Timothy C. Bell

Timothy C. Bell
University of Canterbury | UC · Department of Computer Science and Software Engineering

About

137
Publications
48,616
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
6,633
Citations
Additional affiliations
April 1988 - present
University of Canterbury
Position
  • Professor

Publications

Publications (137)
Article
Full-text available
In this article we examine key issues and tensions for developing and specifying Computing-related elements of curricula design, particularly the role of Computer Science in the curriculum. The article is based on a series of discussions and analyses of curriculum design across various countries with different approaches and traditions of Computing...
Article
Full-text available
Increasing class sizes to gain economies of scale have resulted in less interaction between lecturers and students during lectures. This paper presented the results of a pilot study that set out to examine the use of applications on personally owned devices (APODs) to enhance student interaction, participation and engagement in large lectures. The...
Article
Full-text available
In this paper we have examined the position and roles of Computer Science in curricula in the light of recent calls for curriculum change and we have proposed principles and issues to consider in curriculum design as well as identifying priority areas for further research. The paper is based on discussions within and beyond the International Federa...
Conference Paper
Full-text available
The need to increase student engagement in large lectures has been addressed in a number of studies with this paper being one phase in an ongoing study into the use of applications on mobile devices to address this need. The purpose of this paper is to present the results of a focus group conducted with a group of students from two courses where an...
Conference Paper
Much of what we can do with Computer Science seems like magic, such as searching billions of items in a fraction of a second, or decrypting a secure message without needing to know the key that was used to encrypt it. Other parts are surprising — surely given a fast enough computer we can find the optimal solution to a problem? This paper investiga...
Conference Paper
Full-text available
We propose a root stemmer for the Modern Standard Arabic (MSA) language in an attempt to enhance the performance of Arabic Information Retrieval (AIR). The new Simple Ara- bic Stemmer (SAS) is based on the Quran morphology, since the Quran was a key source for the derivation of Arabic mor- phological rules. The stemmer is developed by decomposing a...
Article
For many years computing in New Zealand schools was focused on teaching students how to use computers, and there was little opportunity for students to learn about programming and computer science as formal subjects. In this article we review a series of initiatives that occurred from 2007 to 2009 that led to programming and computer science being...
Article
Providing students, teachers, and parents with a better understanding of computer science and programming.
Article
This paper focuses on pedagogy for teaching acceptance testing to high school students in the context of the new New Zealand computer science standards. A review of resources that are currently available for teaching acceptance testing to high school students shows a major gap. In order to bridge that gap we have identified and evaluated resources...
Article
Well-designed educational games (both online and offline) can be a valuable way to engage students with a topic. However, games can also be a time-consuming distraction, so it is useful to be able to identify which are suitable. This paper provides guidelines for evaluating games, and applies them to identify promising games. We begin by defining w...
Article
Computer science was progressively introduced as a subject in New Zealand high schools between 2011 and 2013, and teachers have played a key role in the success of the introduction of the new curriculum. This paper looks at how the process has worked from their point of view, primarily by comparing teacher responses to two surveys, one early in the...
Conference Paper
In 2011 New Zealand introduced computer science into high schools after a long period when computing was mainly focussed on training students to be users. The transition was rapid, and teachers had little time to upskill to prepare for the new topics, and yet there was widespread voluntary adoption of the new standards. The role of teachers and the...
Conference Paper
You've been asked to talk to an elementary or high school class about Computer Science, but how can you ensure that the talk is engaging? Or perhaps you're trying to introduce a concept from Computer Science to a school group, but you want a fun way to get the class engaged. This workshop is a hands-on introduction to Computer Science Unplugged (ww...
Conference Paper
Full-text available
In 2011 New Zealand introduced computer science as a topic that students could take as part of their studies in the last three years of high school. The change was initiated in late 2008, so the new material was introduced with barely two years of preparation and minimal teacher training. Despite this tight timeline, many schools adopted the new to...
