ravisupreme

Automated Online News Classification with

Personalization

Chee-Hong Chan Aixin Sun Ee-Peng Lim

Center for Advanced Information Systems, Nanyang Technological University

Nanyang Avenue, Singapore, 639798

Abstract

Classification of online news, in the past, has been very much done in the manual
way. In the Categorizor system, we have experimented an automated approach to

classify online news using the SVM (Support Vector Machine) classification method.
SVM has been shown to give good classification results when ample training doc-
uments are given. In our research, we have applied the SVM classification method

to personalized classification. In personalized classification, users can define their
personalized categories using a few keywords. By constructing search queries using
these keywords, the Categorizor obtains both positive and negative training doc-

uments required for the construction of classifiers. In this paper, we describe the
preliminary version of the Categorizor and present its system architecture.

1 Introduction

1.1 Motivation

Text classification is the process of assigning text documents to one or more predefined

categories based on their content. This allows users to find desired information faster

by searching only the relevant categories and not the whole information space. The

importance of text classification is even more apparent when the information space is

huge such as the World Wide Web. Web classification services provided by web portals

such as Yahoo![15] and Google[7] represent an approach to classify web sites and pages.

As such classification services are being carried out by human experts, they do not scale

up well with the growth rate of web pages on the Internet. To automate the classification

process, machine learning methods have been introduced. In a text classification method

based on machine learning, one or more classifiers is built (trained) with a given set of

training documents. The purpose of a trained classifier is therefore to assign documents

to the suitable categories with minimal human intervention.

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Online news articles represent a type of web information that are frequently referenced

and are mostly textual. Currently, online news are provided by many dedicated newswires

such as Reuters[11] and PR Newswires[10]. These newswires may specialize in reporting

news in different areas (e.g. financial, sports). It would be useful to gather news from

these sources and classify them accordingly for ease reference.

In this paper, we describe a working news classification system, named Categorizor[1],

that performs automated online news classification. The Categorizor attempts to adopt

the Support Vector Machine(SVM) to classify news articles into several general categories

and special categories defined by the users. The latter are also known as the personalized

categories. With personalized categories, the Categorizor allows users to quickly locate

the desired news articles with minimum effort.

1.2 Related Work

Text classification has been a well studied problem. Several methods have been proposed

previously and many of them can be directly applied to news classification as long as

the categories are predefined and there exists a good set of training documents for each

category[17, 6, 14]. Nevertheless, when the categories (i.e., personalized categories) are

defined on the fly and training documents are not readily available, the classification

problem will become much more complex. Text classification with user-defined or per-

sonalized categories is a form of personalization and there are several existing ways to

support personalization.

In the collaborative filtering approach, each user is associated with a user profile.

When the user profiles of two users are similar, news articles read by one of them will be

automatically recommended to the other[2].

In another personalization approach known as content filtering, one or more set of

features each representing a different interest domain (personalized category) of the user is

derived. News articles are then recommended based on the semantic similarity with each

set of features. In this approach, the interest domain of a user is very much independent

of that of another user.

In the subscription-based personalization approach, a user can manually subscribe to a

subset of a large number of pre-defined news categories. The set of pre-defined categories

is usually static and it corresponds to the categories assigned to the news article when

they are first created. In other words, the subscription-based personalization approach is

rather straightforward and does not require much classification efforts. Most of the web

sites achieve news personalization by adopting the subscription approach, e.g. Newscan-

online [9, 4].

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Among the above three approaches, we have chosen to use content filtering approach

to support personalized categories in the Categorizor system. However, there two main

difficulties in using this approach for personalized news classification. Firstly, it is not

easy to obtain the training documents required for the generation of classifiers. As news

articles are generally short, the selection of features for classification will become more

important than that in normal text classification problem.

2 The Categorizor

2.1 General Features

At present, the Categorizor is developed to classify mainly financial news. It offers

two kinds of classification, namely, the general classification and personalized classifica-

tion. In general classification, we have adopted a fix set of categories from the Reuters

collection[12]. The Reuters collection was chosen because its categories are closely re-

lated to financial services and economics. For a start, we have designed the Categorizor

to classify news articles from the Channel News Asia [3]. A classifier is developed for

each category using the corresponding Reuters training documents.

