=Paper=
{{Paper
|id=Vol-2481/paper2
|storemode=property
|title=Prerequisite or Not Prerequisite? That’s the Problem! An NLP-based Approach for Concept Prerequisite Learning
|pdfUrl=https://ceur-ws.org/Vol-2481/paper2.pdf
|volume=Vol-2481
|authors=Chiara Alzetta,Alessio Miaschi,Giovanni Adorni,Felice Dell'Orletta,Frosina Koceva,Samuele Passalacqua,Ilaria Torre
|dblpUrl=https://dblp.org/rec/conf/clic-it/AlzettaMADKP019
}}
==Prerequisite or Not Prerequisite? That’s the Problem! An NLP-based Approach for Concept Prerequisite Learning==
Prerequisite or Not Prerequisite? That’s the Problem! An NLP-based Approach for Concept Prerequisites Learning Chiara Alzetta• , Alessio Miaschi? , Giovanni Adorni• , Felice Dell’Orletta , Frosina Koceva• , Samuele Passalacqua • , Ilaria Torre• • DIBRIS, Università degli Studi di Genova, ? Dipartimento di Informatica, Università di Pisa, Istituto di Linguistica Computazionale “Antonio Zampolli”, Pisa - ItaliaNLP Lab {chiara.alzetta,frosina.koceva}@edu.unige.it, alessio.miaschi@phd.unipi.it, samuele.passalacqua@dibris.unige.it, {ilaria.torre,adorni}@unige.it, felice.dellorletta@ilc.cnr.it Abstract 2009; Kurilovas et al., 2015; Almasri et al., 2019). The most fundamental issue behind this task is the English. This paper presents a method need to understand how educational concepts are for prerequisite learning classification be- pedagogically related to each other: what infor- tween educational concepts. The proposed mation one has to study/know first in order to un- system was developed by adapting a clas- derstand a given topic. In this paper we focus on sification algorithm designed for sequenc- such relations, i.e. prerequisite relations, between ing Learning Objects to the task of order- educational concepts of a textbook in English and ing concepts from a computer science text- we present a method for their automatic identifi- book. In order to apply the system to the cation. Here, we define concepts all the relevant new task, for each concept we automati- topics extracted from the textbook and we repre- cally created a learning unit from the text- sent them as single or multi word terms. book using two criteria based on concept Automatic prerequisite extraction is a task occurrences and burst intervals. Results deeply rooted in the field of education, whose re- are promising and suggest that further im- sults can be easily integrated in many different provements could highly benefit the re- contexts, such as curriculum planning (Agrawal et sults.1 al., 2016), course sequencing (Vuong et al., 2011), Italiano. Il presente articolo descrive una reading list generation (Gordon et al., 2017), au- stategia per l’identificazione di prerequi- tomatic assessment (Wang and Liu, 2016), do- siti fra concetti didattici. Il sistema pro- main ontology construction (Zouaq et al., 2007; posto è stato realizzato adattando un al- Larranaga et al., 2014) and automatic educational goritmo per ordinamento di Learning Ob- content creation (Lu et al., 2019). Several meth- jects al compito di ordinamento di concetti ods have been devised to extract prerequisite rela- estratti da un libro di testo di informat- tions (Liang et al., 2015; Pan et al., 2017a; Liang et ica. Per adeguare il sistema al nuovo sce- al., 2018b), however they were mainly focused on nario, per ogni concetto stata automatica- educational materials already enriched with some mente creata una unità di apprendimento sort of explicit relations, such as Wikipedia pages, a partire dal libro di testo selezionando i course materials or learning objects (LOs). More contenuti sulla base di due differenti cri- challenging is identifying prerequisites when no teri: basandosi sull’occorrenza del con- such relations are given and textual content is the cetto e sugli intervalli di burst. I risultati only available resource. sono promettenti e lasciano intuire la pos- In 2019, we proposed two methods to iden- sibilità di ulteriori miglioramenti. tify prerequisite relations between concepts with- out using external knowledge or even pre–defined relations. The former method (Adorni et al., 2019) 1 Introduction is based on burst analysis and temporal reasoning Personalised learning paths creation is an active on concepts occurrence, while the latter (Miaschi research topic in the field of education (Chen, et al., 2019) uses deep learning for learning object ordering. Both these methods extract prerequisite 1 Copyright c 2019 for this paper by its authors. Use per- mitted under Creative Commons License Attribution 4.0 In- relations form textual educational materials with- ternational (CC BY 4.0). out using any form of structured information. In this work, we adapt