Towards Topic-to-Question Generation

Yllias Chali∗
University of Lethbridge

Sadid A. Hasan
Philips Research North America

∗∗

This paper is concerned with automatic generation of all possible questions from a topic of
interest. Konkret, we consider that each topic is associated with a body of texts containing
useful information about the topic. Dann, questions are generated by exploiting the named entity
information and the predicate argument structures of the sentences present in the body of texts.
The importance of the generated questions is measured using Latent Dirichlet Allocation by
identifying the subtopics (which are closely related to the original topic) in the given body of
texts and applying the Extended String Subsequence Kernel to calculate their similarity with
the questions. We also propose the use of syntactic tree kernels for the automatic judgment of
the syntactic correctness of the questions. The questions are ranked by considering both their
importance (in the context of the given body of texts) and syntactic correctness. To the best of
our knowledge, no previous study has accomplished this task in our setting. A series of exper-
iments demonstrate that the proposed topic-to-question generation approach can signiﬁcantly
outperform the state-of-the-art results.

1. Einführung

We live in an information age where all kinds of information is easily accessible through
the Internet. The increasing demand for access to different types of information avail-
able online have interested researchers in a broad range of Information Retrieval–related
Bereiche, such as question answering, topic detection and tracking, summarization, multi-
media retrieval, chemical and biological informatics, text structuring, and text mining.
Although search engines do a remarkable job in searching through a heap of informa-
tion, they have certain limitations, as they cannot satisfy the end users’ information
need to have more direct access to relevant documents. Zum Beispiel, if we ask for the
impact of the current global ﬁnancial crisis in different parts of the world, we can expect
to sift through thousands of results for the answer. This fact can be more understandable
by the following scenario. When a user enters a query, they are served with a ranked list
of relevant documents by the standard document retrieval systems (d.h., search engines),

∗ University of Lethbridge, 4401 University Drive West, Lethbridge, Alberta, T1K 3M4, Kanada.

Email: chali@cs.uleth.ca.

∗∗ Philips Research North America, 345 Scarborough Rd, Briarcliff Manor, New York, 10510, USA.

Email: sadid.hasan@philips.com.

Einreichung erhalten: 19 Mai, 2013; revised submission received: 26 Mai, 2014; zur Veröffentlichung angenommen:
22 Juni, 2014.

doi:10.1162/COLI a 00206

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and their search task is usually not over (Chali, Joty, and Hasan 2009). The next step
for the user is to look into the documents themselves and search for the precise piece of
information they were looking for. This method is time-consuming, and a correct
answer could easily be missed by either an incorrect query resulting in missing
documents or by careless reading. This is why Question Answering (QA) has received
immense attention from the information retrieval, information extraction, machine
learning, and natural language processing communities in the last 15 Jahre (Hirschman
and Gaizauskas 2001; Strzalkowski and Harabagiu 2008; Kotov and Zhai 2010).

The main goal of QA systems is to retrieve relevant answers to natural language
questions from a collection of documents rather than using keyword matching tech-
niques to extract documents. Automated QA research focuses on how to respond with
exact answers to a wide variety of questions, einschließlich: factoid, list, deﬁnition, Wie,
Warum, hypothetical, semantically constrained, and crosslingual questions (Simmons 1965;
Kupiec 1993; Voorhees 1999; Hirschman and Gaizauskas 2001; Greenwood 2005; Wang
2006; Moldovan, Clark, and Bowden 2007). One of the main requirements of a QA
system is that it must receive a well-formed question as input in order to come up
with the best possible correct answer as output. Available studies revealed that humans
are not very skilled in asking good questions about a topic of their interest. Sie sind
forgetful in nature; this often restricts them to properly express whatever that is peeking
in their mind. daher, they would beneﬁt from automated Question Generation (QG)
systems that can assist in meeting their inquiry needs (Lauer, Peacock, and Graesser
1992; Graesser et al. 2001; Rus and Graesser 2009; Ali, Chali, and Hasan 2010; Kotov
and Zhai 2010; Olney, Graesser, and Person 2012). Another beneﬁt of QG is that it can
be a good tool to help improve the quality of the QA systems (Graesser et al. 2001; Rus
and Graesser 2009). These beneﬁts of a QG system motivate us to address the important
problem of topic-to-question generation, where the main goal is to generate all possible
questions about a given topic. Zum Beispiel, given the topic Apple Inc. Logos, we would
like to generate questions such as What is Apple Inc.?, Where is Apple Inc. located?, Who
designed Apple’s Logo?, und so weiter.

The problem of topic-to-question generation can be viewed as a generalization
of the problem of answering complex questions. Complex questions are essentially
broader information requests about a certain topic, whose answers could be obtained
from pieces of information scattered in multiple documents. Zum Beispiel, consider the
complex question:1 Describe steps taken and worldwide reaction prior to the introduction
of the Euro on January 1, 1999. Include predictions and expectations reported in the press.
This question is requesting an elaboration about the topic “Introduction of the Euro,”
which can be answered by following complex procedures such as question decom-
position or inferencing and synthesizing information from multiple documents (z.B.,
multi-document summarization). Answering complex questions is not easy as it is not
always understandable to which direction one should move to search for the answer
to a complex question. This situation arises because of the wider focus of the topic
that is inherent in the complex question in consideration. Zum Beispiel, a complex
question like Describe the tsunami disaster in Japan has a wider focus without a single
or well-deﬁned information need. To narrow down the focus, this question can be
decomposed into a series of simple questions such as How many people were killed in the
tsunami?, How many people became homeless?, Which cities were mostly damaged?, und so weiter.

