CALICO Journal, Volume 9 Number 1 9

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1 PARSING, ERROR DIAGNOSTICS AND INSTRUCTION IN A FRENCH TUTOR GILLES LABRIE AND L.P.S. SINGH Abstract: This paper describes the strategy used in Miniprof, a program designed to provide "intelligent' instruction on elementary topics in French. In case of an erroneous response from a student, the program engages him/her in a Socratic dialogue. It asks specific questions about the sentence involved, thereby leading the student to identify each mistake and its correction. The systematic error detection and subsequent human-like instruction specific to the student's response is achieved by using three major functions: parsing, error diagnostics, and tutoring. The design of the system and the issues involved are discussed. Keywords: intelligent tutors, parsing, syntax, computer-assisted language instruction. Introduction The goals and potential benefits of intelligent computer assisted instruction in general, and of intelligent computer assisted language instruction in particular, are by now well recognized (see, for example, Kearsley, 1987; Polson and Richardson, 1988; Psotka et al., 1988; Wenger, 1987). Some language programs incorporating a variety of techniques and teaching strategies are already in use (see, for example, Bailin and Levin, 1989; Bailin and Thomson, 1988). Miniprof, an intelligent tutor for elementary topics in French, is being developed at Central Michigan University. The program, comprising four modules at present, is written in C for IBM personal computers. In the course of developing these modules, we experimented with different teaching strategies and system designs to deal with student errors. In two of the modules the error analysis, although quite good, was performed in an ad hoc manner and was not sufficiently systematic to be easily generalized. Adding new modules and enhancing the error analysis required considerable effort. CALICO Journal, Volume 9 Number 1 9

2 In the other two modules a system emerged which provides detailed tutoring-the kind a student gets from an instructor. When an error occurs in the student's answer to a question, the student is engaged in a dialogue specific to the error, using material from the sentence on which the student is working. This article describes the error diagnostics and subsequent instruction that leads to this teacher-like behavior. I. The Language Modules The modules described here are intended to teach students how to replace subjects with pronouns and how to give negative answers to questions. In the first module, the student is asked a question and instructed to use a subject-pronoun in the response, and in the second module, which extends the first, to respond in the negative and make the appropriate subjectpronoun substitution. In case of errors, the student is engaged in a dialogue leading to the identification of the mistakes and their correction. Figures 1 and 2 give examples of this interaction. #1 Est-ce que tu gagnes beaucoup? *Non, tu gagnes beaucoup. The question uses the pronoun "tu". Which pronoun should you use in your answer? *? Use "je". You need to answer in the negative. Use the negative in the next sentence. Answer: Non, je ne gagne pas beaucoup. #2 Est-ce que tu parles espagnol? *Non, je ne parles espagnol. The subject is "je". "parl" is correct. What should the ending be? *e Right. Your answer is negative. What do you need after the verb? *I don't know. Use "pas". Answer: Non, je ne parle pas espagnol. Figure 1. Examples #1 and #2 CALICO Journal, Volume 9 Number 1 10

3 Although the exercises are simple, the objective is to imitate the behavior of an experienced instructor. To this end, the instruction is focused on the specific error, and the instructional messages use material from the sentence in question. II. Overview of the design The two modules are based on a common internal strategy which incorporates three major components: parsing, diagnosis and tutoring. As outlined in Figure 3, the parsing and diagnosis functions analyze the student's response and record errors by setting a flag for each error uncovered. The syntax errors those at the sentence level are detected by the parser as described in section #3 Est-ce que Mike étudie beaucoup? *Non, Mike ne étudie pas beaucoup. You need to substitute a pronoun for "Mike". Which pronoun should you use? *il That's right What do you use instead of "ne" if a vowel or mute 'h' follows? *n' Right. Answer: Non, il n'étudie pas beaucoup. #4 Est-ce que vous mangez beaucoup? *Non, nous ne mangons pas beaucoup. What do you need between a 'g' and a verb ending starting with 'a' or 'o'? *? Use "e". Answer: Non, nous ne mangeons pas beaucoup. Figure 2. Examples #3 and #4 CALICO Journal, Volume 9 Number 1 11