the system for learning pairs generated from the combination of selected object ordering described in Miaschi et al. (2019) concepts (Chaplot et al., 2016; Wang et al., 2016; to the task of sequencing concepts in a textbook Li et al., 2019) or a random sample of that set according to their prerequisite relations. For train- (Pan et al., 2017b; Gordon et al., 2017; Gasparetti ing and testing our system we relied on a new ver- et al., 2018). The dataset presented by Wang et sion of PRET (Alzetta et al., 2018), a gold dataset al. (2016) is the one we consider most closely re- manually annotated with prerequisite relations be- lated to ours, since it shows prerequisite relations tween educational concepts. Moreover, since the between relevant concepts extracted from a text- classifier was designed to acquire learning objects book. However, in their dataset a matching with a as input, we automatically created a learning unit2 Wikipedia page was a strict requirement for con- for each concept according to two different cri- cept selection. Contrary to previous works, we teria: (i) considering all sentences showing an asked experts to build the concept pairs if a prereq- occurrence of the concept, (ii) considering burst uisite relation was observed while reading a text- intervals (Kleinberg, 2003) of each concept ex- book, regardless the existence of a corresponding tracted according to the strategy of Adorni et al. Wikipedia page for the concepts. Hence we al- (2019). lowed for more subjectivity, without restricting ex- The remainder of the paper is organised as fol- perts’ evaluation to a predefined list of items. lows. First, we present related work (Section 2) For what concerns prerequisite learning ap- and the dataset used for the experiments (Section proaches, initial work in this field relied on graph 3). Section 4.1 presents the classifier, while Burst analysis (Vassileva, 1997; Brusilovsky and Vas- analysis is described in Section 4.2 and the experi- sileva, 2002) or, more recently, on link-based met- mental settings in Section 4.3. Results and discus- rics inferred from the Wikipedia graph of hyper- sion are reported in Section 4.4, while error analy- links between pages (Liang et al., 2015). Talukdar sis is illustrated in Section 5. Section 6 concludes and Cohen (2012) made the first attempt to apply the paper. machine learning techniques to prerequisite pre- Our Contribution. In this paper: (i) we use diction: hyperlinks, hierarchical category struc- a deep learning-based approach for prerequisite ture and edits of Wikipedia pages are the features relation extraction between educational concepts of a MaxEnt classifier. Similarly, Gasparetti et al. of a textbook; (ii) we test the impact of creating (2018) use Wikipedia hierarchical category struc- learning units for each concept according to dif- ture and hyperlinks. Similarly to our approach, ferent criteria and without relying on any explicit (Liang et al., 2018a; Liang et al., 2018b) integrated structured information, such as Wikipedia hyper- text–based features for prerequisite learning, but links; (iii) we show the effectiveness of our ap- reported graph–based features as more informa- proach on real educational materials. tive. Contrary to the above methods, we assign a 2 Related Work higher informative value to the textual content re- ferring to a concept and we use this only to extract Datasets annotated with prerequisite relations are the features for the classifier. Moreover, we com- built mainly considering two types of data: course bine the classifier with the burst algorithm (Klein- materials, acquired from MOOCs (Chaplot et al., berg, 2003), which selects the most relevant tex- 2016; Pan et al., 2017a; Pan et al., 2017b; Gas- tual content related to a concept from the tex- paretti et al., 2018; Roy et al., 2018) or university tual material. This choice makes our method suit- websites (Liang et al., 2017; Li et al., 2019), and able for prerequisite learning on educational con- educational materials in a broader sense, such as tents also when structured graph information is not scientific databases (Gordon et al., 2017), learn- available. ing objects (Talukdar and Cohen, 2012; Gasparetti et al., 2018) and textbooks (Wang et al., 2016). 