A Hierarchical Neural Network for Information Extractionof Product Attribute and Condition Sentences
Yukinori Homma, Kugatsu Sadamitsu, Kyosuke Nishida,
Ryuichiro Higashinaka, Hisako Asano and Yoshihiro Matsuo
NTT Media Intelligence Laboratories, NTT Corporation
1-1 Hikari-no-oka, Yukosuka, 239-0847, Japan{homma.yukinori, sadamitsu.kugatsu, nishida.kyosuke,
higashinaka.ryuichiro, asano.hisako, matsuo.yoshihiro}@lab.ntt.co.jp
Abstract
This paper describes a hierarchical neural network we propose for sentence classification to extract product information from product documents. The network classifies each sentence in adocument into attribute and condition classes on the basis of word sequences and sentence sequences in the document. Experimental results showed the method using the proposed network
significantly outperformed baseline methods by taking semantic representation of word and sentence sequential data into account. We also evaluated the network with two different productdomains (insurance and tourism domains) and found that it was effective for both the domains.

1

Introduction

With the increase in the number of product documents in electronic form, it is becoming increasingly
important to build technologies to extract information from these documents. In particular, it is useful to
extract information about product attributes (such as ”Insurance Premiums”) and their values (such as”$ 0.50 per day”) from web product documents for many applications such as commodity comparison,product recommendation and question answering systems about products. For instance, to provide aquestion answering system that compares particular attributes of products, we need to extract the valuesof common attributes from each product document.
In this study, we tackled the following two problems for extracting information from product documents on the Web. The first and main problem is to classify each sentence into attribute classes and thesecond one is to distinguish whether or not each sentence includes condition information, which is helpful in subdividing the attribute. Figure 1 shows an example insurance product document and an example
of classification results of attribute and condition.

Figure 1: Left: Example of insurance product document. Right: Example of labeled attribute and condition classes.
This work is licensed under a Creative Commons Attribution 4.0 International Licence.
creativecommons.org/licenses/by/4.0/

Licence details: http://

21
Proceedings of the Open Knowledge Base and Question Answering (OKBQA) Workshop,
pages 21–29, Osaka, Japan, December 11 2016.

Attribute sentence classification
Product documents in the Web describe product attributes in different ways, e.g. tables, listings and plain sentences. Although most previous studies have tried to
extract words or phrases presenting product attribute values such as ”size” or ”fee”, from the above
components, we think that it is also useful to extract sentences presenting values such as ”overview”
or ”payment terms” to provide a question answering system that will explain products in the form ofsentences. We therefore tackled the following problem in this study.
Problem 1. Given an HTML/XML document, we classify each sentence into pre-defined attributeclasses, where a sentence consists of a sequence of words and their tag information.
Condition sentence classification
There are some cases in which common attribute classes are notenough for obtaining concrete information that can be used in question answering systems, and this problem is not able to be simply solved by subdividing the pre-defined classes since the concrete information
is product specific. For example, we can see from Figure 1 that there are two special contracts (for family
and for individual) that have different values of the attribute Insured object. We consider that it is helpful
to extract a sentence that presents necessary conditions in each document instead of constructing a detailed taxonomy of product attributes. We therefore focus on extracting sentences describing condition
information.
Problem 2. We also classify each sentence into condition or non-condition classes.
Given information about the classification results of attribute and condition sentences, we can provide
a question answering system which can provide a proper answer based on the terms of conditions. As an
example for Figure 1, when a user asks a question about insured objects of the product, such as ”Whois covered by this insurance?”, and the system understands that the user made a special contract for
an individual, the system can provide an answer such as ”Since you made a special contract for anindividual, the insurance covers only the applicant”.
To classify each sentence accurately, it is important to consider the semantic meanings of a sequenceof sentences and their HTML tag information. For example, sentences in a listing structure will belong
to the same class. A sentence also has a sequence of words, and each word has different importance informing the semantic meanings of the sentence. Recently, recurrent neural networks (RNNs) have beenvery successful in capturing semantic representations of word and sentence sequential data in several
tasks, including machine translation (Bahdanau et al., 2014), Named Entity Recognition (Joshi et al.,2015; Jagannatha and Yu, 2016) and document classification (Yang et al., 2016).
In the work reported in this paper, we attempted to develop a neural network model to capture semantic representations of word and sentence sequential data and classify each sentence in a document into
attributes and condition classes. We developed and here propose a hierarchical neural network that classifies each sentence into attribute and condition classes by learning two classification problems jointly.
Experimental results demonstrated that our network performed better than baseline methods by capturing the semantics and structures of sentences. We also evaluated the network in experiments with two
different product domains (insurance products, tourism products) and found that it is effective for both
the domains.

