Tomasz Müldner

Hypermedia—introduction and survey

Abstract Our paper begins with an introduction to hypermedia presented with the example of a hypothetical hypermedia system. This is followed by an overview of the main hypermedia components visible to the user—data structures, authoring tools, navigation tools, and user interface. In the next section, we present a brief history of hypermedia, list applications in which hypermedia systems have been used, and describe several important commercial products and research projects. The last two sections introduce the major issues facing hypermedia technology and attempt to predict what direction it might take in the near future.

AXECHOP: a grammar-based compressor for XML

Summary form only given. XML is gaining widespread acceptance as a standard for storing and transmitting structured data. One of the drawbacks of XML is that it is quite verbose: an XML representation of a set of data can easily be ten times as large as a more economical representation of the data. To overcome this limitation, we present a compression scheme tailored specifically to XML named AXECHOP. The compression strategy used in AXECHOP begins by dividing the source XML document into structural and data segments. The former is represented using a byte tokenization scheme that preserves the original structure of the document (i.e. it maintains the proper nesting and ordering of elements, attributes, and data values). The MPM compression algorithm is used to generate a context-free grammar capable of deriving this original structure, and the grammar is passed through an adaptive arithmetic coder before being written to the compressed file. The documents data is organized into a series of containers (where container membership is determined by the identity of the XML element or attribute that encloses the data) and then the Burrows-Wheeler transform (BWT) is applied to the contents of each dictionary, with the results being appended to the compressed file.

Novel algorithm explanation techniques for improving algorithm teaching

The analysis and the understanding of algorithms is a very important task for teaching and learning algorithms. We advocate a strategy, according to which one first tries to understand the fundamental nature of an algorithm, and then---after reaching a higher level of awareness---chooses the most appropriate programming language to implement it. To facilitate the process of understanding of algorithms, their visualization, in particular animation, is considered to be the best approach. Traditional Algorithm Animation (AA) systems usually aim for teaching algorithms in higher education, see for example the chapter introduction of Kerren and Stasko [2002] or the earlier anthology on software visualization [Stasko et al. 1998].

Algorithm Explanation: Visualizing Abstract States and Invariants

Software visualization provides methods to facilitate the understanding of algorithms and programs. Practically all existing visualization systems actually execute the code to be visualized on sample input data. In this paper, we propose a novel approach to algorithm explanation based on static program analysis, specifically shape analysis. Shape analysis of a program operating on heap-based data structures analyzes the program to find out relevant properties of its heap contents. The shape analysis we are using is parameterized with sets of observation properties, which are relevant properties of heap elements. Shape analysis associates sets of shape graphs with program points. These graphs describe both structural properties and nonstructural properties such as sortedness. By summarizing sets of undistinguishable heap cells shape analysis supports focusing on active parts of the data structure. By computing the programs invariants it provides the basis for their visualization. After the application of the shape analysis the program is visually abstractly executed, i.e., traversed with a strategy corresponding to a meaningful explanation. Showing a sequence of shape graphs produced along a program path demonstrates how invariants are temporarily violated and then restored.

Web‐based Structured Hypermedia Algorithm Explanation system

Purpose – The purpose of this paper is to present the development of a system called Structured Hypermedia Algorithm Explanation (SHALEX), as a remedy for the limitations existing within the current traditional algorithm animation (AA) systems. SHALEX provides several novel features, such as use of invariants, reflection of the high‐level structure of an algorithm rather than low‐level steps, and support for programming the algorithm in any procedural or object‐oriented programming language.Design/methodology/approach – By defining the structure of an algorithm as a directed graph of abstractions, algorithms may be studied top‐down, bottom‐up, or using a mix of the two. In addition, SHALEX includes a learner model to provide spatial links, and to support evaluations and adaptations.Findings – Evaluations of traditional AA systems designed to teach algorithms in higher education or in professional training show that such systems have not achieved many expectations of their developers. One reason for this f...