1 The example complex questions have been provided according to the guidelines of the Document

Understanding Conference (DUC, http://duc.nist.gov/) (2005–2007) tasks.

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Chali and Hasan

Towards Topic-to-Question Generation

Decomposing a complex question automatically into simpler questions in this manner
such that each of them can be answered individually by using the state-of-the-art QA
Systeme, and then combining the individual answers to form a single answer to the
original complex question, has proven effective to deal with the complex question
answering problem (Harabagiu, Lacatusu, and Hickl 2006; Hickl et al. 2006; Chali,
Hasan, and Imam 2012). Darüber hinaus, the generated simple questions can be used as the
list of important aspects to act as a guide2 for selecting the most relevant sentences in
producing more focused and more accurate summaries as the output of a summariza-
tion system (Chali, Hasan, and Imam 2011, 2012). From this discussion, it is obvious
that the complex question decomposition problem can be generalized to the problem of
topic-to-question generation to help improve the complex question answering systems.
In this article3, we consider the task of automatically generating questions from
topics and assume that each topic is associated with a body of texts having useful
information about the topic. This assumption has been inherited from the process of
how a human asks questions based on their knowledge. Zum Beispiel, if a person knows
that a university is an educational institution, then they can ask a question about its
faculty and students. In this research, our main goal is to generate fact-based questions4
about a given topic from its associated content information. We generate questions by
exploiting the named entity information and the predicate argument structures of the
Sätze (along with semantic roles) present in the given body of texts. The named
entities and the semantic role labels are used to identify relevant parts of a sentence in
order to form relevant questions about them. The importance of the generated questions
is measured in two steps. In the ﬁrst step, we identify whether the question is asking
something about the topic or something that is very closely related to the topic. We call
this the measure of topic relevance. For this purpose, we use Latent Dirichlet Allocation
(LDA) (Blei, Ng, und Jordanien 2003) to identify the subtopics (which are closely related to
the original topic) in the given body of texts and apply the Extended String Subsequence
Kernel (ESSK) (Hirao et al. 2003) to calculate their similarity with the questions. Im
second step, we judge the syntactic correctness of each generated question. Wir bewerben uns
the tree kernel functions (Collins and Duffy 2001) and re-implement the syntactic tree
kernel model according to Moschitti et al. (2007) for computing the syntactic similarity
of each question with the associated content information. We rank the questions by
considering their topic relevance and syntactic correctness scores. Experimental results
show the effectiveness of our approach for automatically generating topical questions.
The remainder of the article is organized as follows. Abschnitt 2 describes the related work.
Abschnitt 3 presents the description of our QG system. Abschnitt 4 explains the experiments
and shows evaluation results; Abschnitt 5 concludes.

2. Related Work

Kürzlich, question generation has received immense attention from researchers and
different methods have been proposed to accomplish the task in different relevant ﬁelds
(Andrenucci and Sneiders 2005). McGough et al. (2001) proposed an approach to build
a Web-based testing system with the facility of dynamic QG. Wang et al. (2008) showed

2 http://www.nist.gov/tac/2011/Summarization/Guided-Summ.2011.guidelines.html.
3 This article is a longer version of our previously published work (Chali and Hasan 2012c). We provide
more theoretical descriptions and analyses, and conduct our experiments on a larger data set to report
new results.

4 We mainly focus on generating who, what, Wo, welche, Wann, Warum, and how questions in this research.

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a method to automatically generate questions based on question templates (welche sind
created from training on medical articles). Braun, Frishkoff, and Eskenazi (2005) von-
scribed an approach to automatically generate questions to assess the user’s vocabulary
Wissen. Chen, Aist, and Mostow (2009) developed a method to generate questions
automatically from informational text to mimic the reader’s self-questioning strategy
during reading. Andererseits, Agarwal, Shah, and Mannem (2011) berücksichtigt
the question generation problem beyond the sentence level and designed an approach
that uses discourse connectives to generate questions from a given text. Several other
QG models have been proposed over the years that deal with transforming answers
to questions and utilizing question generation as an intermediate step in the question
answering process (Echihabi and Marcu 2003; Hickl et al. 2005). There are some other
researchers who have approached the task of generating questions for educational
Zwecke (Mitkov and Ha 2003; Heilman and Smith 2010b).

Question asking and QG are important components in advanced learning technolo-
gies such as intelligent tutoring systems and inquiry-based environments (Graesser
et al. 2001). A QG system is useful for building better question-asking facilities in in-
telligent tutoring systems. The Natural Language Processing (NLP), Natural Language
Generation, Intelligent Tutoring System, and Information Retrieval communities have
currently identiﬁed the Text-to-Question generation task as promising candidates for
shared tasks5 (Rus and Graesser 2009; Boyer and Piwek 2010). In the Text-to-Question
generation task, a QG system is given a text, and the goal is to generate a set of questions
for which the text contains answers. The task of generating a question about a given text
can be typically decomposed into three subtasks. Erste, given the source text, a content
selection step is necessary to select a target to ask about, such as the desired answer.
Zweite, given a target answer, an appropriate question type is selected (d.h., the form of
question to ask is determined). Dritte, given the content and question type, the actual
question is constructed. Based on this principle, several approaches have been described
in Boyer and Piwek (2010) that use named entity information, syntactic knowledge, Und
semantic structures of the sentences to perform the task of generating questions from
sentences and paragraphs (Heilman and Smith 2010a; Mannem, Prasad, and Joshi 2010).
Inspired by these works, we perform the task of topic-to-question generation using
named entity information and semantic structures of the sentences. A task that is similar
to ours is the task of keywords-to-question generation that has been addressed recently
in Zheng et al. (2011). They propose a user model for jointly generating keywords and
Fragen. Jedoch, their approach is based on generating question templates from
existing questions, which requires a large set of English questions as training data. In
recent years, some other related researchers have proposed the tasks of high-quality
question generation (Ignatova, Bernhard, and Gurevych 2008) and generating ques-
tions from queries (Lin 2008). Fact-based question generation has been accomplished
previously (Rus, Cai, and Graesser 2007; Heilman and Smith 2010b). We also focus on
generating fact-based questions in this research.