4 III. For example, in sentence #3 of Figure 2, the parser determines that "n'" must be used instead of "ne" because the next word begins with a vowel. In sentence #4, because the root of the verb ends in "g" and is followed by "o", the parser detects that an "e" must be inserted. The other type of error involves the context and the nature of the exercise. Errors of this type are detected by the diagnostic component. This component compares the student's answer to the parse of both the question and the correct answer. In sentence #3 of Figure 2, it is the diagnostic component that determines that a pronoun has not been substituted for the noun as required by the exercise and that the correct pronoun to replace "Mike" is the 3rd person masculine singular pronoun "il". The diagnostic component also detects the errors in sentence #1 of Figure 1, where the response to a question with "tu" must be "je" and the exercise requires that the response be negative. Instruction is handled by the tutoring component which engages the student in a dialogue by asking specific question about he incorrectly answered exercise items. CALICO Journal, Volume 9 Number 1 12

5 III. The Components of the System A. Parsing Parsing offers the most effective way of specifying and checking the syntax in exercises. The parser relies on a grammar and a lexicon to perform its task. Let us look at each in turn. Sentence Grammar Our parser uses a context-free grammar augmented with the kind of constraints (for example, subject-verb agreement) found in definite clause grammars (Pereira & Shieber, 1987). A contextfree grammar (Allen 1987, Winograd 1983, Sanders & Sanders, 1989) is a set of rules defining the grammatical sentences in a language. These rules are written using non-terminals (phrase and clause categories) and terminals (words of the language). A word matches a terminal if it has the same part of speech. The words used in the exercises about 100 in all stored in the lexicon along with their attributes (part of speech, number, gender, etc.). Each rule defines the structure of a non-terminal as a combination of terminals and non-terminals. Figure 4 lists the grammar for the exercises handled by our modules. The terminals are in italics. The first three rules define the grammatical sentences in a small subset of elementary French. The first rule expresses the fact that a grammatical sentence in the grammar can consist of a terminal followed by a set of non-terminals. In this case, the terminal is called 'question', which we use to represent "est-ce que" in the lexicon. The non-terminals are 'np' (noun-phrase) and 'vp' (verb-phrase). These are defined by other rules in the grammar. There are, for example, a number of rules which can define 'np', any one of which will produce a grammatical sentence. For example, the rule np(g,n,p) --> pronoun (G,N,P) means that an 'np' can be a pronoun. In a similar manner, other rules indicate that an 'np' can also be a proper noun or an article followed by a noun. The braces immediately following a rule indicate the additional constraints that also apply to the rule. The first rule in the grammar has the constraint {N 1 =N 2,P 1 =P 2 } which stipulates that the 'np' and the 'vp' must agree in number (N 1 =N 2 ) and person (P 1 =P 2 ). A similar constraint exists in the rule npl(g,n,p)--> det(g 1,N 1,P), n(g 2,N 2,P) {G 1 =G 2, N 1 =N 2 } where the determiner and the noun must be of the same number and gender. CALICO Journal, Volume 9 Number 1 13

6 Figure 4. The Grammar s--> question, np(g,n,p), vp(n 2,P 2 ) {N 1 =N 2,P 1 =P 2 } s--> adverb, np(g,n 1,P 1 ), vp(n 2,P 2 ) {N 1 =N 2,P 1 =P 2 } s--> np(g,n 1,P 1 ), vp(n 2,p 2 ) {N 1 =N 2,P 1 =P 2 } np(g,n,p)--> pronoun(g,n,p) np(g,plural,p)--> npl(g,n,p), conj, npl(g,n,p) np(g,n,p)--> npl(g,n,p) npl(g,n,p)--> proper-noun(g,n,p) npl(g,n,p)--> det (G 1,N 1,P), n(g 2,N 2,P) {G 1 =G 2,N 1 =N 2 } vp(n,p)--> v(n,p), complements vp(n,p)--> v(n,p)(vowel Rule), v(n,p), neg2, complements complements--> prep, proper_noun complements--> int, adv complements--> adv complements--> n In the rule vp(n,p)--> neg1(vowel Rule), vp(n,p), neg2, complements, 'Vowel Rule' refers to the use of 'n' or 'ne' before the verb. 'N' is used if the verb begins with a vowel or a mute 'h' and 'ne' in the other cases. The Lexicon The lexicon contains the list of words used in the exercises along with grammatical information about them. Each word is stored using five slots. The first two slots contain the word and its part of speech. The remaining three slots contain the gender, number and person, when applicable. The pronoun 'il' and the proper nom 'Jean-Pierre' for example, are listed as follows: il", pronoun, MASC, SING, 3, Jean-Pierre", proper-noun, MASC, SING, 3. CALICO Journal, Volume 9 Number 1 14