2

Related work

2.1 Word-level attribute extraction
Many researchers have studied the task of extracting values of attributes in a word or a phrase levelfrom product documents. The work they have done can be classified into two approaches: the patternmatching approach based on structured-tag information (Auer et al., 2007; Muslea et al., 1999; Gulhane
et al., 2011) and the machine learning approach based on the predefined attribute-values dictionary (Nagyand Farkas, 2012; Jagannatha and Yu, 2016).
The pattern matching approach relies on a set of extraction based on structured-tag information. DBpedia (Auer et al., 2007) is one of the huge structured datasets using hand-made patterns. It extracts
structured information from Wikipedia such as infobox templates. Although the hand-made patternbased approach can extract information with high accuracy from documents that have the same document22

structure such as infobox templates, it takes considerable costs to make patterns to extract informationfrom documents that have a different document structure. Some researchers have proposed methods toacquire patterns automatically on the basis of machine learning (Muslea et al., 1999; Gulhane et al.,2011). Muslea et al. (1999) proposed a method to extract the node path of the DOM tree as patterns.
Gulhane et al. (2011) proposed a method to group similar structured pages in a Web site and automatically change patterns to extract information based on the structure of each document. The method toacquire patterns automatically is effective when there are many documents that have similar structures,such as online shopping site documents. However, it is difficult to extract patterns with high accuracy
from web product documents that describe product attributes in different ways.
The machine learning approach has been the one most widely studied during the last decade, and manymethods were proposed to extract values of product attributes (Nagy and Farkas, 2012; Jagannatha andYu, 2016). Nagy and Farkas (2012) proposed a method to extract personal information such as phone
number, occupation, and address from search result pages corresponding to personal name queries. Since
their method focuses on extraction of a value for each attribute from a document and narrows down arange for finding personal information on the basis of the paragraph title, it is difficult to apply thismethod for extraction of several values that are scattered in a document. Jagannatha and Yu (2016)
proposed a method to extract medical events written by a word or a phrase from unstructured text inelectronic health record notes using recurrent neural network frameworks. Their model focuses mainly
on word sequence information, which is effective for extracting word or phrase values about attributes inthe documents. However, since our aim is to extract sentence-level values of attributes in a web productdocument, we use HTML tags as features and focus on capturing the importance of words in a sentence
to classify the sentence by using the attention architecture.
2.2 Sentence-level attribute extraction
A number of related studies have been performed for extracting sentence values of attributes in several
tasks, such as event information extraction (Naughton et al., 2008), extractive summarization (Nishikawa
et al., 2015) and emotion classification (Li et al., 2015). Naughton et al. (2008) evaluated the performanceof a support vector machine classifier and a language modeling approach for the task of identifying thesentences in a document that describe one or more instances of a specified event type. They use the words
of a sentence as features and do not focus on the sentence sequences. Nishikawa et al. (2015) proposeda method for query-oriented extractive summarization to extract information especially from Wikipedia
article for a question answering system. This method can extract sentences that present values of productattributes using semi hidden Markov models that capture the semantic meaning of sentence sequencesin the document. However, since the method depends on a summarization model and extracts sentences
only as a value for each attribute, it cannot extract several values for all attributes and conditions in the
documents. In contrast, our method learns to classify each sentence into attribute and condition classes
by learning two classification problems jointly and extracts information for attributes and conditions
from web documents. These documents are not limited to Wikipedia articles.
Li et al. (2015) proposed a method for sentence-level emotion classification in documents. Theirmethod is based on a factor graph with two layers to model the emotional label dependence in a variable
layer and model the sentence context dependence in a factor layer. Their experimental results showedthat it is effective for sentence-level emotion classification to use both label and context dependence
information. While they did not address the importance of words in a sentence to classify sentences,
this paper addresses that topic in reporting on evaluation results. Moreover, our method uses HTML tag
information as features to extract structural information of documents and classify each sentence into
attribute and condition classes.