Article
Outreach activities including Computer Science Unplugged demonstrate computer science concepts at schools and public venues based around kinesthetic activities rather than hands-on computer use. Computer Science Unplugged is a global project that has shared many such activities for children to adults using no technology, including how binary number...
Article
Computer science became available as a nationally assessed topic in NZ schools for the first time in 2011. We review the introduction of computer science as a formal topic, including the level of adoption, issues that have arisen in the process of introducing it, and work that has been undertaken to address those issues.
Article
You've been asked to talk to an elementary or high school class about Computer Science, but how can you ensure that the talk is engaging? Or perhaps you're trying to introduce a concept from Computer Science to a school group, but you want a fun way to get the class engaged. This workshop is a hands-on introduction to Computer Science Unplugged (ww...
Conference Paper
Mathematics popularization is an important, creative kind of research, entangled with many other research programs of basic interest — Mike Fellows This chapter is a history of the Computer Science Unplugged project, and related work on math and computer science popularization that Mike Fellows has been a driving force behind, including MEGA-Mathem...
Article
TR-COSC 07/01 This paper provides a survey of techniques for pattern matching in compressed text and images. Normally compressed data needs to be decompressed before it is processed, but if the compression has been done in the right way, it is often possible to search the data without having to decompress it, or at least only partially decompress i...
Article
Most data that is inherently discrete needs to be compressed in such a way that it can be recovered exactly, without any loss. Examples include text of all kinds, experimental results, and statistical databases. Other forms of data may need to be stored exactly, such as images—particularly bilevel ones, or ones arising in medical and remote-sensing...
Conference Paper
Formal Computer Science curricula in schools are currently in a state of flux, yet there is an urgency to have school students exposed to CS concepts so that they can make informed decisions about career paths. An effective way to address this is through outreach programmes that can operate outside or in conjunction with the formal education system...
Conference Paper
We examine five outreach programmes that introduce school students to Computer Science. All downplay programming as a pre-requisite skill for engaging with Computer Science, yet they use a wide variety of formats for reaching students, including contests, shows, magazine articles, and resources for teachers. We classify these different approaches,...
Article
This paper describes the design, implementation, and evaluation of a course teaching Computer Science majors about teaching Computer Science. The course was designed to address the need for teachers and resources to support rapid changes in topics being taught in high schools. It also helped prepare students for research in Computer Science Educati...
Article
This paper offers an exercise for revisiting the main sorting algorithms after they have been taught to students. This is done in a way that emphasizes the relationships between them, and shows how considering abstraction and extreme cases can lead to the generation of new algorithms. A number of authors (including textbook authors) have noted part...
Conference Paper
Full-text available
The Virtual Worlds Working Group began with the DEHub research consortium in November 2009. In December 2010, New Zealand joined the VWWG. This paper highlights the current work of the NZ based members of the group and presents the work of 23 authors at 11 institutes of higher education in New Zealand. The scope of the work covered is diverse, and...
Article
Full-text available
This paper examines implementing common computer science problems in Alice and Scratch.
Conference Paper
Full-text available
Despite several well-received designs for Computer Science curricula in secondary education being published both on national and international level, the implementation of these curricula is still being impeded by a variety of factors. This panel is intended to present issues, and approaches to solving them, from an international perspective. The p...
Chapter
The increasing popularity of Internet services such as the Amazon Web Services, Google App Engine and Microsoft Azure have drawn a lot of attention to the Cloud Computing paradigm. Although the term “Cloud Computing” is new, the technology is an extension of the remarkable achievements of grid, virtualization, Web 2.0 and Service Oriented Architect...
Conference Paper
Data hiding in computer system is an interesting and important research issue, which brings benefits for secret communication and watermarking. The development of virtual machine brings new potential for data hiding. In this paper we explore the potential for data hiding in virtual machine disk images, and especially hiding schemes that can be used...
Chapter
With cloud computing growing in popularity, tools and technologies are emerging to build, access, manage, and maintain the clouds. These tools need to manage the huge number of operations within a cloud transparently and without service interruptions. Cloud computing promises lower costs, faster implementation, and more flexibility using mixtures o...