7 Verbs are listed differently. At present we only deal with verbs that do not involve stem changes. The lexicon only contains the root of the verb; for example, there is an entry "parl", verb,-,-,-. There is also a separate dictionary of verb endings which lists each possible ending along with the corresponding number and person, as shown below: e", SING, 1,-,-, "es", SING, 2,-,-, e", SING, 3,-,-, eons", PLUR, 1, G,-, ons, PLUR, 1,-,-, ez", PLUR, 2,-,-, "ent", PLUR, 3,-,-, As we expand the lessons, the lexicon will have to contain additional information. The information on a verb, for example, will specify the past participle, the auxiliary it uses in compound tenses, and the kinds of complements it allows (a direct -object, an indirect object, an infinitive preceded by a preposition). The Parser The parser uses the grammar to assign a grammatical structure to the question and the student's actual response. If the student's answer is not a valid sentence, it tries to parse as much of the sentence as possible and identify the errors. Let us look at an example of how the parser works. Suppose the sentence is "Elle ne parle pas beaucoup. " The parser is a top-down parser it starts from the rules defining a sentence, namely 1. s-- > question, np(g,n1,p1), vp(n 2,P 2 ) {N 1 =N 2,P 1 =P 2 }, 2. s-- > adverb, np(g,n 1,P 1 ), vp(n 2,P 2 ) {N 1 =N 2,P 1, =P 2 }, 3. s--> np(g,n 1,P 1 ), vp(n 2,P 2 ) {N 1 =N 2,P 1 =P 2 } Rule 1 says that the sentence may start with the terminal 'question'. After consulting the lexicon which contains information on each word, the parser determines that the rule is not applicable because the first word is not a question. Nor is rule 2 applicable. The parser then applies rule 3 and tries to recognize a noun phrase and a verb phrase. A noun phrase must conform to one of the rules 4, 5 or 6. These are: CALICO Journal, Volume 9 Number 1 15

8 4. np(g,n,p)- > pronoun (G,N,P), 5. np(g,plural,p)- > np1 (G,N,P), conj, np1(g,n,p), 6. np(g,n,p)- > np1(g,n,p). Rule 4 requires the word to be a pronoun, as is the case here. Thus the parser records the fact that the noun phrase is the third person feminine singular pronoun elle. Next it tries to parse a verb phrase. Rules 9 and 10 are relevant here: 9. vp(n,p)- > v(n,p), complements, 10. vp(n,p)-- > neg1(vowel Rule), v(n,p), neg2, complements. Rule 9 requires a verb followed by a complement. The parser checks the next word ("ne") in the lexicon. It is not a verb. It therefore goes to the next possible form of a verb phrase: the leading negative, a verb, the trailing negative and complements. The "ne is recognized, as is the verb "parle " (whose person and number indeed match that of the noun phrase), as well as the trailing negative "pas". Finally, using rules 11-14, which are: 11. complements- > prep, proper_noun, 12. complements--> int, adv, 13. complements-- > adv, 14. complements-- > n, "beaucoup" is recognized as an adverb. To the extent that rule 3 for the structure of a sentence is satisfied and all the words in the sentence have been used, the parse has been successful. Each part of the sentence has been classified, and the overall structure is represented by the following tree. Sentence np vp pronoun neg1 verb neg2 adverb Elle ne parle pas beaucoup What happens if the parser encounters an incorrect student response? It attempts to assign a structure to as much of the sentence as Usable and to flag as an error the incorrect parts. The way the negative is handled illustrates the point. Negatives in French have two parts; an error cannot therefore be confirmed until the second part has been reached. If the sentence includes the first part of the negative 'ne', but pas' is missing, the parser puts out an error flag when it CALICO Journal, Volume 9 Number 1 16