Besides grammaticality, an effective QG system should focus deeply on the im-
portance of the generated questions (Vanderwende 2008). This motivates the use of
a question-ranking module in a typical QG system. Over-generated questions can be
ranked using different approaches, such as statistical ranking methods, dependency
parsing, identiﬁcation of the presence of pronouns and named entities, and topic scoring
(Heilman and Smith 2010a; Mannem, Prasad, and Joshi 2010; McConnell et al. 2011).

5 http://www.questiongeneration.org/QGSTEC2010.

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Jedoch, most of these automatic ranking approaches ignore the aspects of complex
paraphrasing by not considering lexical semantic variations (z.B., synonymy) Wann
measuring the importance of the questions. In our work, we use LDA (Blei, Ng, Und
Jordanien 2003) to identify the subtopics (which are closely related to the original topic) In
the given body of texts. We choose LDA because in recent years it has become one of the
most popular topic modeling techniques and has been shown to be effective in several
text-related tasks, such as document classiﬁcation, information retrieval, and question
answering (Wei and Croft 2006; Misra, Capp´e, and Yvon 2008; Celikyilmaz, Hakkani-
Tur, and Tur 2010).

Once we have the subtopics, we apply ESSK (Hirao et al. 2003) to calculate their sim-
ilarity with the generated questions. The choice of ESSK is motivated by its successful
use in different NLP tasks in recent years (Chali, Hasan, and Joty 2009, 2011; Chali and
Hasan 2012a, 2012B). Hirao et al. (2003) introduced ESSK considering all possible senses
of each word to perform their summarization task. Their method is effective. Jedoch,
the fact that they do not disambiguate word senses cannot be disregarded. In our task,
we apply ESSK to calculate the similarity between important topics (discovered using
LDA) and the generated questions in order to measure the importance of each question.
We use disambiguated word senses for this purpose.

Syntactic information has previously been used successfully in question answering
(Zhang and Lee 2003; Moschitti and Basili 2006; Moschitti et al. 2007; Chali, Hasan, Und
Joty 2009, 2011). Pasca and Harabagiu (2001) argued that with the syntactic form of
a sentence one can see which words depend on other words. We also feel that there
should be a similarity between the words that are dependent in the sentences present
in the associated body of texts and the dependency between words of the generated
question. This motivates us to propose the use of syntactic kernels in judging the
syntactic correctness of the generated questions automatically.

The main goal of our work is to generate as many questions as possible related to the
topic. We use the named entity information and the predicate argument structures of the
sentences to accomplish this goal. Our approach is different from the set-up in shared
tasks (Rus and Graesser 2009; Boyer and Piwek 2010), as we generate a set of basic
questions that are useful to add variety in the question space. A paragraph associated
with each topic is used as the source of relevant information about the topic. We evaluate
our systems in terms of topic relevance, which is different from prior research (Heilman
and Smith 2010a; Mannem, Prasad, and Joshi 2010). Syntactic correctness is also an
important property of a good question. Aus diesem Grund, we evaluate our system in
terms of syntactic correctness as well. The proposed system will be useful for generating
topic-related questions from the associated content information, which can be used to
incorporate a “question suggestions for a certain topic” facility in search systems (Kotov
and Zhai 2010). Zum Beispiel, if a user searches for some information related to a certain
topic, the search system could generate all possible topic-relevant questions from a pre-
existent related body of texts to provide suggestions. Kotov and Zhai (2010) approached
a similar task by proposing a technique to augment the standard ranked list presenta-
tion of search results with a question-based interface to reﬁne user-given queries.

The major contributions of our work can be summarized as follows:
(cid:2)

We perform the task of topic-to-question generation, which can help users
in expressing their information needs. Questions are generated using a
set of general-purpose rules based on named entity information and the
predicate argument structures of the sentences (along with semantic roles)
present in the associated body of texts.

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(cid:2)

We identify the subtopics (which are closely related to the original topic) In
the given body of texts by using LDA and calculate their similarity with
the questions by applying ESSK (with disambiguated word senses). Das
helps us to measure the importance of each question.

We compute the syntactic similarity of each question with its associated
content information by applying the tree kernel functions with the
re-implementation of the syntactic tree kernel model. In this way, we judge
the syntactic correctness of each generated question automatically.

We evaluate the ESSK similarity scores and the syntactic similarity scores
in a ranking framework and show that the use of ESSK and syntactic
kernels improve the relevance and the syntactic correctness of the
top-ranked questions, jeweils.

We identify circumstances in which our approach performs well and show
Das, using additional experiments by narrowing down the topic focus.
Experiments with the topics about people (biographical focus) aufdecken
improvements in the overall results.