Acadia Advantage—Evolution and Experiences

In 1996, Acadia University became the first Canadian university to adopt a plan of a fully computerized campus. This plan called for progressively equipping each student and faculty member with a personal laptop computer, introducing computer technology into most courses, providing students and faculty with ubiquitous access to the computer network everywhere on the campus, and integrating the technology into the undergraduate curriculum and campus life. In this paper, we describe the context in which this decision was made, discuss the nature of the experience and the involvement of faculty and students in the process, the logistic problems, and impact on faculty and students, successes and disappointments. We also present selected research projects undertaken by faculty within this framework, and outline plans for the future.

Parameterized Role-Based Access Control Policies for XML Documents

ABSTRACT Role-based access control policies (RBAC) are often used to provide access to fragments of static XML documents. Existing implementations of such RBACs often disseminate a single document encrypted with multiple cryptographic keys. However, most existing approaches are subject to role proliferation, especially in the case of large organizations where the number of defined roles may be several hundred. In such circumstances, correctly administering access control becomes much more difficult and error-prone. In this article, we present a novel approach to RBACs, which supports role parameterization to mitigate the potential of role proliferation. Our approach supports the association of specific user and/or session-specific credentials (i.e., parameters) with roles. We first define parameterized RBAC (PRABC), and then provide an algorithm for generating the minimal set of keys required to enforce a particular parameterized policy. We present another algorithm for efficiently encrypting an XML document in a single pass, using a technique that disguises the original structure of hidden subtrees. Finally, we include a key distribution algorithm that ensures each user receives only those keys that are needed for decrypting accessible fragments of the document. We analyze the complexity of our implementation and provide experiments to demonstrate its scalability.

PMS—A program to make learning Pascal easier

Abstract One of the essential tasks in the teaching of a programming language is the introduction of the main constructs of the language—the syntax and semantics of statements, control, procedures, file handling, and so on. Most teachers present this topic by simulating the operation of the computer on the chalkboard by manual tracing of the execution of sample demonstration programs. Upon closer inspection it becomes clear that this task could be performed by the computer itself. A program implementing this idea would help the teacher in the class and the student (who could use the computer to repeat the instructors performance at any time and on any problem of his choice) both in the class and in study. This article describes a collection of programs called PMS that performs exactly this function for the teaching of Pascal. PMS is organized as a collection of “mimlanguages” each of which demonstrates, and allows the user to experiment with, a certain category of Pascal features using a particular screen representation. Each of the subsystems contains a syntax-driven, screen-oriented translator associated with an interpreter that controls execution and the appropriate screen representation. This modular structure of PMS reflects the fact that programming is always taught by presenting certain essentially disjoint language features individually. In addition to their logical independence, these disjoint concepts also require different graphical approaches for their visual representation and this reinforces the need for modularization of the package. PMS is written in Pascal and runs on several computers including the IBM PC.

ATIA: algorithm teaching interface agent

This work presents an intelligent algorithm teaching interface agent (ATIA) that teaches algorithms. This agent is autonomous, goal-driven, dynamic and collaborative, and acts as a mediator between the student and the tutoring environment. It monitors the students habits and weaknesses to adapt its didactic directions based on his/her interests and preferences. This approach facilitates the reusability of this agent in different tutoring domains, such as iterative and recursive algorithms. ATIA offers to students a common, flexible and customizable interface that they can use for different algorithms. It explains an algorithm at various levels of abstraction. Each level is designed to present a single operation used in the algorithm. Operations are shown in a textual form of a pseudocode with an associated visualization. ATIA can make changes to the schedule of the algorithm lessons based on the students performance. To demonstrate and evaluate the feasibility of the proposed agent, we describe a prototype, which is being developed.

Parallelization of an XML data compressor on multi-cores

Because of a growing interest in using XML for massive complex data there has been considerable research on designing XML compressors. This paper presents our research aimed at building parallel XML compressors, using Java and OpenMP (with C++). Our findings show that OpenMP is a preferred choice achieving better results than Java using a multi-core platform.