3 Dataset The most common approach for prerequisite an- notation is to ask experts to evaluate all possible For our experiments we relied on a novel version 2 of PRET dataset (Alzetta et al., 2018), PRET 2.0, a Learning unit is meant here as learning content, with no reference to units of learning in curricula and tables of con- dataset manually annotated with prerequisite rela- tent. tion between educational concepts extracted from a chapter of a computer science textbook written in English (Brookshear and Brylow, 2015). In this novel version, five experts were asked to re–annotate the same text indicating any prerequi- site concept of each relevant term appearing in the text. The set of relevant terms was extracted with the same automatic strategy described in Alzetta et al. (2018), but this time the list was manually validated by three experts in order to identify a commonly agreed set of concepts, which resulted in a terminology of 132 concepts. Besides these terms, each expert could independently add new concepts to the terminology when annotating the text if he/she regards them as relevant. Conse- quently, experts produced different sets of concept Figure 1: Method workflow. pairs annotated with prerequisite relations since 221 new concepts were manually added during the annotation process. fication of concept pairs: given a pair of concepts The final gold dataset results from the combina- (A,B), we predict whether or not concept B is a tion of all annotations, thus considering as positive prerequisite of concept A. pairs (i.e. showing a prerequisite relation) all pairs 4.1 Classifier of concepts annotated by at least one expert. The manual annotation resulted in 25 pairs annotated The system used to predict whether or not two by all five experts, 46 annotated by four experts, concepts show a prerequisite relation is the deep 83 by three, 214 by two and 698 by only one an- learning architecture described in Miaschi et al. notator, for a total of 1,066 pairs. (2019). Specifically, we relied on the model 2,349 transitive pairs were also automatically which uses pre-trained word embeddings (WE) generated and added to the dataset: if a prereq- and global features automatically extracted from uisite relation exists between concepts A and B the dataset. and between concepts B and C, we add a posi- The system architecture (see Figure 1) is com- tive relation between A and C to increase the co- posed of two LSTM-based sub-networks with 64 herence of annotation. In order to obtain a bal- units, whose outputs are concatenated and joined anced dataset for training our deep learning sys- with a set of global features. The input of the tem, negative pairs were automatically created by two LSTM-based sub-networks corresponds to the randomly pairing concepts and adding them as pre-trained WE of concept A and B respectively. negative examples if they were missing in the The output layer consists of a single Dense unit dataset. Overall, the final dataset consists of 353 with sigmoid activation function. The pre-trained concepts and 6,768 relations. WE were computed using an English lexicon of 128 dimensions built using the ukWac corpus (Ba- 4 Method and Experiments roni et al., 2009). Global features were devised to extract linguistic information from learning units In this Section we present our approach for of both concepts in a pair, such as mentions to the learning prerequisites between educational con- other concept of the pair or the Jaccard similarity cepts.We trained and tested the same deep learn- between textual contents of the two learning units. ing model on three datasets generated from PRET For the complete list of global features, refer to 2.0 that vary with respect to the criterion used for Miaschi et al. (2019). retrieving textual content of each concept in the dataset. As a result, we were able to study perfor- 4.2 Burst Analysis mance variations of the classifier given different Burst analysis is based on the assumption that a input data. phenomenon might become particularly relevant Task. We tackle the problem of concept prereq- in a certain period along a time series, most likely uisite learning as a task of automatic binary classi- because its occurrence rises above a certain thresh- old. Such periods of increased activity of the phe- Emb. Model F-Score Accuracy Dim. nomenon are called ”burst intervals” and can be 5 73.75 69.65 modelled by means of a two state automaton in Occurrence 10 74.79 70.36 which the phenomenon is in the first state if it has 15 73.7 69.19 30 73.11 67.97 a low occurrence, but then it moves to the second avg 73.84 69.30 state if its occurrence rises above a certain thresh- 5 71.75 65.54 old, and eventually it goes back to the first state Burst 10 73.91 69.49 Intervals 15 72.97 67.77 if its occurrence goes below the threshold (Klein- 30 71.37 65.06 berg, 2003). avg 72.5 66.96 5 73.06 67.8 Given its nature, this kind of analysis is highly Most Relevant 10 72.04 66.52 employed for detecting events from data streams Burst Interval 15 71.58 64.43 (Fung et al., 2005; Takahashi et al., 2012; Klein- 30 71.49 64.48 avg 