3. Topic-to-Question Generation

Our QG approach mainly builds on four steps. In the ﬁrst step, complex sentences
(from the given body of texts) related to a topic are simpliﬁed, as it is easier to
generate questions from simple sentences. In the next step, named entity information
and predicate argument structures of the sentences are extracted and are then used
to generate questions. In the third step, LDA is used to identify important subtopics
from the given body of texts, and then ESSK is applied to ﬁnd their similarity with
the generated questions. In the ﬁnal step, a syntactic tree kernel is used and syntactic
similarity between the generated questions and the sentences present in the body of
texts determines the syntactic correctness of the questions. Questions are then ranked
by considering the ESSK similarity scores and the syntactic similarity scores. We present
an architectural diagram (Figur 1) to show the different components of our system
and describe the overall procedure in the following subsections.

3.1 Sentence Simpliﬁcation

Sentences may have complex grammatical structure with multiple embedded clauses.
daher, the ﬁrst step of our proposed system is to simplify the complex sentences
with the intention of generating more accurate questions. We use the simpliﬁed fac-
tual statement extractor model6 of Heilman and Smith (2010A). Their model extracts
the simpler forms of the complex source sentence by altering lexical items, syntactic
Struktur, and semantics, as well as by removing phrase types such as leading conjunc-
tionen, sentence-level modifying phrases, and appositives. Zum Beispiel, given a complex
sentence s, we get the corresponding simple sentences as follows:

Complex Sentence (S): Apple’s ﬁrst logo, designed by Jobs and Wayne, depicts Sir Isaac

Newton sitting under an apple tree.

Simple Sentence (1): Apple’s ﬁrst logo is designed by Jobs and Wayne.

6 Available at http://www.ark.cs.cmu.edu/mheilman/questions/.

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Figur 1
Architectural diagram of our system.

Simple Sentence (2): Apple’s ﬁrst logo depicts Sir Isaac Newton sitting under an

apple tree.

3.2 Named Entity Information and Semantic Role Labeling for QG

In the second step of our system, we at ﬁrst process the simple sentences in order to
generate all possible questions from them. We use the Illinois Named Entity Tagger,7 A
state-of-the-art named entity (NE) tagger that tags plain text with named entities (peo-
Bitte, Organisationen, Standorte, miscellaneous) (Ratinov and Roth 2009). Once we tag the
topic under consideration and its associated body of texts, we use some general purpose
rules to create some basic questions even though the answer is not present in the body
of texts. Zum Beispiel, Apple Inc. is tagged as an organization, so we generate a question:
Where is Apple Inc. located?. The main motivation behind generating such questions is
to add variety to the generated question space. The basic questions are useful when
there is very little or no knowledge available for a certain topic in consideration. Das
assumption is inherited from the scenario in the real world where a human can ask
questions having very limited background knowledge about the topic. Zum Beispiel,
if a person knows nothing about a university, they can ask What is it? oder, if they at
least know that a university is an institution, then they can ask the question, Where is
it located?. In Table 1, we show some example rules for the basic questions generated
in this work.

Our next task is to generate speciﬁc questions from the sentences present in the
given body of texts. For this purpose, we parse the sentences semantically using a

7 Available at http://cogcomp.cs.illinois.edu/.

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Tisch 1
Example basic question rules.

Tag

Example Question

person
Who is person?
organization Where is organization located?
location
misc.

Where is location?
What do you know about misc.?

Semantic Role Labeling (SRL) System (Kingsbury and Palmer 2002; Hacioglu et al. 2003),
ASSERT.8 ASSERT is an automatic statistical semantic role tagger that can annotate
naturally occuring text with semantic arguments. When presented with a sentence, Es
performs a full syntactic analysis of the sentence, automatically identiﬁes all the verb
predicates in that sentence, extracts features for all constituents in the parse tree relative
to the predicate, and identiﬁes and tags the constituents with the appropriate semantic
arguments. Zum Beispiel, the output of the SRL system for the sentence Apple’s ﬁrst
logo is designed by Jobs and Wayne is: [ARG1 Apple ’s ﬁrst logo] Ist [TARGET designed ]
[ARG0 by Jobs and Wayne]. The output contains one verb (predicate) with its arguments
(d.h., semantic roles). These arguments are used to generate speciﬁc questions from the
Sätze. Zum Beispiel, we can replace [ARG1 ..] with What and generate a question as:
What is designed by Jobs and Wayne?. Ähnlich, [ARG0 ..] can be replaced and the question:
Who designed Apple’s ﬁrst logo? can be generated. The semantic roles ARG0…ARG5 are
called mandatory arguments. There are some additional arguments or semantic roles
that can be tagged by ASSERT. They are called optional arguments and they start with
the preﬁx ARGM. These are deﬁned by the annotation guidelines set in Palmer, Gildea,
and Kingsbury (2005). A set of about 350 general-purpose rules are used to transform
the semantic-role labeled sentences into the questions. The rules were set up in a way
that we could use the semantic role information to ﬁnd the potential answer words in a
sentence that would be replaced by suitable question words. In the case of a mandatory
Streit, the choice of question word depends on the argument’s named entity tag
(who for a person, where for a location, usw.). Tisch 2 shows how different semantic roles
can be replaced by possible question words in order to generate a question.

3.3 Importance of Generated Questions

In the third step of our proposed system, we pass the generated questions to the
importance judgment module that uses LDA and ESSK to assign a topic relevance score
to each question. The detailed procedure is discussed in the following subsections.

3.3.1 Latent Dirichlet Allocation (LDA). To measure the importance of the generated
Fragen, we use LDA (Blei, Ng, und Jordanien 2003) to identify the important subtopics9
from the given body of texts. LDA is a probabilistic topic modeling technique where
the main principle is to view each document as a mixture of various topics. Here each
topic is a probability distribution over words. LDA assumes that documents are made

8 Available at http://cemantix.org/assert.html.
9 The term sub-topic is used in the LDA topic modeling sense, which represents a probability distribution

over words.