Article
Full-text available
The New Zealand Ministry of Education has recently released a new "Digital Technologies" proposal for delivering computing topics in the final three years of High Schools. The proposal aims to address a number of issues by offering topics that will be academically challenging for students, and provide them with a broader view of the kinds of advanc...
Conference Paper
We describe the experiences of three University projects that use a style of physical, non-computer based activity to enthuse and teach school students computer science concepts. We show that this kind of activity is effective as an outreach and teaching resource even when reused across different age/ability ranges, in lecture and workshop formats...
Conference Paper
eLearning is an effective medium for delivering knowledge and skills to scattered learners. In spite of improvements in electronic delivery technologies, eLearning is still a long way away from offering anything close to efficient and effective learning environments. Much of the literature supports eLearning materials which embed simulation will im...
Conference Paper
Full-text available
"Computer Science (CS) Unplugged" is an educational method for introducing non-specialists to concepts of CS through hands-on activities that don't require the use of a computer. Often the deeper concepts of CS have been considered as being too difficult for elementary and middle school students, and many educators teaching "IT" are not even aware...
Conference Paper
This extended abstract describes a digital music stand integrated with the Greenstone digital library software. It features text annotation and an animated fast-to-slow page wipe. Figure 1 illustrates both these features, although it is best appreciated in a live demonstration. Digital annotation provides a non-destructive alternative to a musician...
Article
Full-text available
The Computer Science Unplugged project provides ways to expose students to ideas from Computer Science without having to use computers. This has a number of applications, including outreach, school curriculum support, and clubs. The "Unplugged" project, based at Canterbury University, uses activities, games, magic tricks and competitions to show ch...
Conference Paper
The rapid rate of the development of computer technology raises the issue of how to reform Computer Science education in elementary and middle schools. In Korea the government has taken this issue seriously, and the Ministry of Education & Human Resources Development has announced substantial revisions to its computing curricula, leading to a new c...
Book
This book will serve as a reference for seasoned professionals or researchers in the area, while remaining accessible for senior undergraduate students or first year graduate students embarking upon research in compression, pattern matching, full text retrieval, compressed index structures, or other areas related to the BWT. Key features include a...
Chapter
The Burrows-Wheeler Transform performs a permutation of the input string, and thus provides no compression on its own. Rather, the BWT essentially reorganizes the input sequence so that symbols with similar contexts are clustered together in the output stream. In this sense the BWT can be seen as a preprocessing scheme to expose potential redundanc...
Chapter
A fundamental operation with strings is determining whether a pattern of characters or symbols occurs as a substring in a larger string called the text, or as an approximate subsequence in the text. This problem has been investigated since the early 1960s, not only for its theoretical importance in computer science but because it has many applicati...
Chapter
The Burrows-Wheeler Transform has a very close relationship with suffix trees and suffix arrays — the array of indexes to the sorted array of substrings generated during the transform is essentially a suffix array, which in turn is a representation of the information in a suffix tree. As pointed out by Burrows and Wheeler in their original work (Bu...
Chapter
Through this book we have covered many of the directions that the BWT has led people in: new algorithms and data structures for performing the transform, fine-tuning the coding that can be done with the transformed file, new ways to sort the strings for the transform, a better understanding of other compression methods by relating them to the BWT,...
Chapter
This puzzle is an example of the Burrows-Wheeler Transform (BWT), which uses the intriguing idea of muddling (we prefer to call it permuting) the letters in a document to make it easier to find a compact representation and to perform other kinds of processing. What is amazing about the BWT is that although there are 2,615,348,735,999 different ways...
Chapter
Traditionally the major application of the Burrows-Wheeler Transform has been for data compression and efficient storage, and earlier chapters in this book have provided a detailed consideration of the BWT from this viewpoint, analyzing its performance for data compression. However, recent research on the Burrows-Wheeler Transform has shown the ver...
Chapter
This chapter will look in detail at how the Burrows-Wheeler Transform is implemented in practice. The examples given in Chapter 1 overlooked some important practical details — to transform a text of n characters the encoder was sorting an array of n strings, each n characters long, and the decoder performed n sorts to reverse the transform. This co...
