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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Towards eficient scoring of student-generated long-form analogies in STEM</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Thilini Wijesiriwardene</string-name>
          <email>thilini@sc.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Ruwan Wickramarachchi</string-name>
          <email>ruwan@email.sc.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Valerie L. Shalin</string-name>
          <email>valerie.shalin@wright.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Amit P. Sheth</string-name>
          <email>amit@sc.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>AI Institute, University of South Carolina</institution>
          ,
          <addr-line>Columbia, SC</addr-line>
          ,
          <country country="US">USA</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Department of Psychology, Wright State University</institution>
          ,
          <addr-line>Dayton, OH</addr-line>
          ,
          <country country="US">USA</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Switching from an analogy pedagogy based on comprehension to analogy pedagogy based on production raises an impractical manual analogy scoring problem. Conventional symbol-matching approaches to computational analogy evaluation focus on positive cases, and challenge computational feasibility. This work presents the Discriminative Analogy Features (DAF) pipeline to identify the discriminative features of strong and weak long-form text analogies. We introduce four feature categories (semantic, syntactic, sentiment, and statistical) used with supervised vector-based learning methods to discriminate between strong and weak analogies. Using a modestly sized vector of engineered features with SVM attains a 0.67 macro F1 score. While a semantic feature is the most discriminative, out of the top 15 discriminative features, most are syntactic. Combining this engineered features with an ELMo-generated embedding still improves classification relative to an embedding alone. While an unsupervised K-Means clustering-based approach falls short, similar hints of improvement appear when inputs include the engineered features used in supervised learning.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Descriptive analogies</kwd>
        <kwd>Analogical features</kwd>
        <kwd>Analogy scoring</kwd>
        <kwd>Long-form analogies</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Analogical reasoning relies on the ability to draw on the relational similarities between two
systems of objects in diferent contexts [
        <xref ref-type="bibr" rid="ref1 ref2 ref3">1, 2, 3</xref>
        ]. Analogies appear in several disciplines such as
engineering design, scientific reasoning, and often in STEM education. However, the dominant
pedagogical paradigm requires students to comprehend curated analogies. In this work, we
are focusing on the evaluation of student-generated analogies in their first undergraduate
biochemistry course.
      </p>
      <p>
        Problem sets, specifically created to explore the underlying mechanisms of analogical
reasoning, consist of visual and verbal analogies [
        <xref ref-type="bibr" rid="ref4 ref5">4, 5</xref>
        ]. Verbal analogies have two primary forms;
analogical proportions and long-form analogies. Analogical proportions follow a four-term
format such as "A to B as to C to D" or A:B::C:D [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ]. Recent work on computational analogy
making focuses on analogical proportions [
        <xref ref-type="bibr" rid="ref7 ref8 ref9">7, 8, 9</xref>
        ]. Our interest here lies in long-form analogies
consisting of a narrative/ description of a target unfamiliar situation/ system (for the context
or lesson to be learned) using several sentences and a familiar source (base) [
        <xref ref-type="bibr" rid="ref10 ref3">10, 3</xref>
        ]. While the
objects across the two descriptions difer, they employ similar relations between these objects.
An example of a well-known long-form analogy is between the solar system (source) and the
Rutherford-Bohr model of the atom (target) [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ] where small objects revolving around a large
central object provide relational similarity with the target. The solar system and the atom can
each be described using several sentences. Parallels between these two systems can then be
drawn, making the two descriptions analogous.
      </p>
      <p>
        The atom-solar system analogy exemplifies the curated analogies in STEM textbooks. [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ] has
developed algorithms for evaluating correct or slightly incorrect long-form analogies. In [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ]
we solicited analogies from STEM students, with the expectation, relative to a comprehension
exercise, that analogy production is both more engaging and allows students to employ existing
familiar knowledge to scafold the acquisition of new knowledge. No matter how pedagogically
successful, manual scoring is impractical for an analogy production pedagogy. Production
pedagogy elevates an analogy scoring problem for computational solution.
      </p>
      <p>We aim to identify discriminative features between strong and weak, long-form student
generated verbal analogies collected in a college biochemistry class (see Section 2.1) to support
eficient computational scoring. To this end, we develop the Discriminative Analogy Features
(DAF) pipeline.</p>
      <p>We use a long-form analogy dataset, instructor-graded as strong or weak. We explore both
supervised and unsupervised learning classifiers using vectors based on embeddings, engineered
features and both. Given manually annotated data for a supervised learning classifier (i.e. SVM),
we identify the discriminative features of strong and weak analogies.</p>
      <p>We introduce DAF, a pipeline to identify the discriminative features of strong and weak
analogies. We also introduce four feature categories – semantic, syntactic, sentiment, and
statistical used in supervised learning to discriminate between strong and weak analogies.