The unique feature of the Categorizor is that it allows users to create and maintain

their own personalized categories. Users can register with the Categorizor and subse-

quently create a personalized news categories by specifying a few keywords associated

with the category. There is no restriction on the number of personalized categories for

each user. To build the classifier for a personalized news category, a number of training

documents (news articles) have to be obtained. Instead of getting the user to perform

the time-consuming task selecting and uploading the training documents, we construct a

query to the Yahoo News Search Engine[16] using the user supplied keywords for the cat-

egory. The training documents are then selected from the most highly ranked resultant

news articles from Yahoo news.

To cope with evolving user interests and to further improve the effectiveness of clas-

sifiers for personalized categories, our personalized classifiers are defined such that they

can be retrained upon user request. The retraining of the personalized classifier can be

performed in two ways. The first involves redefining the keywords of the personalized

category. The other is to have the user providing feedback as he/she read the categorized

news. These new articles carrying feedbacks will be later used as training documents for

retraining the personalized classifiers.

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2.2 Architecture

User details Search Engine

Webpage Crawler

Text Extractor SVM Learn Module

Document Pre-processor

Document Vector Generator SVM Classify
Module

Result Interpreter

Display Formatter Database News Reuters Test
Collection Database System User Registration
Module HTTP
requests

News text (for
classification) (for training or
for classification) News webpages

News text
(for training) News text (for
classification)

News text document
vector (for classi-
fication) News text document
vector (for training) Prediction
file

Sorted classi-
fication results Training news articles
for personalized
categories WWW Webpage retrieval
Module

Presentation
Module SVM
Module Storage
Module

Preprocessing
Module query Search
results
Webpages

Pre-processed news text Model file Model file User details Yahoo! News

Figure 1: Architecture overview of the Categorizor

The architecture of the Categorizor is shown in Figure 1. The main architecture

consists of six modules, i.e. the Pre-processing, Presentation, Storage, SVM Classifier,

User Registration and Webpage Retrieval modules.

The Webpage Retrieval module employs the web page crawler to download the on-

line news articles from the Channel News Asia web site. The Pre-processing module

consists of the Text Extractor, Document Pre-Processor and the Document Vector Gen-

erator. The Text Extractor extracts the news text from the downloaded news pages. The

extracted news text for classification is stored in the News Database. The Document Pre-

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processor performs stop-word removal and word stemming on the extracted text. After

pre-processing, document vectors are generated by the Document Vector Generator using

the well known tf × idf scheme [13]. To cater for documents with varying length, the

document vectors are normalized to unit length.

There are three information repositories in the system. The News Database stores

the attributes of the news articles downloaded from the online news web sites for both

training (in the case of personalized classification) and classification. The attributes to be

stored include the downloading date, the URL and the news text. The System Database

holds information about users and their personalized categories.

The SVM Classifier is a binary classifier which consists of the SVM Learn Module and

the SVM Classify Module. The SVM Learn Module trains the classifier of a category

(general or personalized) and produces a model file. Given the model file, the SVM

Classify Module performs classification on a given set of documents (represented by their

document vectors). In our prototype system, the SV M light package developed by Joachim

is used [8].

The Presentation module sorts the classification results from SVM classifier according

to the score values returned by the SVM Classify Module. The User Registration module

is responsible for the management of user information and their personalized categories.

3 Classification Process

The Categorizor performs two kinds of classification as mentioned in Section 2.1. The

two kinds of classification are performed in different ways. The detailed classification

process are described in this section.

3.1 General Classification

In general classification, all the categories are taken from the Reuters-21578 text collec-

tion. Only 10 general categories are currently supported by the Categorizor and users

can select any general categories for viewing as shown in Figure 2. We build a SVM

classifier for each of the 10 categories as each SVM classifier is capable of giving a binary

decision given an input document. The steps of training and using a SVM classifier are

as follows:

1. The SVM classifier is trained with the training documents from the Reuters-21578

text collection. The positive documents are the ones that belong to the category

and equal number of negative training documents are randomly selected from the

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Figure 2: Selection of general categories

rest of categories. After training, the output of the SVM classifier (i.e. the model

files) are stored in the System Database.