9 reaches the position where 'pas' should be. If, on the other hand, 'ne' is missing, the parser continues to parse to see if there is a 'pas'; only when it finds 'pas' doe it set the error code for the 'ne'. Let us now look at a complete example of an incorrect answer. Assume that the student has responded "Il n'parlent beaucoup. " The parser starts with rules 1-3 defining a sentence and proceeds much as in the example. It chooses rule 3 for the definition, and uses rule 4 to recognize the pronoun Il" as the noun phrase. In trying to parse the verb phrase, the presence of the negative "n' " dictates rule 10. The next word, parlent, does not start with a vowel, so an error is recorded. "Parlent" is recognized as a verb, but the number (plural) of the ending does not match that of the subject ("il -singular) and another error is recorded. The next word, according to rule 10, must be the trailing negative. It is not, so yet another error is recorded. Finally, just as in the previous example, rule 13 is used to classify the adverb "beaucoup" as a valid complement. The parser bas thus built the following parse tree and signaled the appropriate errors. Sentence np vp pronoun neg1 verb -adverb il n parlent beaucoup If the student were responding to the question "Est-ce que Monique parle beaucoup", the student's response should contain the feminine singular pronoun "elle". But this is not a syntax error and cannot be detected by the parser. Such context errors are detected by the diagnostic component described in the next section. The example above illustrates a few of the errors detected by the parser. A complete list of the errors detected in the exercise on the negative appears in Figure 5. It should be noted that the parser only assigns a structure to the correct answer in an indirect manner. The parse tree of the correct answer is generated by making substitutions to the parse tree of the question. These are done using simple rules: 1. Drop the question marker and insert "non in the sentence. 2. a. If the subject is a noun, replace it with a pronoun of the same number and gender. b. If the subject is a first person pronoun, change it to second person or vice versa. 3. If the person of the pronoun has been changed, adjust the ending of the verb. In thesecondmodule, for example, the student is asked to answer questions in the negative. Assume that the question is "Est-ce que tu travailles beaucoup?". The program first removes the question marker "est-ce que" and substitutes the adverb "Non" to make the sentence negative. Then the first person pronoun je" is substituted for the second person pronoun tu", and the verb is changed to "travaille" to agree with the new subject. The exercise requires a negative answer so the two parts of the negative are added to the response. In the example, the sentence is CALICO Journal, Volume 9 Number 1 17

10 made negative by adding ne" before the verb "travaille and "pas after. Finally, the remainder of the question is copied to the response, i.e. beaucoup is copied to the end of the sentence to produce the correct response Non, je ne travaille pas beaucoup." Parsing New Material In order to make sure that new exercise set items can be handled by the parser, our program checks to make sure that the words used in the sentence are in the dictionary and that the sentence is compatible with the limited capabilities of the grammar. The entry module used to create or augment an exercise file first ensures that each word is in the dictionary. If it is not, it asks the user for the necessary information about the word (part-of-speech, gender, etc.). It then attempts to parse the sentence. If the parse fails, the sentence is clearly unsuitable; otherwise the dictionary is updated and the sentence is included in the exercise file. B. The Diagnostic Component The diagnostic component detects errors the parser cannot identify. More specifically, it recognizes context errors and exercise-related errors. Context errors are those where the student's response, although syntactically correct, is not an appropriate answer to the question (see part A of Figure 6). For instance, the pronoun substitute for the proper noun "Janine " must be " elle", the 3rd person feminine singular pronoun; a question asked with "tu", a 2nd person singular pronoun, requires "je", a 1st person singular pronoun, in the response. The diagnostic component checks the student s answer for both types of context errors. Other context errors are more subtle. Assume the student's answer is "Non, tu ne parles pas espagnol " to the question " Est-ce que tu parles espagnol? ". The correct answer is "Non, je ne parle pas espagnol." The parser will not detect an error in the student's response because it is a syntactically correct sentence. Yet, because the student bas responded with the wrong subject pronoun, an error is detected by the diagnostic component: the response is wrong in this context. The tutor later asks the student to use the right subject pronoun "je". Verb endings in French, however, are highly inflected, so a change in the subject may require a modification in the verb. Once the student bas corrected the subject pronoun, there is an error in the verb ending, which ought to be "e", not "es". The diagnostic component detects this error by matching the verb form in the student's answer with the verb in the correct answer. Unlike the errors noted above, other errors detected by the diagnostic component are exercise specific. For example, if the student does not substitute, a subject-pronoun for the noun or answer CALICO Journal, Volume 9 Number 1 18