We show that “unique attribute count”, a semantic feature, is the most discriminative when
identifying between strong and weak analogies. Out of the top 15 discriminative features, most
are syntactic. Unsupervised learning is unable to obtain comparable success, though it slightly
improves with features corresponding to the above categories.</p>
      <p>The rest of this paper is organized as follows: Section 2 introduces and describes the DAF
pipeline and identifies the discriminative features. Section 3 presents the discussion with
ifndings, insights, limitations, and future work subsections. Section 4 concludes the paper.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Discriminative Analogy Features (DAF) Pipeline</title>
      <p>To identify discriminative features, we introduce the pipeline illustrated in Figure 1. In the
subsequent subsections, we describe each pipeline component.</p>
      <p>Dataset &amp; Input
Strong Analogy with</p>
      <p>X Sentences</p>
      <p>X strong sentence</p>
      <p>analogies
Analogy sentence
Dataset (N = X+Y)</p>
      <p>Single
sentence
Weak Analogy with</p>
      <p>Y Sentences</p>
      <p>Y weak sentence</p>
      <p>analogies</p>
      <p>Analysis
— Macro averaged Precision/Recall/F1-Score based</p>
      <p>analysis of SVM classification
— Rand-index-based analysis of K-means clustering
Analogy Processing</p>
      <p>Supervised Learning
SVM-based classification
Features:
— Semantic-based
— Sentiment-based
— Syntactic-based
— Statistical-based
Unsupervised Learning</p>
      <p>K-Means Clustering
Features:
— ELMo embeddings
— CNNB Embeddings
— Engineered features (EF)
— ELMo embeddings + EF
— CNNB embeddings + EF</p>
      <sec id="sec-2-1">
        <title>2.1. Dataset and Input</title>
        <p>The dataset used in this work was drawn from 500 student-created analogies, collected in a
college classroom. An instructor explained a process in the domain of biochemistry, e.g.,
Glycolysis (source analogy), and requested students to construct a scenario analogous to the explained
process from a domain of their choice (target analogy). The instructor then evaluated 31
studentgenerated analogous scenarios as a strong or weak analogy based on its correspondence to the
Biochemistry concept. A strong analogy corresponds well with the target analogy, and a weak
analogy minimally corresponds with the target analogy. To increase the size of the 31 exemplar
data set from the original we split each analogy into its constituent sentences, generating a data
set of 526 strong exemplars and 140 weak exemplars. Each constituent sentence of an analogy
falls into the same annotation category as the original analogy. Ergo, the initial input to the DAF
pipeline is a sentence. This work does not distinguish between the analogy’s target domains
(Enzyme Kinetics and Glycolysis). Table 1 presents the summarized statistics of the dataset.</p>
      </sec>
      <sec id="sec-2-2">
        <title>2.2. Input Processing</title>
        <p>Sentences were processed and used as inputs to a Support Vector Machine (SVM) classifier
(supervised learning) and K-means clustering (unsupervised learning) separately. In the following
section we briefly review the background of input processing techniques, learning methods and
implementation details.</p>
        <sec id="sec-2-2-1">
          <title>2.2.1. Background</title>
          <p>
            SVM is a supervised learning technique that creates functions to map inputs to pre-existing
annotations [
            <xref ref-type="bibr" rid="ref14">14</xref>
            ]. SVM is an easy-to-interpret classifier providing competitive performance in
classification, regression, and outlier detection tasks [
            <xref ref-type="bibr" rid="ref15">15</xref>
            ]. The following paragraphs detail the
background of four feature groups of interest here.
          </p>
          <p>
            The obviously relevant features are semantic. Abstract Meaning Representation (AMR) is a
semantic representation language that expresses a sentence’s logical meaning by converting it
to a rooted, directed, acyclic, edge-labeled, and leaf-labeled graph. [
            <xref ref-type="bibr" rid="ref16">16</xref>
            ]. To abstract away from
syntactic idiosyncrasies, AMR assigns the same AMR graph to sentences with the same meaning.
Nodes of an AMR graph are labeled as concepts, edges as relations, and concept properties as
attributes. Concepts are either English words, PropBank framesets [
            <xref ref-type="bibr" rid="ref17">17</xref>
            ] or special keywords.
