UPDATEABLE EDUCATIONAL APPLICATIONS BASED

ON COMPRESSED XML DOCUMENTS

Tomasz Müldner, Christopher Fry

Jodrey School of Computer Science, Acadia University, Wolfville, N.S., Canada

Jan Krzysztof Miziołek

IBI AL, University of Warsaw, Warsaw, Poland

Keywords: XML, Compression, Query, Update, Educational applications.

Abstract: Many recent educational applications, including stand-alone and client-server applications, use XML-based

data. Unfortunately, XML data are verbose, which results in large memory overhead and a low throughput

for network-based applications. In addition, most XML-based educational applications do not support an

essential feature, namely updates of data. In this paper we describe a specific type of XML compression and

outline its application to education. The use of the proposed approach will result in a new generation of

XML-based educational applications, which do not suffer from the afore-mentioned problems.

1 INTRODUCTION

A large number of educational applications (Navro

et al., 2000), (Buendia et al., 2002), (Song et al.,

2008) use the XML format (XML, 2010) for

underlying data. There are several reasons why

XML is a perfect choice for a data format. First,

XML is the de-facto standard for storing data, and

there are many tools (often available at no cost) to

process XML, such as XML parsers. Second, unlike

HTML, which provides only markups for format

specifications, XML provides structure for data. The

formatting of the data, be it PDF or HTML is left to

tools such as CSS (CSS, 2010) or even better XSLT

(XSL, 2010). Third, XML satisfies the need for

supporting internationalization of educational

applications, i.e. for making them available in

various languages without having to modify the

underlying data (Müldner, 2004). However, existing

applications suffer from two major problems, which

severely limit their usefulness. First, XML is

verbose and as a result, on average, XML-based

representation is often as much as 10 times larger

than the original data. This increase in size,

combined with a large amount of data to be

maintained, results in XML files that are hundreds of

megabytes in size. Specifically, some educational

applications (for example, a typical set of

courseware for an education institution) require

large amounts of data, consume vast amounts of disk

space, and cannot be used on increasingly more

popular wireless devices such as PDAs and mobile

phones. In addition, retrieval of any required data,

for example midterms used for a specific

courseware, will result in a query issued on the

underlying XML data, which will have a slow

response time. The second problem faced by XML-

based educational applications is that typically they

are static, i.e. they do not support updates of the

XML data (this limitation is caused by the fact that

currently most XML tools do not support updates).

However, the ability to update educational

applications is of paramount importance, for

example in order to modify a specific lesson or to

allow the instructor or the student to add notes or

bookmarks.

There is a considerable body of research on

XML data compression, and more recently on

queryable XML compression with lazy

decompression. At the same time, there is little

research on updateable XML compressors with lazy

decompression (Müldner, 2010). However, there is

no research known to the authors of this paper that

provides an indication as to how queryable and

updateable XML compression with lazy

369

Müldner T., Fry C. and Miziołek J..

UPDATEABLE EDUCATIONAL APPLICATIONS BASED ON COMPRESSED XML DOCUMENTS .

DOI: 10.5220/0003297203690371

In Proceedings of the 3rd International Conference on Computer Supported Education (CSEDU-2011), pages 369-371

ISBN: 978-989-8425-49-2

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

decompression may be used for educational

purposes. This paper attempts to fill in this gap and

it describes such a compressor and its applications to

education.

Contributions. The main contribution of this paper

is a description of an application for educational

purposes of a queryable and updateable XML

compressor, called XSAQCT.

This paper is organized as follows. Section 2

describes XSAQCT (Section 2.1) and then it

outlines the applications of XSAQCT for

educational purposes (Section 2.2). Section 3

provides conclusions and it describes our future

work.

2 XSAQCT AND ITS

APPLICATIONS

In this section, we briefly describe the architecture

of XSAQCT, and then outline its applications for

education.

2.1 Architecture of XSAQCT

In the first stage, we use a SAX-parser to separate

structure and contents. In addition, the structure is

summarized to provide a concise representation

amenable for querying and updates. Specifically,

given a document D, a single SAX traversal of D

creates an annotated tree T

A,D

, in which all similar

paths (i.e. paths that are identical, possibly with the

exception of the last component, which is the data

value) are merged into a single path. Every tree node

A,D

is labeled with an annotation representing

father-children relations via an integer sequence. For

a sample XML document shown in Fig. 1, the

corresponding XML tree and its concise

representation in the form of an annotated tree are

shown in Fig. 2.

The tree representing the structure summary in

XQueC, another well-known XML compressor, is

additionally annotated with indices into the array,

called ID sequences storing pairs of the form <path

from the structure summary, a list of pre/post order

numbers for each occurrence of the first element of

this path>. As a result, XQueC’s structure summary

is less compact than XSAQCT’s. For the sample

XML document shown in Fig. 2, annotations in

XSAQCT consist of 12 integers, while XQueC’s

structure summary requires 20 integers. This

difference in size is much more profound for very

large XML documents.

Figure 1: Sample XML document.

Figure 2: The XML document and its annotated tree.

In XSAQCT, data values are written to various

containers based on the rule that values belonging to

similar paths are written to the same container and

subsequently compressed.

Queries over XML data are implemented in

XSAQCT using a small subset of (XPath, 2010).

Our future work will extend this set.

Various update operations on the document D

are available.

2.2 Applications of XML Compression

to Education

In this section, we describe a typical educational

application and outline how XML compression can

be used to facilitate the implementation of such

application.

Consider an educational institution, which

maintains a set of courseware. Each courseware

consists of a number of lessons, and each lesson

consists of an optional pre-test, a number of pages,

and an optional post-test. In addition, we assume

that each page may have a number of notes

associated with this page (for example, storing

instructor’s suggestions as to what should be studied

CSEDU 2011 - 3rd International Conference on Computer Supported Education

370

more carefully, or student “to-do” lists).

The structure of courseware presented in Fig. 3

shows that it is well suited for compression with

XSAQCT, since as we noted before this compressor

has the best performance for regular structures.

Our previous experience with creating XML-

based courseware of the above type showed that the

user’s interface should provide the following

functions:

1. Author’s interface to support building the

initial courseware

2. Learner’s interface to support access to

specific courseware, or just specific lessons

or pages within the lesson

3. Author’s interface to support

insertion/deletion of new pages/lessons,

modifications of selected pages and

insertion/deletion/modification of author’s

notes

4. Learner’s interface to support

insertion/deletion/modification of learner’s

notes

In what follows, we outline a design of the

implementation of the above interface based on

XSAQCT used as an XML compressor.

Implementation of the author’s interface (point 1.

above) can use basic XML tools, such as XML

parsers. When the process of courseware creation is

completed, XML data created are passed on

XSAQCT for compression and storage.

Implementation of the learner’s interface listed in 2.

above uses standard queries, which will result in

partial decompression of the required courseware;

the entire courseware will continue to be saved in a

compressed form. Points 3. and 4. listed above will

be implemented via the update functionality of

XSAQCT with lazy decompression.

3 CONCLUSIONS

In this paper we showed how XML-based

educational applications can be implemented in

more efficient way using compressed XML

documents, which can be updated and queried with

minimal decompression. Our future work we will

design and test a more complete educational

application based on compressed XML data.

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