||
Le directeur est entre. | |||
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