3

Proposed network

In our study, we focused on a network that would classify sentences into attribute and condition classes
by learning two classification problems jointly.
Assume that a document has L sentences and the i-th sentence contains Ti words and tag information

23

Figure 2: Architecture of proposed network.
ti . wij with j ∈ [1, Ti ] represents the word in the i-th sentence. ti represents the tag name of a parent
node of the DOM tree corresponding to the i-th sentence.
3.1 Overview of architecture
The overall architecture of the proposed network is shown in Figure 2. The network contains four
components: word encoder, word attention layer, sentence encoder and output layer.
Our network does not learn in an end-to-end manner; we conducted block-wise learning for speedingup the leaning. The learning of the first block of word layers is conducted to obtain a sentence vector,
and that of the second block is conducted to classify each sentence into classes. First, it builds a sentence
vector that represents the classification probability of attribute classes and condition classes by aggregating important words into hidden sentence vectors mi in the word encoder (subsection 3.2) and the word
attention layer (subsection 3.3) to capture semantic meanings of word sequential data. It then classifies
each sentence into pre-defined attribute classes and condition classes (subsection 3.5), taking context
sentences into account (subsection 3.4) and using a sentence vector to capture semantic representationsof sentence sequential data.
In the following subsections, we will present the details of each component.
3.2 Word encoder
The word encoder builds a word embedding vector for every word in the sentence.
Given a sentence with words wij , j ∈ [1, Ti ], all words are first encoded into one-hot vectors. A
one-hot vector xij is a binary vector whose elements are all zeros except for the v-th element, whichcorresponds to the v-th token in a vocabulary V . Then, the one-hot vector xij is encoded into an Edimensional vector eij as the following equation.
eij = W wemb wij
where W wemb ∈ RE∗|V | is a weight matrix and |V | is the size of the vocabulary.

24

(1)

Next, the network focuses on the context of words in the sentence. Recurrent neural networks (RNNs)
with long short-term memory (LSTM) units (Hochreiter and Schmidhuber, 1997) have been successfully
applied to a wide range of natural language processing tasks, such as machine translation (Sutskever etal., 2014), language modeling (Zaremba et al., 2014) and so on. However, since standard LSTM networks process sequences in temporal order, they ignore future context. Bi-directional LSTM (BiLSTM)
networks introduce a layer where the hidden-to-hidden connections flow in opposite temporal order.
These networks are able to exploit information from the past to the future and vice versa.
Our network also has a BiLSTM network architecture. Given an embedded vector sequence{ei1 , ei2 , · · · , eiT }, the network outputs vectors {hi1 , hi2 , · · · , hiT } as the following equations.




fj
 i 
 j 
˜ + W we ej + bwh
 = W wh hj−1 oj 
gj
cj = σ(fj ) · cj−1 + σ(ij ) · tanh(gj )h˜j = σ(oj ) · tanh(cj )−→hj = h˜j , j ∈ [1, T ]←−hj = h˜j , j ∈ [T, 1]−→ ←−hj = [hj , hj ]

(2)

(3)
(4)
(5)
(6)

where W wh ∈ R4H∗E , W we ∈ R4H∗H , bwh ∈ R4H are weight parameters. The σ and tanh arerespectively a sigmoid function and a hyperbolic tangent function.
3.3 Word attention layer
Recently, attentive neural networks have shown success in several NLP tasks such as machine translation(Bahdanau et al., 2014), image captioning (Xu et al., 2015), speech recognition (Chorowski et al., 2015)
and document classification (Yang et al., 2016).
We introduced an attention mechanism (Yang et al., 2016) into the proposed network to extract words
that are important to capture the meaning of the sentence. The network outputs the hidden sentence
vector mi in the following equations.
uj = tanh(W a hj + ba )(7)

exp(uTj ua )aj = ∑
T
j exp(uj ua )

(8)

mi =

∑

aj hj

(9)

j

where W a ∈ R2H∗H , ba ∈ R2H , ua ∈ RH are weight parameters.
The network predicts attribute label vi and condition label ci for the sentence, given the hidden sentence vector mi as input.
p(vi |mi ) = sof tmax(W v mi + bv )(10)p(ci |mi ) = σ(W c mi + bc )(11)

where W v ∈ RV ∗H , bv ∈ RH , W ci ∈ RV ∗H , bc ∈ RH are weight parameters.
The cost function L is the negative log-likelihood as the following equation:
L=−∑(log p(vˆi |mi ) + log p(cˆi |mi ))iwhere vˆi is the true attribute label and cˆi is the true condition label for the i-th sentence.