72.04 65.80 berg, 2016). When applied to textual data – e.g., Baseline 66.66 50 for text clustering (He et al., 2007), summariza- tion (Subasic and Berendt, 2010) or relation ex- Table 1: Classification F-Score and Accuracy val- traction (Yoon et al., 2014; Lee et al., 2015) – the ues for the three models with varying number of linear progression of the text acts as the time se- sentences considered for lexical features. Average ries, hence burst intervals correspond to sequences and baseline values are also reported. of sentences where a given term is particularly rel- evant. In Adorni et al. (2019) burst analysis was criteria: (1) considering all sentences where a cer- used to detect the bursting intervals of concepts tain concept occurs (Occurrence Model); (2) con- along a textbook chapter: for each term, the burst sidering burst intervals for each concept. The lat- algorithm identified a unique or multiple burst in- ter is further divided into two cases depending on tervals of various length (i.e. a different number the appearing order of burst intervals: (i) burst of sentences involved in each interval). Temporal intervals reflect their linear order along the text reasoning (Allen, 1983) was then employed to find (Burst Intervals Model); (ii) burst intervals are re- prerequisite relations between concepts. ordered, having the most relevant burst interval as In this work we use the burst intervals retrieved first (Most Relevant Burst Interval Model). The as described in Adorni et al. (2019) to select rele- most relevant burst interval is defined as the first vant content of the textbook for each concept. Our burst interval that exceeds the average length of intuition is that burst intervals should capture the all the bursts of that concept (Adorni et al., 2019; most informative portions of text for each concept Passalacqua et al., 2019). from the entire textbook content. Note that for The resulting datasets show different learning this experiment we only used the bursts detected unit dimensions: Burst Intervals models produce with the first phase of the algorithm described in learning units with an average length of 534 to- (Adorni et al., 2019), i.e. the temporal reasoning kens, while those considered for the Occurrence is not employed here. Model are smaller, with 250 tokens on average. While global features consider the entire content 4.3 Experimental Settings of the learning unit, for all models WE are com- Since our deep learning model was designed to puted only for the first n sentences. We tried dif- find prerequisite relations between learning ob- ferent length of n: 5, 10, 15 and 30. jects, we had to adapt our classification algorithm Results in terms of F-Score and accuracy were to the task we deal with in this work, namely or- compared against a Zero Rule algorithm baseline. dering concepts from a textbook. To this aim, we created learning units for each concept of PRET 4.4 Experiments Results and Discussion 2.0 dataset and we used them as input for the clas- Results reported in Table 1 show satisfying perfor- sifier. mances of our system that outperforms the base- In order to verify the impact of different input line in all configurations. Best results are obtained data, we tested different strategies for the creation by the Occurrence Model using 10 sentences to of learning units. Hence, content related to each compute lexical features. In general, computing concept was retrieved according to two different the WE on 10 sentences or less allows to obtain better performances in all settings. This could be due to the fact that the definition of a concept and its contextualisation with respect to other concepts are generally discussed by the author of the book when the concept is first mentioned in the text. Thus, sentences containing the first occurrences of the term seem to be the most informative for this task. To assess this hypothesis, we manually in- spected sentences containing the first mention of each concept. The analysis revealed that 36.3% of the observed sentences contained a concept defi- Figure 2: Variation of accuracy values wrt the nition, thus supporting our intuition that the first classifier confidence for pairs labelled as prereq- mention is relevant for concept contextualisation. uisite (P) and non prerequisite (NP) in all models The results obtained using the Burst Interval considering 10 sentences to compute lexical fea- Model are slightly worse, although comparable, tures. probably because, since burst intervals do not nec- essarily capture all the occurrences of a concept, value (i.e. equal to 1) are only 1.21%. in some cases the first mentions could be miss- ing from the learning