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Tisch 2
Semantic roles with possible question words.

Arguments

Question Words

ARG0…ARG5 who, Wo, what, welche
ARGM-ADV
ARGM-CAU
ARGM-DIS
AGRM-EXT
ARGM-LOC
ARGM-MNR
ARGM-PNC
ARGM-TMP

in what circumstances
Warum
Wie
to what extent
Wo
Wie
Warum
Wann

up of words and word ordering is not important (“bag-of-words” assumption) (Misra,
Capp´e, and Yvon 2008). The main idea is to choose a distribution over topics while
generating a new document. For each word in the new document, a topic is randomly
chosen according to this distribution and a word is drawn from that topic. LDA uses
a generative topic modeling approach to specify the following distribution over words
within a document:

P(wi) =

K(cid:2)

j=1

P(wi

|zi

= j)P(zi

= j)

(1)

|zi

= j) is the probability of word wi under topic j,
where K is the number of topics, P(wi
= j) is the sampling probability of topic j for the ith word. The multinomial
and P(zi
distributions φ(J) = P(w|zi
= j) and θ(D) = P(z) are termed as topic-word distribution
and document-topic distribution, jeweils (Blei, Ng, und Jordanien 2003). A Dirichlet
(α) prior is placed on θ and a Dirichlet (β) prior is set on φ to reﬁne this basic model
(Grifﬁths and Steyvers 2002; Blei, Ng, und Jordanien 2003). Now the main goal is to
estimate the two parameters: θ and φ. We apply this framework directly to solve our
problem by considering each topic-related body of texts as a document. We use a GUI-
based toolkit for topic modeling10 that uses the popular MALLET (McCallum 2002)
toolkit for the back-end. The LDA model is built on the development set11 (Abschnitt 4.2).
The process starts by removing a list of “stop words” from the document and runs 200
iterations of Gibbs sampling (Geman and Geman 1984) to estimate the parameters θ
and φ. From each body of texts, we discover K topics and choose the most frequent
words from the most likely unigrams as the desired subtopics. Zum Beispiel, von dem
associated body of texts of the topic Apple Inc. Logos, we get these subtopics: janoff,
themes, logo, color, apple.

3.3.2 Extended String Subsequence Kernel (ESSK). Once we identify the subtopics, Wir
apply ESSK (Hirao et al. 2003) to measure their similarity with the generated questions.
In the general ESSK, each word in a sentence is considered an “alphabet,” and the
alternative is all its possible senses. Jedoch, our ESSK implementation considers the

10 Available at http://code.google.com/p/topic-modeling-tool/.
11 The model was built and tested according to the guidelines of the topic modeling toolkit we used.

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Computerlinguistik

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alternative of each word as its disambiguated sense. We use a dictionary-based Word
Sense Disambiguation (WSD) System (Chali and Joty 2007) assuming one sense per
Diskurs. We use WordNet (Fellbaum 1998) to ﬁnd the semantic relations (wie zum Beispiel
repetition, synonym, hypernym and hyponym, holonym and meronym, and gloss)
for all the words in a text. We assign a weight to each semantic relation based on
heuristics and use all of them. Our WSD technique is decomposed into two steps: (1)
building a representation of all possible senses of the words and (2) disambiguating
the words based on the highest score. To be speciﬁc, each candidate word from the
context is expanded to all of its senses. A disambiguation graph is constructed as the
intermediate representation where the nodes denote word instances with their WordNet
senses, and the weighted edges (connecting the senses of two different words) vertreten
semantic relations. This graph is exploited to perform the WSD. We sum the weights of
all edges, leaving the nodes under their different senses. The sense with the highest
score is considered to be the most probable sense. In case of a tie between two or
more senses, we select the sense that comes ﬁrst in WordNet, because WordNet orders
the senses of a word by decreasing order of their frequency. Our preliminary experi-
ments suggested that WSD has a positive impact on the performance of our proposed
System.

ESSK is used to measure the similarity between all possible subsequences of
the question words/senses and topic words/senses. We calculate the similarity score
Sim(Ti, Qj) using ESSK, where Ti denotes a topic/sub-topic word sequence and Qj
stands for a generated question. Formally, ESSK is deﬁned as follows:12

Kessk(T, Q) =

D(cid:2)

(cid:2)

m=1

∈T

∈Q

Km(ti, qj)

(cid:3)

Km(ti, qj) =

(cid:2)

val(ti, qj)
m−1(ti, qj) · val(ti, qj)
K

if m = 1

(cid:2)

Hier, K
M(ti, qj) is deﬁned in the following. ti and qj are nodes of T and Q, jeweils.
The function val(T, Q) returns the number of common attributes (d.h., the number of
common words/senses) to the given nodes t and q.

(cid:3)

(cid:2)

M(ti, qj) =
K

0
λK

(cid:2)

M(ti, qj−1) + K

M(ti, qj−1)

(cid:2)(cid:2)

if j = 1

Hier, λ is the decay parameter for the number of skipped words. K
deﬁned as:

(cid:2)(cid:2)

M(ti, qj) Ist

(cid:3)

(cid:2)(cid:2)

M(ti, qj) =
K

0
λK

(cid:2)(cid:2)

M(ti−1, qj) + Km(ti−1, qj)

if i = 1

12 The formulae denote a dynamic programming technique to compute the ESSK similarity score
where d is the vector space dimension (d.h., the number of all possible subsequences of up to
length d). More information about these formulae can be obtained from Hirao et al. (2003, 2004).