There are approximately 100 relations [
            <xref ref-type="bibr" rid="ref16">16</xref>
            ]. AMR is used as a semantic representation of text
in several NLP tasks such as summarization [
            <xref ref-type="bibr" rid="ref18">18</xref>
            ], machine comprehension [
            <xref ref-type="bibr" rid="ref19">19</xref>
            ], and event
extraction [
            <xref ref-type="bibr" rid="ref20 ref21">20, 21</xref>
            ]. In this work we use AMR representations to extract concepts, relations and
attributes present in sentence analogies. Figure 2 illustrates the AMR for a sentence from the
dataset.
          </p>
          <p>
            Sentiment-based features potentially reveal student engagement. Sentiment analysis aims to
identify emotional or afective tendencies in user-generated content such as tweets, product
reviews, and feedback [
            <xref ref-type="bibr" rid="ref22">22</xref>
            ]. Subjectivity detection and polarity determination are two common
tasks in sentiment analysis [
            <xref ref-type="bibr" rid="ref23">23</xref>
            ]. Subjectivity quantifies the personal opinions versus factual
information contained in the text. High subjectivity indicates the text contains more personal
opinions compared to factual information [
            <xref ref-type="bibr" rid="ref23">23</xref>
            ]. Polarity describes the sentiment of a piece of
text as positive, negative, or neutral [
            <xref ref-type="bibr" rid="ref22">22</xref>
            ].
          </p>
          <p>
            We extract three groups of syntactic features. The first feature group is Part of Speech (POS),
a grammatical classification of the word types in a sentence. These POS tags commonly include
nouns, verbs, adjectives, etc. [
            <xref ref-type="bibr" rid="ref24">24</xref>
            ]. Named Entities Recognition (NER), the second feature group,
is used to identify occurrences of named entities such as people, organizations, times, and
locations in a sentence [
            <xref ref-type="bibr" rid="ref25">25</xref>
            ]. The third feature group is sentence type. Sentences in the dataset
are identified as complex or compound sentences and simple sentences. In linguistics, complex
sentences are sentences with two or more clauses connected with a subordinate conjunction.
Simple sentences contain one independent clause [
            <xref ref-type="bibr" rid="ref26">26</xref>
            ].
          </p>
          <p>We use four routine and straightforward statistical features, word count, character count, the
average word length of a sentence (character count/ word count), and the number of unique
words in a sentence.</p>
          <p>
            K-means is a non-deterministic, iterative, and unsupervised machine learning technique
to produce clusters from data [
            <xref ref-type="bibr" rid="ref27">27</xref>
            ]. Unsupervised learning here serves as both a baseline for
comparison with supervised learning results, and as a long term goal in itself, independent of
any manual annotation. In the simplest test, we converted the input sentences to embeddings
and cluster them using K-means clustering. Sentence embeddings were created using two
techniques, context-based Embeddings from Language Models (ELMo) and
knowledge-graphbased ConceptNet Numberbatch (CNNB). The following two paragraphs give a brief overview
of these two embedding techniques.
          </p>
          <p>
            ELMo embeddings are deep, contextualized representations of words computed using a
twolayer bidirectional language model (biLM), which is pretrained on a large text corpus [
            <xref ref-type="bibr" rid="ref28">28</xref>
            ]. ELMo
is robust in creating embeddings for out-of-vocabulary (OOV) words because it incorporates
subword and character-level information when creating embeddings. Handling OOV words
is particularly important in this work as most of the sentences often contain domain-specific
keywords such as “Glucose-6-p", “DHP", “GAP" which can fall into the OOV category. ELMo
sentence vectors are 1024-dimensional.
          </p>
          <p>
            ConceptNet is a semantic network of knowledge about word meanings [
            <xref ref-type="bibr" rid="ref29">29</xref>
            ]. CNNB
embeddings [
            <xref ref-type="bibr" rid="ref30">30</xref>
            ] are semantic word vectors created by encoding the knowledge in ConceptNet [
            <xref ref-type="bibr" rid="ref29">29</xref>
            ].
ConceptNet Numberbatch sentence embeddings are produced by taking the mean of single word
embeddings in a sentence. CNNB sentence vectors are 300-dimensional. CNNB embeddings
are not as robust as ELMo embeddings when handling OOV words, yet the percentage of OOV
words in the current dataset is rather small (6%). Hence we use CNNB as the second embedding
technique to create sentence embeddings.
