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
Copyright
c
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
T
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.
REFERENCES
Navrro, A., Sierra, J-L., Fernandez-Manjon, B.,
Fernandez-Valmayor, A, 2000. XML-based
Integration of Hypermedia Design Component-Based
Techniques in the Production of Educational
Applications. In: Manuel Ortega, José Bravo (eds.)
Computers and Education in the 21st Century, Kluwer
2000.
Buendia, F., Diaz, P., Benlloch, J. V., 2002. A Framework
for the Instructional Design of Multi-Structured
Educational Applications. In: P. Barker & S.
Rebelsky, Eds., Proceedings of World Conference on
Educational Multimedia, Hypermedia and
Telecommunications 2002, Chesapeake, VA, 210-215.
Chang-xin, S., Qinghai, K. M., 2008. Applications of
Data Mining in the Education Resource Based on
XML, In Advanced Computer Theory and
Engineering, 2008. ICACTE '08 International
Conference, 20-22 Dec. 2008, pp. 943 - 946
Extensible Markup Language (XML) 1.0 (3rd ed.), 2010.
http://www.w3.org/TR/REC-xml/, retrieved on
September 20, 2010.
Cascading Style Sheets, 2010 http://www.w3.org/Style/
CSS/ retrieved on September 20, 2010.
XSL Transformations (XSLT)W3C Recommendation;
http://www.w3.org/TR/xslt, retrieved on September
20, 2010.
XPath, 2010, http://www.w3.org/TR/xpath/, Retrieved on
September 20, 2010.
Müldner, T., Wong, F., Benoit, D., 2004. My Webpage
can Speak Many Languages. In ED-Media 2004,
Lugano, Switzerland, 2004. AACE Proceedings, pp.
2040-2046.
Müldner, T., Fry, C., Miziołek, J. K., Corbin, T., 2010.
Updates of Compressed Dynamic XML Documents.
In The Eighth International Network Conference
(INC2010), Heidelberg, Germany, July 2010.
UPDATEABLE EDUCATIONAL APPLICATIONS BASED ON COMPRESSED XML DOCUMENTS
371