25

(12)

3.4

Sentence encoder

Given a document, the sentence encoder considers a sentence sequence as input to capture semantic representations of sentence sequential data. All sentences are encoded into sentence vectors{s1 , s2 , · · · , sL }.
The network takes a bag of words vector bwi , one-hot vector of HTML tag ti and the output vectorsof the word attention layer: p(vi |mi ) and p(ci |mi ) for the i-th sentence as input.
si = W semb [bwi , ti , p(vi |mi ), p(ci |mi )] + bsemb

(13)

t

where W semb ∈ R(|V |+|V |+|v|+|c|)∗H , bsemb ∈ RH are weight parameters and |V t | is the size of theHTML tag vocabulary. |v| and |c| are respectively the number of labels for attributes and conditions.
Then, the network outputs vectors {h1 , h2 , · · · , hL } as the following equations, given a sentence embedded vector sequence {s1 , s2 , · · · , sL }.




fl
 i 
 l 

 = W wh hl−1 + W we et + bwh
 ol 
gl(14)

ct = σ(fl ) · cl−1 + σ(il ) · tanh(gl )(15)hl = σ(ol ) · tanh(cl )(16)

where W wh ∈ R4H∗H , W we ∈ R4H∗H , bwh ∈ R4H are weight parameters.
3.5 Output layer
The output layer predicts the attribute label Vi and the condition label Ci in a way similar to that of theword attention layer.
p(Vi |hi ) = sof tmax(W V hi + bV )(17)
vs = argmaxVi p(Vi |hi )(18)p(Ci |hi ) = σ(W C hi + bC )(19)

where W V ∈ RV ∗H , bV ∈ RH , W C ∈ RV ∗H , bc ∈ RH are weight parameters.
The cost function L is the negative log-likelihood as the following equation:
L=−∑(log p(vˆi |hi ) + log p(cˆi |hi ))

(20)

i

4

Experiments

4.1 Data set
To evaluate the proposed network, we utilized two domain document sets: seven insurance productleaflets (4,695 sentences) and 44 Wikipedia documents (2,655 sentences) about Kamakura, a famoussightseeing place in Japan. All documents are written (in Japanese) in HTML format.
Each sentence in the documents is annotated with labels that represent the value of pre-defined attributes and conditions as determined by an expert. For example, the sentence ”Special contract forindividual” is labeled as the value of attribute ”special contract” and as condition.
We defined 37 attributes for insurance domain, such as ”Special contract”, ”Reasonable cause forpayment”, ” No reasonable cause for payment” and ”NIL” and 27 attributes for tourism domain, suchas ”Overview”, ”Origin of the name”, ”Famous product” and ”NIL” .

26

4.2 Experimental settings
We evaluated the quality of information extraction by judging whether the extracted values matched
the annotated labels, excluding the ”NIL” label which means that the sentence cannot be represented
as pre-defined attributes. We defined the correct values as those for which the annotated labels of thesentence include the extracted values of attributes except the ”NIL” label. We used a micro-averaged
F1 score as the evaluation metric for the seven insurance domain documents by applying leave-one-out
cross-validation and for the 44 tourism domain documents by applying 10 fold cross-validation.
A comparison of our method with other methods follows.
• Baseline MaxEnt: This is a method using a maximum entropy model that selects the |V | mostfrequent words from the training dataset and uses the count of each word as features. We consider
this to be the baseline method for classifying a sentence into value and condition classes using
simply words as input features.
• (proposed) HN: This is a method using the hierarchical network described in Section 3. The
network captures semantic representations of word- and sentence- sequential data and classifies
each sentence in a document into attributes and condition classes.
• HN-word:
This is a method using a network that has the same architecture as the proposed
network but has no output layer or sentence encoder. The network takes only the word-sequential
information as input features to classify a sentence into value and condition classes. We used thismethod to evaluate the effects of using sentence-sequential information to classify a sentence.
• HN-sent: This is a method using a network that has the same architecture as the proposed network
but has no word encoder or word attention layer. The network ignores the word-sequential information and uses the count of each word as features in classifying a sentence into value and condition
classes. We used this method to evaluate the effects of using word-sequential information and an
attention mechanism to classify a sentence.
4.3 Model parameters
The hyper parameters of the models for the four methods above were tuned experimentally. In our
experiments, we set the word embedding dimension E to be 100 and hidden layer dimension H to be
200. The size of the vocabulary for words V and HTML tags V t respectively are set to be 4000 and 50.
We selected words in the vocabulary as V words of the highest frequency in all datasets.
We used Chainer (Tokui et al., 2015), a framework of neural networks, for implementing our architecture. We used Adadelta (Zeiler, 2012) to train all models and a mini-batch size of 32. In total, 20 training
epochs were used.
4.4 Results
Table 1 shows micro-averaged precision, recall, and F1 scores for the test dataset when each method wastrained with a train dataset. The F1 scores seemed to be generally low as classification tasks since weignored the ”NIL” label, which accounts for about 60% of the total dataset. These scores were used toevaluate the quality of information extraction.
Method HN, the use of the proposed network, achieved the best F1 values in both the insurance andtourism domains and performed statistically significantly better than the baseline method MaxEnt in allof the experiments. Except for condition classification results in the tourism domain, methods HN-sent
and HN performed significantly better than methods MaxEnt and HN-word. These results shows that
sentence-sequential information is effective in classifying sentences into attribute and condition classes.
Table 2 shows some examples classification results for each method. It can be seen that some sentences
in a listing structure were classified into the same attribute class ”No reasonable cause for payment”
correctly by methods HN-sent and HN. This is because they capture semantic representation of sentencesequential data and thus classified sentences in a listing structure that are close in meaning into thesame class ”No reasonable cause for payment”. On the other hand, MaxEnt and HN-word, which27