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Endlich, the similarity measure is deﬁned after normalization:

simessk(T, Q) =

(cid:4)

Kessk(T, Q)
Kessk(T, T)Kessk(Q, Q)

3.4 Judging Syntactic Correctness

The next step of our system is to judge the syntactic correctness of the generated
Fragen. The generated questions might be syntactically incorrect due to the pro-
cess of automatic question generation. It is time-consuming and considerable human
intervention is necessary to check for the syntactically incorrect questions manually. Wir
strongly believe that a question should have a similar syntactic structure to a sentence
from which it is generated. Zum Beispiel, the sentence Apple’s ﬁrst logo is designed by
Jobs and Wayne., and the generated question What is designed by Jobs and Wayne? Sind
syntactically similar. An example of an ungrammatical generated question that is not
very similar to its source is: Janoff presented Jobs What?. To judge the syntactic cor-
rectness of each generated question automatically, we apply the tree kernel functions
and re-implement the syntactic tree kernel model according to Moschitti et al. (2007)
for computing the syntactic similarity of each question with the associated content
Information. We ﬁrst parse the sentences and the questions into syntactic trees using the
Charniak parser13 (Charniak 1999). Dann, we calculate the similarity between the two
corresponding trees using the tree kernel method (Collins and Duffy 2001). We convert
each parenthetic representation generated by the Charniak parser into its corresponding
tree and give the trees as input to the tree kernel functions for measuring the syntactic
Ähnlichkeit.

The tree kernel function computes the number of common subtrees between two
trees and gives the similarity score between each sentence in the given body of texts and
the generated question based on the syntactic structure. Each sentence14 contributes a
score to the questions and then the questions are ranked by considering the average of
similarity scores.

4. Experimente

4.1 System Description

We consider the task of automatically generating questions from topics where each
topic is associated with a body of texts having a useful description about the topic.
The question-ranking module of the proposed QG system ranks the questions by com-
bining the topic relevance scores and the syntactic similarity scores of Section 3.3 Und
Abschnitt 3.4 using the following formula:

w ∗ ESSKscore

+ (1 − w) ∗ SYNscore

(2)

13 Verfügbar unter https://github.com/BLLIP/bllip-parser.
14 We consider that a question is syntactically ﬂuent as well as relevant to the topic if it has similar syntactic

subtrees to those of the most sentences in the body of texts.

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Computerlinguistik

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Hier, w is the importance parameter, which holds a value in [0, 1]. We kept w = 0.5 Zu
give equal importance15 to topic relevance and syntactic correctness.

4.2 Corpus

To run our experiments, we use the data set provided in the Question Generation
Shared Task and Evaluation Challenge16 (2010) for the task of question generation
from paragraphs. This data set consists of 60 paragraphs about 60 topics that were
originally collected from several Wikipedia, OpenLearn, and Yahoo!Answers articles.
The paragraphs contain around 5–7 sentences for a total of 100–200 tokens (einschließlich
punctuation). This data set includes a diversity of topics of general interest. We consider
these topics and treat the paragraphs as their associated useful content information
in order to generate a set of questions using our proposed QG approach. We ran-
domly select 10 topics and their associated paragraphs as the development data.17
A total of 2,186 questions are generated from the remaining 50 topics (test data) Zu
be ranked.

4.3 Evaluation Set-up
4.3.1 Methodik. We use a methodology derived from Boyer and Piwek (2010)
and Heilman and Smith (2010B) to evaluate the performance of our QG systems.
Three native English-speaking university graduate students judge the quality of the
top-ranked 20% questions using two criteria: topic relevance and syntactic correctness.
For topic relevance, the given score is an integer between 1 (very poor) Und 5 (sehr
good) and is guided by the consideration of the following aspects: 1. Semantic
correctness (d.h., the question is meaningful and related to the topic), 2. Correctness of
question type (d.h., a correct question word is used), Und 3. Referential clarity (d.h., es ist
clearly possible to understand what the question refers to). For syntactic correctness,
the assigned score is also an integer between 1 (very poor) Und 5 (very good). Whether a
question is grammatically correct or not is checked here. The judges were asked to read
the topics with their associated body of texts and then rate the top-ranked questions
generated by different systems. For each question, we calculate the average of the
judges’ scores. The judges were provided with an annotation guideline and sample
judgments, according to the methodology derived from Boyer and Piwek (2010) Und
Heilman and Smith (2010B). The same judges evaluated all the system outputs and
they were blind to the system identity when judging. No guidelines were provided on
the relative importance of the various aspects that made the judgment task subjective.
The inter-annotator agreement of Fleiss’s κ = 0.41, 0.45, 0.62, Und 0.33 are computed
for the three judges for the results in Tables 3–6, indicating moderate (for the ﬁrst
two tables), and substantial and fair agreement (Landis and Koch 1977) between the
raters, jeweils. These κ values were shown to be acceptable in the literature for
the relevant NLP tasks (Dolan and Brockett 2005; Glickman, Dagan, and Koppel 2005;
Heilman and Smith 2010b).

15 A syntactically incorrect question is not useful even if it is relevant to the topic. This motivated us to
give equal importance to topic relevance and syntactic correctness. The parameter w can be tuned to
investigate its impact on the system performance.
16 http://www.questiongeneration.org/mediawiki.
17 We use these data to build necessary general purpose rules for our QG model.

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Tisch 3
Topic relevance and syntactic correctness scores.