          </p>
        </sec>
        <sec id="sec-2-2-2">
          <title>2.2.2. Implementation Details</title>
          <p>
            We use Pandas DataFrames [
            <xref ref-type="bibr" rid="ref31">31</xref>
            ] to process and manipulate the sentence features. We also
used other external libraries used in the extraction of sentence features as follows. To extract
semantic features, the sentences are sent through a transition-based AMR parser named CAMR
[
            <xref ref-type="bibr" rid="ref32">32</xref>
            ]. Textblob [
            <xref ref-type="bibr" rid="ref33">33</xref>
            ] is used to assess the subjectivity and polarity scores of the sentences. POS tag
and NER-related features (in syntactic features category) are extracted using spaCy 1. Matplotlib
2 and seaborn 3 are used for the visualizations.
          </p>
          <p>ConceptNet Numberbatch embeddings are static representations for words available publicly
4. ELMo sentence embeddings were created using the model available at Tensorflow Hub 5.</p>
        </sec>
      </sec>
      <sec id="sec-2-3">
        <title>2.3. Analysis</title>
        <p>In the following sections, we look at semantic, sentiment-based, syntactic, and statistical feature
distributions for strong and weak analogies. We then compare the performances of an SVM
classifier and K-means clustering.</p>
        <p>Figure 3 illustrates the distributions of counts of concepts, relations, attributes, unique
concepts, unique relations, and unique attributes of strong and weak analogies. Figure 4
presents the polarity and subjectivity distribution of strong and weak analogies. As shown
in the plots, both strong and weak analogies contain sentences with neutral polarity and less
subjectivity. Seventeen POS tags are present in the dataset. Distributions of the three most
prevalent POS tags in strong and weak analogies are depicted in Figure 5 to utilize space
efectively. Nevertheless, we used all 17 POS tags in the SVM classifier as features. Out of the
fourteen named entities in the dataset (that are used in the SVM classifier), the distributions
of the top three (ORG, CARDINAL, and PERSON) are plotted in Figure 6. We use the spaCy
English pipeline 6 for NER tagging. Analogies written by students contain several references
to biochemicals. These are misidentified as organizations (ORG) by spaCy, resulting in the
ORG tag being the top named entity in the dataset. Figure 7 shows the distribution of simple
and complex/ compound sentences. Weak analogies tend to have a slightly higher number of
complex/ compound sentences, and strong analogies have slightly more simple sentences. Figure
8 presents the distributions of word counts, character counts, average word lengths, and unique
word counts of strong and weak analogies. Modest discrepancies between distributions suggest
the potential for such features to distinguish between strong and weak analogies. Therefore a
feature vector combining the abovementioned features (engineered features) was then used in
1https://spacy.io/
2https://matplotlib.org/
3https://seaborn.pydata.org/
4https://github.com/commonsense/conceptnet-numberbatch
5https://tfhub.dev/google/elmo/3
6https://spacy.io/models/en#en_core_web_md
an SVM classifier to classify strong and weak analogies.</p>
        <p>We use five variants of sentence vectors as inputs to the SVM classifier and K-means clustering.
The first variant is the ELMo embeddings vector (ELMo). The second variant is the CNNB
embeddings vector (CNNB), and the third variant is the engineered features vector with the
vector dimension of 44. The fourth variant is a simple concatenation between ELMo embeddings
and the engineered feature vector (ELMo composite). The fifth variant is a simple concatenation
between CNNB embeddings and the engineered feature vector (CNNB composite).</p>
        <p>
          We opted to train an SVM classifier with stratified K-fold cross validation due to the limited
size of our dataset (less than 1000 data points). Due to the imbalanced nature of the dataset and
identifying strong and weak analogies were equally important in this initial analysis, we used
macro-F1 as the performance metric [
          <xref ref-type="bibr" rid="ref34">34</xref>
          ]. Performance of the SVM classifier with five variants
of sentence vectors are listed in table 2.3.
        </p>
        <p>We further inspect the contributions of the engineered features from the four feature
categories mentioned in section 2.2 when discriminating between strong and weak analogies. We
observe (see Figure 9) that most of the top 15 discriminating features belong to the syntactic
feature category, but a semantic feature contributes the most to discriminate between strong
and weak analogies.</p>
        <p>We use K-means to cluster the five variants of sentence vectors mentioned above with cluster
centers randomly selected and K set to two. Based on the Rand index 7, the clusters are not well
7https://scikit-learn.org/stable/modules/clustering.html#rand-index
segregated in any variant, yet engineered features embeddings performed slightly better (see
Table 2.3).</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. Discussion</title>
      <p>This section presents our findings and insights, followed by the limitations and future work.</p>
      <sec id="sec-3-1">
        <title>3.1. Findings and Insights</title>
        <p>We introduce the DAF pipeline to identify discriminative features of strong and weak analogies.