domaininsurance

tourism

methodMaxEnt (baseline)
HN-word
HN-sent
HN
MaxEnt (baseline)
HN-word
HN-sent
HN

P
0.504
0.537
0.592
0.611
0.436
0.443
0.556
0.562

Attribute
RF1
0.463 0.483
0.461 0.496∗∗
0.564 0.578∗∗
0.582 0.596∗∗,†0.293 0.350
0.320 0.371∗∗
0.438 0.490∗∗
0.459 0.505∗∗

P
0.227
0.406
0.461
0.455
0.500
0.652
0.650
0.667

Condition
R
F1
0.344 0.274
0.301 0.346∗∗
0.291 0.357∗∗
0.328 0.381∗∗,†
0.382 0.433
0.417 0.509∗
0.361 0.464
0.444 0.533∗∗

Table 1: Micro-averaged F1 scores for test datasets. Asterisks mean there is a significant difference
between the F1 score obtained for the method indicated and the F1 score obtained for the baseline
method. Daggers mean there is a significant difference between the F1 score obtained for the method
and the next largest F1 score obtained for another method. (*,†: p < .05 , **: p < .01)
HTML
tag
<h3>
<h4>
<li>
<li>

<li>

<li>

Sentence

MaxEntPredicted label
HN-word
HN-sent

HN

Correct label

Reason for not paying benefits(the primary contract)
State of health differs from that reported.
Hospitalization due
to injury caused before indemnity period.
Hospitalization forreasons other thantreatment / unnecessary hospitalization.
Check policy summary for details.

NIL

NIL

NIL

NIL

NIL

NIL

NIL

NIL

NIL

NIL

No reasonablecause for payment
Reasonable
cause
for
payment

No reasonablecause for payment
Reasonable
cause
for
payment

No reasonablecause for payment
No reasonablecause for payment

No reasonablecause for payment
No reasonablecause for payment

No reasonablecause for payment
No reasonablecause for payment

Reasonable
cause
for
payment

Reasonable
cause
for
payment

Reasonable
cause
for
payment

No reasonablecause for payment

No reasonablecause for payment

NIL

NIL

NIL

NIL

NIL

Table 2: Example classification results for each method
ignore the sentence-sequential information, incorrectly classified such sentences into the attribute class”Reasonable cause for payment”. The reason for these results is that the word information for thesesentences is not sufficient for classifying the sentences into the correct attribute classes.

5

Conclusion

This paper described a hierarchical neural network for extracting structured data from product descriptions. The network classifies each sentence into attribute and condition classes jointly in two steps on thebasis of word sequences and sentence sequences in the document. First, the network obtains sentence
semantics by aggregating important words into sentence vectors. Then it classifies each sentence intopre-defined attribute classes and condition classes incorporated with sentence sequences.
Experimental results demonstrated that the method using the proposed network significantly outperformed baseline methods by taking semantic representation of word and sentence sequential data into
account. We found that sentence-sequential information was effective in extracting sentence-level values of product attributes from web documents while word information was insufficient for extracting
sentence-level values.
To obtain concrete information that can be used in question answering systems, it is helpful to extract relational information between attribute value and condition sentences. Addressing the problems
involved in extracting relationships between sentences remains as a subject for our future work.

28

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