unit. The lowest scores are predictably those obtained using the Most Rele- vant Burst Interval Model: changing the order of the sentences penalises the system since the tem- poral order often plays an important role when a prerequisite relation is established between two concepts. Several algorithms exploit a time-based strategy for prerequisite extraction relying on the temporal nature of this relation (Sosnovsky et al., 2004; Adorni et al., 2018) and the analysis of hu- man annotations suggests that the direction of this relation (i.e. A is prerequisite of B or vice-versa) tends to be highly correlated with the temporal or- der of the two concepts (Passalacqua et al., 2019). Besides, the most relevant burst is not necessarily the first burst interval for that concept and, for this reason, it could contain less relevant information about the concept and its prerequisites. Interest- ingly, the best results for this model are obtained considering only 5 sentences for computing WE, probably because the system has less chance of observing a lexicon related to other concepts. If we look at the variation of accuracy values Figure 3: Variation of confidence (on top) and ac- with respect to the classifier confidence (see Fig- curacy (on bottom) wrt the agreement value for ure 2), we observe that our system shows an ex- the Occurrence Model (all possible embeddings pected behaviour. In fact, at high confidences cor- length are considered). respond high accuracy scores, while at confidence around .5 (12.66% of dataset pairs) we notice that The graphs in Figure 3 show the variation of the classifier is more unsure of its decision, obtain- confidence and accuracy values with respect to the ing results below the baseline. It should be noted annotators agreement. We report results only for also that the majority of concept pairs (25%) have the Occurrence Model since it is the one that ob- been classified with a confidence value around .6, tained the best scores during classification. As we while the pairs obtaining the highest confidence can see, the concept pairs for which all the annota- tors agree on tend to obtain higher confidence and, requisite relation out of textual educational mate- consequently, the classifier shows the best perfor- rial without using any form of structured informa- mances. The only exception is the model that tion. Nevertheless, further work needs to be done, computes WE using the first 30 sentences, which particularly for improving the performances of our obtains instead the best scores on the pairs anno- system in a out-of-domain scenario, namely using tated by only 3 experts. The reason for this be- concept pairs of a different domain during testing. haviour will be explored in future work. Moreover, it could be useful to investigate the use of transitive relations and to study more accurately 5 Error Analysis their impact on the system’s performance. In addi- tion, in order to identify prerequisite relationships This Section compares the results obtained by the while taking into account different types of rela- three models (i.e. Occurrence, Burst Interval and tions (e.g. transitive ones) it could be interesting to Most Relevant Burst Interval) when considering frame our task as a ranking or multi-classification 10 sentences for computing WE. task rather than a binary classification one. Further The overall number of pairs assigned with a analysis is also required to investigate the effect of wrong label by the classifier is quite similar across using different numbers of sentences for creating each setting: 1,835 pairs for the Occurrences WE. We plan also to explore the impact of using model, 1,923 for the Burst Interval model and temporal reasoning on concept pairs (Adorni et al., 2,089 for the Most Relevant Burst model. More- 2019), which has not been considered in this work. over, we observe that among these pairs more than 80% were classified as “prerequisite”, suggesting that the system overestimates the prerequisite re- References lation, assigning the label also to non–prerequisite pairs. Giovanni Adorni, Felice Dell’Orletta, Frosina Koceva, Ilaria Torre, and Giulia Venturi. 2018. Extracting Focusing the analysis on relations that are an- dependency relations from digital learning content. notated as prerequisites in the dataset, we ob- In Italian Research Conference on Digital Libraries, serve how their prediction varies across mod- pages 114–119. Springer. els. 126 pairs were assigned with a wrong “non- Giovanni Adorni, Chiara Alzetta, Frosina Koceva, prerequisite” label by all models showing similar Samuele Passalacqua, and Ilaria Torre. 2019. 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