Systeme

Topic Relevance

Syntactic Correctness

Baseline1 (No Ranking)
Baseline2 (Topic Signature)
State-of-the-art (Heilman and Smith 2010b)
Proposed QG System

2.15
3.24
3.35
3.48

2.63
3.30
3.45
3.55

4.3.2 Systems for Comparison. We report the performance of the following systems in
order to do a meaningful comparison with our proposed QG system:

(1) Baseline1: This is our QG system without any question-ranking method applied to
Es. Hier, we randomly select top 20% questions and rate them.
(2) Baseline2: For our second baseline, we build a QG system using an alternative topic
modeling approach. Hier, we use a topic signature model (instead of using LDA as
discussed in Section 3.3.1) (Lin and Hovy 2000) to identify the important subtopics from
the sentences present in the body of texts. The subtopics are the important words in the
context that are closely related to the topic and have signiﬁcantly greater probability of
occurring in the given text compared with a large background corpus. We use a topic
signature computation tool18 for this purpose. The background corpus that is used in
this tool contains 5,000 documents from the English GigaWord Corpus. Zum Beispiel,
from the given body of texts of the topic Apple Inc. Logos, we get these subtopics: jobs,
logo, themes, rainbow, monochromatic. Then we use the same steps of Sections 3.3.2 Und
3.4, and use Equation (2) to combine the scores. We evaluate the top-ranked 20%
questions and show the results.
(3) State-of-the-art: We choose a publicly available state-of-the-art QG system19 to
generate questions from the sentences in the body of texts. This system was shown
to achieve good performance in generating fact-based questions about the content of a
given article (Heilman and Smith 2010b). Their method ranks the questions automat-
ically using a logistic regression model. Given a paragraph as input, this system pro-
cesses each sentence and generates a set of ranked questions for the entire paragraph.
We evaluate the top-ranked 20% questions20 and report the results.