Chapter
Like most transforms, the Burrows-Wheeler Transform does not change the size of the file that has been transformed, but merely rearranges it so that it will be easier to represent it compactly. It then needs to be coded using a second phase which we will refer to as the “Local to Global Transform” (LGT). Figure 3.1 shows a section of the transforme...
Chapter
With the huge excitement that was generated by the publication of the original paper on the Burrows-Wheeler Transform in 1994, followed by a more detailed empirical study by Fenwick between 1995 and 1996 (Fenwick, 1995b,c, 1996a,b), it did not take long before researchers started considering different variations, extensions and generalizations of t...
Conference Paper
Effective shape-based image retrieval requires an appropriate representation of object shape contours. Such a representation should be invariant under certain transformations, such as those due to rotation, scaling, partial occlusion, noise in the image, or changes in the viewing geometry. Given a shape boundary, we decompose it into primitive shap...
Conference Paper
Full-text available
Groupware communicates by sending messages across the network, and groupware programmers use a variety of formats for these messages, such as XML, plain text, or serialized objects. Although these formats have many advantages, they are often so verbose that they overload the system's network resources. Groupware programmers could improve efficiency...
Conference Paper
Full-text available
Moment functions have been used recently to compute stroke parameters for painterly rendering applications. The technique is based on the estimation of geometric features of the intensity distribution in small windowed images to obtain the brush size, colour and direction. This paper proposes an improvement of this method, by additionally extractin...
Article
Full-text available
Digital libraries and search engines are now well-equipped to find images of documents based on queries. Many images of music scores are now available, often mixed up with textual documents and images. For example, using the Google “images” search feature, a search for “Beethoven” will return a number of scores and manuscripts as well as pictures o...
Article
Recently a number of algorithms have been developed to search files compressed with the Burrows-Wheeler Transform (BWT) without the need for full decompression first. This allows the storage requirement of data to be reduced through the exceptionally good compression offered by BWT, while allowing fast access to the information for searching by tak...
Conference Paper
Full-text available
A personal digital music library needs to be ìagileî, that is, it needs to make it easy to capture and index material on the y . A digital camera is a particularly effective way of achieving this, but there are several issues with the quality of the captured image, including distortions in the shape of the image due to the camera not being aligned...
Article
Full-text available
This paper investigates attributes of the electronic dis- play of sheet music necessary for the development of a digital music stand. We explore the two conicting goals of minimising page turning effort and maximising the read- ability of images by conducting two user experiments. In our rst experiment participants trialed various page turn- ing me...
Conference Paper
Summary form only given. The approximate pattern matching on the text transformed by the Burrows-Wheeler transform (BWT) was considered. This is an important first step towards developing a compressed pattern matching algorithm for the BWT based compression system. Algorithms are proposed to solve the K-mismatch problem. Tests were performed on dif...
Article
Modern cryptography can achieve levels of security and authentication that non-specialists find literally incredible. Techniques including information-hiding protocols, zero-knowledge proofs and public key cryptosystems can be used to support applications like digital signatures, digital cash, on-line poker and secure voting in ways that are provab...
Article
The compressed pattern matching problem is to locate the occurrence(s) of a pattern P in a text string T using a compressed representation of T , with minimal (or no) decompression. In this paper, we consider approximate pattern matching directly on Burrow-Wheeler transformed (BWT) text which is a critical step for a fully compressed pattern matchi...
Article
Optical music recognition (OMR) systems are used to convert music scanned from paper into a format suitable for playing or editing on a computer. These systems generally have two phases: recognizing the graphical symbols (such as note-heads and lines) and determining the musical meaning and relationshipsof the symbols (such as the pitch and rhythm...
Conference Paper
This paper explores two techniques for on-line exact pattern matching in files that have been compressed using the Burrows-Wheeler transform. We investigate two approaches. The first is an application of the Boyer-Moore algorithm (1977) to a transformed string. The second approach is based on the observation that the transform effectively contains...