11 Figure 5. Errors detected by the parser in the negative as required by the exercise, the diagnostic component detects the error. It does so by checking the parse tree of the student's answer to see if the response is negative and does contain a pronoun as subject. These exercise-related errors cannot be detected by the parser. The number of exercise specific errors is quite small relative to the total number of errors and we would guess that the proportion will not increase considerably. In the tutor, the exercise related errors listed in part B of Figure 6 are handled separately from the others and can be easily deactivated when not required by the exercise. The diagnostic component does its work by using the parse trees of the original question, the correct answer and the student's response. Information about the sentence and about various errors mentioned above are passed on to the tutor using a set of flags. Figure 6 contains a complete list of errors the system can diagnose. C. The Tutor The tutor is a rule-based system that asks the student questions about errors detected by the parsing and diagnostic components. It attempts to model the way in which a teacher would respond when actually tutoring a student in French. The order in which the tutor handles the errors is determined by a built in priority list. Each item on this list corresponds to a group of errors. The priority list for the exercises on the negative is shown below. CALICO Journal, Volume 9 Number 1 19

12 (1) Pronoun/Exercise: exercise type errors in the subject-pronoun, (error B.11 from Figure 6) (2) Pronoun: syntax or context errors in the subject-pronoun, (errors 1-6 from Figure 6 and 1) (3) Verb: syntax or context errors in the verb, (errors 2-8 from Figure 5 and 8 from Figure 6) (4) Negative: syntax errors in the negative, (errors 9-12 from Figure 5) (5) Negative/Exercise: exercise type errors in the negative, (en-or B. 12 from Figure 6) (6) Answer: prints the correct answer. It will be noted that errors are categorized by part of speech, and within each part of speech, the exercise-type errors are separated from the syntax and context errors. This facilitates the changes CALICO Journal, Volume 9 Number 1 20

13 needed to handle exercises of different types. Thus, the only difference between the module which requires the student to respond in the negative and the one which does not is the presence or absence of Negative/Exercise on the list. The tutor-calling routine is rather straightforward. It first checks to see if the student s answer is correct and, if it is, prints an appropriate message. If the answer is not correct, it sequentially takes each item on the priority list and calls the corresponding function. The last item on the priority list, Answer, calls a function which prints the correct answer. Each tutorial functions contain a sequence of clauses ( if statements), each related to an error. Each statement contains the actions taken by the tutor when that error occurs. If there are no errors of the type handled by the function, control returns to the main routine. The negative in French, for example, requires ne before the verb and pas after the verb. In addition, if ne is followed by a word beginning with a vowel, n is used. So, four errors are possible, three with ne and one with pas. Ne can be missing or used when the next word begins with a vowel or n used when the next word begins with a consonant, or pas can be missing. The function therefore has four if statements each related to one of these errors. The statements contain the actions taken by the tutor when the error occurs. When a function is called and an error triggers one of its clauses, the words related to the error CALICO Journal, Volume 9 Number 1 21