2. The news articles are downloaded daily from the source website, (i.e. the Channel

News Asia news) and their text are extracted from the news bodies by the Text Ex-

tractor and then stored in the News Database. The text are referred as documents

in the later process.

3. When the user requests for the news from category C
i , the most recently downloaded

documents are retrieved from the News Database. Their document vectors are

generated by the Document Pre-processor and Document Vector Generator.

4. The model file for category C
i is retrieved from the System Database and the

corresponding SVM classifier will start classifying the document vectors.

5. The classification results are sorted according to the score values assigned by the

SVM classifier and displayed in the resultant web page as shown in Figure 3. In

the resultant web page, we use 5-point ranking to identify the relevance of the the

news articles to the category.

3.2 Personalized Classification

In personalized classification, the personalized categories are defined by users and each

category is described by a few keywords. The classification steps are as follows:

1. The user first registers his/her user name and password with the Categorizor.

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Figure 3: Results returned for general categories

2. The user defines his/her personalized categories by providing category names and

a set keywords for each personalized category that describe the content of the

category.

3. To obtain the training news articles (documents) for each personalized category, the

keywords are submitted to the Yahoo! news search engine and the news articles

originally from Reuters returned by Yahoo! are used as the positive training doc-

uments. The negative training documents are obtained by conducting an inverse

keyword search on the Yahoo news search engine. The inverse keyword search can

be easily achieved by adding a "-" operator before the keyword.

Figure 4: Entering keywords to define a new personalized category

4. All the positive and negative training news articles are submitted to the Text Ex-

tractor and the document vectors are generated with the Document Vector Gener-

ator.

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5. A SVM classifier is constructed by the SVM learn module for the each newly con-

structed personalized category. The learning process utilizes both the positive and

negative training document vectors. The generated classifier is stored as a model

file within the System Database.

6. When a user requests for news under his/her personalized category C
j , the recently

downloaded news from News Database are retrieved and their document vectors

are generated by the Document Vector Generator.

Figure 5: Classifier re-training

7. Both the document vectors and the model file for C
j are passed to the SVM Classify

module and the classification results sorted by score values are displayed in HTML

format. In the resultant web page, a "Relevant?" checkbox is associated with each

news entry, as shown in Figure 5, to allow feedback from the user.

3.3 Re-training of the Classifier

In order to strengthen the personalization aspect of the Categorizor, it is designed to

accept feedback from the user. The user, while reading news from a category can indicate

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if the content of the news article is relevant for the particular category by checking the

"Relevant?" box. When the "Update classifier with selected document(s)" button is

clicked, the corresponding classifier will be re-trained with a new training set that includes

the feedbacked documents. In this way, users can constantly refine the training sets for

their personalized categories with better accuracy. At present, we have not evaluated the

effect of re-training in personalized classification. Experiments to evaluate the different

ways of training will be covered in the future research.

4 Conclusion

We have designed and implemented a preliminary version of news classification system

based on the SVM classification technique. The system is capable of both general clas-

sification and personalized classification. Our preliminary experiments, not reported in

this paper, have shown that our system works well for the general classification while the

there are rooms for improvement for the personalized classification.

As the Categorizor is still in its development and enhancement stage, much work need

to be done to make it a full-fledge news classification system, particularly the personal-

ized classification feature. Firstly, we need to enhance the Categorizor with a complete

set of general categories. Due to the unavailability of a generic extraction software for ex-

tracting the desired news text from HTML web pages, Categorizor is currently restricted

to classifying news articles from Channel News Asia only. A complete version of the

Categorizor will have to incorporate an extraction facility that allows users to specify the

sources of news articles. We are currently conducting experiments to improve the perfor-

mance of personalized classification. For example, we are exploring the use of hierarchy

in personalized classification as it has been reported that hierarchical classification gains

better performance than the flat classification[5].

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