Conference Paper
Summary form only given. The compressed pattern matching problem is to locate the occurrence(s) of a pattern P in a text string T using a compressed representation of T, with minimal (or no) decompression. The BWT performs a permutation of the characters in the text, such that characters in lexically similar contexts will be near to each other. The...
Article
Full-text available
We investigate off-line dictionary oriented approaches to DNA sequence compression, based on the Burrows-Wheeler Transform (BWT). The preponderance of short repeating patterns is an important phenomenon in biological sequences. Here, we propose off-line methods to compress DNA sequences that exploit the different repetition structures inherent in s...
Article
This paper describes an improved design for pen input of music into a computer system. A usability analysis of an existing system is performed, and improvements based on the analysis are implemented and tested. New capabilities are also added. The resulting system is tested for both usability and speed of input, with good results in both areas. 1.
Article
Full-text available
This article describes the challenges posed by optical music recognition ‐ a topic in com- puter science that aims to convert scanned pages of music into an on-line format. First, the problem is described; then a generalised framework,for software is presented that emphasises key stages that must be solved: staff line identification, musical object...
Article
Full-text available
: Modern cryptography can achieve levels of security and authentication that non-specialists find literally incredible. Techniques include informationhiding protocols, zero-knowledge proofs and public key cryptosystems; they can be used to support applications like digital signatures, digital cash, on-line poker and secure voting in ways that are p...
Article
This correspondence considers the compression of matrices where the majority of the entries are a fixed constant (most typically zero), usually referred to as sparse matrices. We show that using Golomb or Rice encoding requires significantly less space than previous approaches. Furthermore, compared to arithmetic coding, the space requirements are...
Article
Named as one of 7 from the top 25 of the 115 full papers in the conference. Preparing courses for flexible delivery and distance education is normally a timeconsuming and expensive process. This paper describes the design and evaluation of a system that automatically captures and indexes audio and video streams of traditional university lectures wi...
Article
This paper discusses the teaching of Human-Computer Interaction (HCI) at opposite ends of the Computer Science course curriculum. We provide tips on course content within final-year HCI courses. These tips focus on interface dialogue notations which are often either ignored or superficially discussed in HCI texts. By teaching these notations throug...
Article
Full-text available
There is powerful evidence that office information systems and the information technology revolution are failing to deliver the expected productivity gains. Increased use of user-centred design and the associated methods and techniques of human-computer interaction (HCI) promise to improve an this poor performance. This paper demonstrates how empir...
Article
Preparing courses for flexible delivery and distance education is normally a time-consuming and expensive process. This paper describes the design and evaluation of a system that automatically captures and indexes audio and video streams of traditional university lectures without demanding any changes in the style or tools used by teachers. Using a...
Article
Full-text available
The complementary paradigms of text compression and image compression suggest that there may be potential for applying methods developed for one domain to the other. In image coding, lossy techniques yield compression factors that are vastly superior to those of the best lossless schemes and we show that this is also the case for text. This paper i...
Conference Paper
Science shows are commonly presented for the general public, and especially children, at science centres and festivals. Usually they use attention-grabbing experiments from the physical sciences, and the science of computing is absent from such presentations. This paper describes a series of demonstrations that present fundamental ideas from Comput...
Article
Full-text available
Data compression is well known as a transformation of data tra#c that is able to greatly increase the data rate in a network, and as the cost of processing power decreases compression is becoming more and more widely used for this purpose. In this paper, we look at the statistical properties of this transformation, studying changes in the probabili...
Article
Full-text available
. ?????????? 1 . INTRODUCTION Measurements of real data traffic have been widely recognized as an important aid in performance modeling, design and development of telecommunication networks. Newly emerging services and new applications of data communications demand more exhaustive measurement studies of data traffic to provide foundations for the d...
Article
Full-text available
Modern cryptography can achieve levels of security and authentication that non-specialists find literally incredible. Techniques include information-hiding protocols, zero-knowledge proofs and public key cryptosystems; they can be used to support applications like digital signatures, digital cash, on-line poker and secure voting in ways that are pr...