We show that just a few engineered features does a surprisingly good job as input to SVM. To
be sure, the ELMo composite sent through the SVM classifier performs better than the rest of
the sentence vector variants. Nevertheless, the ELMo composite score is slightly higher (∼ 0.03)
than the ELMo. This increase highlights that the engineered features encode some aspects of the
analogies not well-captured by the ELMo embeddings. Although the SVM’s performance with
the engineered feature vector is 26% lower than that of the ELMo embedding, its embedding size
is ∼ 23 times smaller than the ELMo. This phenomenon hints that considerable performance
gains can be achieved with a much smaller number of better hand-crafted features, and most
importantly, the better performance is explainable. We also note that the CNNB composite
vector’s performance in SVM is slightly poorer than that of the CNNB itself (∼ 0.02). Although
further exploration is required to explain this phenomenon clearly, we suspect this may be the
result of feature multicollinearity specific to the manner in which CNNB creates its embeddings,
combined with idiosyncracies of the subsets constructed in cross-validation.</p>
        <p>We show that, among the features passed to the SVM classifier, the most discriminative
feature for classification is a semantic feature (unique attribute count) and three out of the
four semantic features (unique relations count, unique concepts count, concepts count) fall
in the list of top 15 discriminative features. Also, among the top 15 discriminative features,
syntactic features have the most representation. Overall, the engineered features are few in
number, meaningful, and relatively cheap to calculate. Given the range of content in the data
set –anything from marbles to cake–the modest success reported here is impressive. These
features will contribute to our future eforts based on more computationally intensive semantic
analysis. A successful unsupervised learning method would liberate classifier training from
dependence on manual annotation. Unsupervised learning results remain largely unimpressive.
Nevertheless, there are some hints of promise. Engineered features improve clustering results
relative to embeddings alone or embeddings and engineered features. This reinforces our claim
that such features are identifying discriminators that are not captured by embeddings.</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Limitations and Future Work.</title>
        <p>
          The dataset used in this work is imbalanced, with more strong analogy data points than weak
ones. This may cause the “uniform efect" where K-means produces clusters of the same size,
even when the “true" cluster sizes of the dataset are varied [
          <xref ref-type="bibr" rid="ref35">35</xref>
          ]. To overcome such issues we
plan to improve class imbalance through SMOTE [
          <xref ref-type="bibr" rid="ref36">36</xref>
          ], GANS[
          <xref ref-type="bibr" rid="ref37">37</xref>
          ], and the expansion of the
manually-annotated corpus.
        </p>
        <p>The natural language processing techniques employed in this work do not handle the
particular nature of the dataset. For example, the spaCy model we use is trained on a generic English
corpus 8. However, we plan to use models/ techniques trained on subject-specific corpora to
overcome issues like misidentifying biochemical terms as organizations in NER. Also, students
use the term “like" in their target analogies to signify the similarity between their analogy
and the source domain (biochemistry) concept. These are wrongly picked up by the sentiment
analysis tool when evaluating polarity. Modified corpora will allow us to better manage these
issues.</p>
        <p>We classified analogy strength using individual sentences, which is both a benefit and a
limitation. As a result, we identified very simple discriminators. However, some sentences in
the dataset might not contribute when creating strong/ weak analogies. Constraining analysis
to the sentence level requires annotation to eliminate this potential source of noise. However,
the long-term goal is to evaluate analogies at the document level, for their epistemic quality.
Though still vector based, our ongoing work in this area employs referent knowledge bases for
both the target and variable student sources, to guide semantic interpretation.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Conclusion</title>
      <p>This work introduces the DAF pipeline to identify discriminative features between strong
and weak long-form analogies. We show that an SVM-based supervised-learning approach
can successfully discriminate component sentences drawn from strong and weak analogies.
Semantic and several syntactic features are the main contributors to discrimination, helping us
to realize our goal of eficient evaluation of student generated long-form analogies.</p>
    </sec>
    <sec id="sec-5">
      <title>Acknowledgments</title>
      <p>We thank Dr. Biplav Srivastava for his valuable feedback and Dr. Nitin Jain for providing the
data used in this work. We also thank the reviewers for their constructive comments.</p>
    </sec>
  </body>
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