14 are looked up in the parse tree. The student is then asked specific questions about the error. All the functions contain similar conditions and actions for errors. Figure 7 contains a sample of the procedure for the verb-errors function. If the question to the student is Est-ce que tu voyages beaucoup? and the student has responded Non, je ne voyages pas beaucoup., the parser will signal that the verb ending is wrong and the code in Figure 7 from the tutor will be triggered. The program first traverses the parse tree of the correct answer to find the subject je and the verb of the sentence voyage. A message is then printed on the screen telling the student that the right verb has been used, but that there is a problem with the ending of the verb. The program then points out to the student that the subject is je and that the root of the verb that the student has correctly used is voyag, and asks what the right ending should be. After reading the student s answer, the program tries CALICO Journal, Volume 9 Number 1 22

15 to match it to the correct answer e. If they match, a message indicating that the student is right is printed; otherwise the student is given the correct form. Sometimes more than one question is asked of the student. A clause in the pronoun errors function shown in Figure 8 serves as an illustration. Assume the question is Est-ce que Bob et Monique parlent espagnol? and that the student has answered with Non, il ne parlent pas espagnol. This pronoun-error clause is triggered when the third person subject pronoun the student has used is of the wrong number, as in the example above. The program first finds the subject of the sentence Bob et Monique in the parse tree of the question. It then asks the student if the subject is singular or plural. IV. Conclusion The three component design (parsing, diagnostics and tutoring) allows instruction which is specific to the student s errors and models the behavior of a human instructor. The parsing and diagnostic components provide the detailed information about the syntax, context and exerciserelated errors, as well as the syntactic information contained in the parse trees which are crucial for creating the instructor-like dialogue in the tutor. Furthermore, the three part design allows the program to be modular: separate functions are identified and isolated and hence can be modified with relative ease. The design can be generalized (within the limited scope of elementary French) to other types of exercises. For each type of exercise, one has to classify the possible errors into three categories (syntactic, contextual and exercise related). These have to be grouped and the groups prioritized for tutoring. Finally, the corresponding tutoring rules have to be tailored to the errors. We need, however, to make several improvements. The grammar can be enlarged to handle a larger variety of sentences. In addition the lexicon and the verb morphology are very limited and need to be expanded. Finally, the diagnostic strategy does not handle certain errors commonly made by students, such as misspellings and misplaced words. We are developing a scheme to deal with some of these errors. Still, we have taken a modest step towards a system that would mimic human tutoring. CALICO Journal, Volume 9 Number 1 23

16 REFERENCES Allen, James Natural Language Understanding. Menlo Park, CA: Benjamin/Cummings. Bailin, Alan and Lori Levin, eds Intelligent Computer-Assisted Language Instruction. A special issue of Computers and the Humanities 23, 1, Bailin, Alan and Philip Thomson The Use of Natural Language Processing in Computer- Assisted Language Instruction. Computers and the Humanities 22, Kearsley, Greg, ed Artificial Intelligence and Instruction: Applications and Methods. Reading, MA: AddisonWesley. Pereira, Fernando C. N. and Stuart M. Shieber Prolog and Natural-Language Analysis. Stanford, CA: Center for the Study of Language and Information. Polson, Martha C. and J. Jeffrey Richardson, eds Intelligent Tutoring Systems: Lessons Learned. Hillsdale, NJ: Lawrence Erlbaum. Sanders, Alton F. and Ruth H. Sanders Syntactic Parsing: A Survey. Computers and the Humanities 23, Wenger, Etienne Artificial Intelligence and Tutoring Systems: Computational and Cognitive Approaches to the Communication of Knowledge. Los Altos, CA: Morgan Kaufmann. Winograd, Terry Language as a Cognitive Process. Vol. 1 (Syntax). Reading, MA: Addison- Wesley. AUTHORS BIODATA Gilles Labrie is an Associate Professor of French at Central Michigan University. His present research interests are in computer applications to elementary and intermediate language instruction. L.P.S. Singh is an Associate Professor of Computer Science at Central Michigan University. His research interests are in the areas of intelligent tutoring systems, parallel computing and databases. CALICO Journal, Volume 9 Number 1 24

17 AUTHORS ADDRESSES Gilles Labrie Department of Foreign Languages, Literatures and Cultures Central Michigan University Mt. Pleasant, MI Bitnet: L.P.S. Singh Department of Computer Science Central Michigan University Mt. Pleasant, MI CALICO Journal, Volume 9 Number 1 25