4.3.3 Results and Discussion. Tisch 3 shows the average topic relevance and syntactic
correctness scores for all the systems. From these results, we can see that the proposed QG
system improves the topic relevance and syntactic correctness scores over the Baseline1
system by 62% Und 35%, jeweils, and improves the topic relevance and syntactic
correctness scores over the Baseline2 system by 7%, Und 8%, jeweils. Auf dem anderen
Hand, the proposed QG system improves the topic relevance and syntactic correctness
scores over the state-of-the-art system by 4% Und 3%, jeweils. From these results, Wir
can clearly observe the effectiveness of our proposed QG system. The improvements in
the results are statistically signiﬁcant21 (P < 0.05). The main goal of this work was to generate as many questions as possible related to the topic. For this reason, we considered generating the basic questions. These questions 18 Available at http://www.cis.upenn.edu/∼lannie/topicS.html. 19 Available at http://www.ark.cs.cmu.edu/mheilman/questions/. 20 We ignore the yes-no questions for our task. 21 We tested statistical signiﬁcance using Student’s t test. 13 l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o l i / l a r t i c e - p d f / / / / 4 1 1 1 1 8 0 5 0 4 7 / c o l i _ a _ 0 0 2 0 6 p d . f b y g u e s t t o n 0 9 S e p e m b e r 2 0 2 3 Computational Linguistics Volume 41, Number 1 Table 4 Acceptability of the questions (in %). Systems Top 15% Top 30% Baseline1 (No Ranking) Baseline2 (Topic Signature) State-of-the-art (Heilman and Smith 2010b) Proposed QG System 35.2 45.9 44.7 46.5 32.6 33.8 38.5 40.6 Table 5 Topic relevance and syntactic correctness scores (narrowed focus). Systems Topic Relevance Syntactic Correctness Baseline1 (No Ranking) Baseline2 (Topic Signature) State-of-the-art (Heilman and Smith 2010b) Proposed QG System 2.84 3.50 3.63 3.78 2.75 3.42 3.56 3.72 were also useful to provide variety in the question space. We generated these ques- tions using the named entity information. As the performance of the NE taggers were unsatisfactory, we had a few of these questions generated. In most cases, these questions were outranked by other important questions, which included a combination of topics and subtopics to show higher topic relevance score measured by ESSK. Therefore, they do not have a considerable impact on the evaluation statistics. We claim that the overall performance of our systems could be further improved if the accuracy of the NE tagger and the semantic role labeler could be increased. Acceptability Test. In another evaluation setting, the three annotators judge the questions for their overall acceptability as a good question. If a question shows no deﬁciency in terms of the criteria considered for topic relevance and syntactic correctness, it is termed as acceptable. We evaluate the top 15% and top 30% questions separately for each QG system and report the results indicating the percentage of questions rated as acceptable in Table 4. The results indicate that the percentage of the questions rated acceptable is reduced when we evaluate a greater number of questions—which proves the effectiveness of our QG system. Narrowing Down the Focus. We run further experiments by narrowing down the topic fo- cus. We consider only the topics about people (biographical focus). We choose 50 people as our topics from the list of the 20th century’s 100 most inﬂuential people, published in Time magazine in 1999 and obtained the paragraphs containing their biographical information from Wikipedia articles.22 We generate a total of 1, 845 questions from the 50 topics considered and rank them using different ranking schemes as discussed before. We evaluate the top 20% questions using the similar evaluation methodologies and report the results in Table 5. From these results, we can see that the proposed QG 22 http://en.wikipedia.org/wiki/Time 100. 14 l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o l i / l a r t i c e - p d f / / / / 4 1 1 1 1 8 0 5 0 4 7 / c o l i _ a _ 0 0 2 0 6 p d . f b y g u e s t t o n 0 9 S e p e m b e r 2 0 2 3 Chali and Hasan Towards Topic-to-Question Generation Table 6 Acceptability of the questions in % (narrowed focus). Systems Top 15% Top 30% Baseline1 (No Ranking) Baseline2 (Topic Signature) State-of-the-art (Heilman and Smith 2010b) Proposed QG System 38.6 47.1 52.4 55.8 31.5 35.5 40.2 42.0 system improves the topic relevance and syntactic correctness scores over the Baseline1 system by 33% and 35%, respectively, and improves the topic relevance and syntactic correctness scores over the Baseline2 system by 8% and 9%, respectively. Moreover, the proposed QG system improves both the topic relevance and syntactic correctness scores over the state-of-the-art system by 4%. From these results, we can clearly observe the effectiveness of our proposed QG system when we narrow down the topic focus. We also evaluate the top 15% and top 30% questions separately for each QG system and report the results, indicating the percentage of questions rated as acceptable in Table 6. From these tables, we can clearly see the improvements in all the scores for all the QG approaches. This is reasonable because the accuracy of the NE tagger and the semantic role labeler is increased for the biographical data.23 These results further demonstrate that the proposed system is signiﬁcantly better (at p < 0.05) than the other considered systems. We plan to make our created resources available to other researchers. 4.3.4 An Input-Output Example. An input to our systems is, for instance,24 the topic Apple Inc. Logos with the associated content information (body of texts): Apple’s ﬁrst logo, designed by Jobs and Wayne, depicts Sir Isaac Newton sitting under an apple tree. Almost immediately, though, this was replaced by Rob Janoff’s “rainbow Apple”, the now-familiar rainbow-colored silhouette of an apple with a bite taken out of it. Janoff presented Jobs with several different monochromatic themes for the “bitten” logo, and Jobs immediately took a liking to it. While Jobs liked the logo, he insisted it be in color to humanize the company. The Apple logo was designed with a bite so that it would be recognized as an apple rather than a cherry. The colored stripes were conceived to make the logo more accessible, and to represent the fact the monitor could reproduce images in color. In 1998, with the roll-out of the new iMac, Apple discontinued the rainbow theme and began to use monochromatic themes, nearly identical in shape to its previous rainbow incarnation. The output of our systems is the ranked lists of questions. We show an example output in Table 7. To provide a more detailed analysis of our results, the average output scores of the example questions are presented in Table 8. From this table, we can understand how different aspects of the evaluation criteria affected the performance of the different systems. For example, Q1 of the proposed system was given a very good score due to 23 Although a few basic questions were generated compared with other important questions containing topical words, we believe they did not have a considerable impact on the overall performance of our system. 24 The example input text is provided from the Question Generation Shared Task and Evaluation Challenge (QGSTEC 2010) data set that we used for our experiments (Section 4.2). 15 l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o l i / l a r t i c e - p d f / / / / 4 1 1 1 1 8 0 5 0 4 7 / c o l i _ a _ 0 0 2 0 6 p d . f b y g u e s t t o n 0 9 S e p e m b e r 2 0 2 3 Computational Linguistics Volume 41, Number 1 Table 7 System output. Systems Baseline2 State-of-the-art Top-ranked questions Q1: Who presented Jobs with several different monochromatic themes for the bitten logo? Q2: What were conceived to make the logo more accessible? Q3: Who liked the logo? Q1: Whose ﬁrst logo depicts Sir Isaac Newton sitting under an apple tree? Q2: What depicts Sir Isaac Newton sitting under an apple tree? Q3: What did Janoff present Jobs with? Proposed QG System Q1: Who designed Apple’s ﬁrst logo? Q2: What was replaced by Rob Janoff’s “rainbow Apple”? Q3: What were conceived to make the logo more accessible? Table 8 Judgment scores associated with example questions. Systems Question Average score Baseline2 State-of-the-art Q1 Q2 Q3 Q1 Q2 Q3 Proposed QG System Q1 Q2 Q3 3.65 3.42 3.38 3.68 3.63 3.25 4.34 3.50 3.42 its relevance to the topic in consideration. On the other hand, Q3 of the state-of-the-art was assigned a lower score due to its lack of clarity with respect to the topic. 5. Conclusion In this article, we have considered the task of automatically generating questions from topics where each topic is associated with a body of texts containing useful information. The proposed method exploits named entity and semantic role labeling information to accomplish the task. A key aspect of our approach was the use of latent Dirichlet allocation (LDA) to automatically discover the hidden subtopics from the sentences. We have proposed a novel method to rank the generated questions by considering: (1) subtopical similarity determined using ESSK algorithm in combination with word sense disambiguation, and (2) syntactic similarity determined using the syntactic tree kernel based method. We have compared the proposed question generation (QG) system with two baseline systems and one state-of-the-art system. The evaluation results show that the proposed QG system signiﬁcantly outperforms all other considered systems, as our top-ranked system generated questions were found to be better in topic-relevance and syntactic correctness than those of the other systems. Our results demonstrated that judging syntactic correctness of the generated questions using the syntactic tree kernel based model was suitable in our question generation setting. We would like to further 16 l D o w n o a d e d f r o m h t t p : / / d i r e c t . m i t . e d u / c o l i / l a r t i c e - p d f / / / / 4 1 1 1 1 8 0 5 0 4 7 / c o l i _ a _ 0 0 2 0 6 p d . f b y g u e s t t o n 0 9 S e p e m b e r 2 0 2 3 Chali and Hasan Towards Topic-to-Question Generation our research by using other available measures such as an n-gram language model or a parser conﬁdence score (Wagner, Foster, and van Genabith 2009) in order to see how they would perform on the same task. In this article, we have also extended our experiments by narrowing down the topic focus. In this experiment, we have considered people as topics. A rigorous analysis of the evaluation results has revealed that the performance of our proposed QG system can be enhanced if we narrow down the topic focus. 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