User diversity and design representation: Towards increased effectiveness in Design for All

This paper addresses user modelling for “Design for All” in a model-based approach to Human-Computer Interaction, paying particular attention to placing user models within organisational role- and task-related contexts. After reviewing a variety of user modelling approaches, and deriving requirements for user modelling related to Design for All, the paper proposes a role-driven individualised approach. Such an approach is based on a model-based representation schema and a unifying notation that keeps the user’s models and the contextual information transparent and consistent. Individualisation is achieved by coupling symbolic model specifications with neural networking on synchronisation links between symbolic representation elements. As a result, user modelling for Design for All is achieved not by stereotypical user properties and functional roles, but by accommodating the actual users’ behaviour. Published online: 18 May 2001     

Whole-body modelling of people from multiview images to populate virtual worlds

In this paper a new technique is introduced for automatically building recognisable, moving 3D models of individual people. A set of multiview colour images of a person is captured from the front, sides and back by one or more cameras. Model-based reconstruction of shape from silhouettes is used to transform a standard 3D generic humanoid model to approximate a person's shape and anatomical structure. Realistic appearance is achieved by colour texture mapping from the multiview images. The results show the reconstruction of a realistic 3D facsimile of the person suitable for animation in a virtual world. The system is inexpensive and is reliable for large variations in shape, size and clothing. This is the first approach to achieve realistic model capture for clothed people and automatic reconstruction of animated models. A commercial system based on this approach has recently been used to capture thousands of models of the general public.     

A Framework for Integrating Non-Functional Requirements into Conceptual Models

The development of complex information systems calls for conceptual models that describe aspects beyond entities and activities. In particular, recent research has pointed out that conceptual models need to model goals, in order to capture the intentions which underlie complex situations within an organisational context. This paper focuses on one class of goals, namely non-functional requirements (NFR), which need to be captured and analysed from the very early phases of the software development process. The paper presents a framework for integrating NFRs into the ER and OO models. This framework has been validated by two case studies, one of which is very large. The results of the case studies suggest that goal modelling during early phases can lead to a more productive and complete modelling activity.       

Scenario Analysis in an Automated Tool for Requirements Engineering

 This paper presents an automated tool for scenario-driven requirements engineering where scenario analysis plays the central role. It is shown that a scenario can be described by three views of data flow, entity relationship and state transition models by slight extensions of classic data flow, entity relationship and state transition diagrams. The notions of consistency and completeness of a set of scenarios are formally defined in graph theory terminology and automatically checked by the tool. The tool supports automatic validation of requirements definitions by analysing the consistency between a set of scenarios and requirements models. It also supports automatic synthesis of requirements models from a set of scenarios. Its utility and usefulness are demonstrated by a non-trivial example in the paper. Case studies of the tools are also presented.     

Towards robust multi-cue integration for visual tracking

Abstract. Even though many of today's vision algorithms are very successful, they lack robustness, since they are typically tailored to a particular situation. In this paper, we argue that the principles of sensor and model integration can increase the robustness of today's computer-vision systems substantially. As an example, multi-cue tracking of faces is discussed. The approach is based on the principles of self-organization of the integration mechanism and self-adaptation of the cue models during tracking. Experiments show that the robustness of simple models is leveraged significantly by sensor and model integration.     

Multimedia network protocols: where are we?

Protocols for multimedia communication are needed to integrate into a single network services intended to satisfy the different requirements of multiple types of traffic. An essential prerequisite for designing these protocols is that the services to be offered by the network must be selected and specified in detail. We present the service models proposed, or being developed, by the Internet community, by the ATM community, and by the Tenet Group. We compare their common characteristics, which reveal the characteristics of the first integrated services networks are likely to offer. The services referred to in this paper are those at the network and transport layers, which support the services to be offered to the system's end users.     

Extending the Unified Modeling Language for ontology development

There is rapidly growing momentum for web enabled agents that reason about and dynamically integrate the appropriate knowledge and services at run-time. The dynamic integration of knowledge and services depends on the existence of explicit declarative semantic models (ontologies). We have been building tools for ontology development based on the Unified Modeling Language (UML). This allows the many mature UML tools, models and expertise to be applied to knowledge representation systems, not only for visualizing complex ontologies but also for managing the ontology development process. UML has many features, such as profiles, global modularity and extension mechanisms that are not generally available in most ontology languages. However, ontology languages have some features that UML does not support. Our paper identifies the similarities and differences (with examples) between UML and the ontology languages RDF and DAML+OIL. To reconcile these differences, we propose a modification to the UML metamodel to address some of the most problematic differences. One of these is the ontological concept variously called a property, relation or predicate. This notion corresponds to the UML concepts of association and attribute. In ontology languages properties are first-class modeling elements, but UML associations and attributes are not first-class. Our proposal is backward-compatible with existing UML models while enhancing its viability for ontology modeling. While we have focused on RDF and DAML+OIL in our research and development activities, the same issues apply to many of the knowledge representation languages. This is especially the case for semantic network and concept graph approaches to knowledge representations. Initial sbmission: 16 February 2002 / Revised submission: 15 October 2002 Published online: 2 December 2002     

Performability of disk-array-based video servers

Video services are likely to dominate the traffic in future broadband networks. Most of these services will be provided by large- scale public-access video servers. Research to date has shown that disk arrays are a promising technology for providing the storage and throughput required to serve many independent video streams to a large customer population. Large disk arrays, however, are susceptible to disk failures which can greatly affect their reliability. In this paper, we discuss suitable redundancy mechanisms to increase the reliability of disk arrays and compare the performance of the RAID-3 and RAID-5 redundancy schemes. We use cost and performability analyses to rigorously compare the two schemes over a variety of conditions. Accurate cost models are developed and Markov reward models (with time-dependent reward structures) are developed and used to give insight into the tradeoffs between system cost and revenue earning potential. The paper concludes that for large-scale video servers, coarse-grained striping in a RAID-5 style of disk array is most cost effective.     

Models in software engineering – an introduction

Modelling is a concept fundamental for software engineering. In this paper, the word is defined and discussed from various perspectives. The most important types of models are presented, and examples are given. Models are very useful, but sometimes also dangerous, in particular to those who use them unconsciously. Such problems are shown. Finally, the role of models in software engineering research is discussed. Received: 21 October 2002 / Accepted: 10 January 2003 Published online: 27 February 2003     

Embedding interactive sounds in multimedia applications

We describe a system for generating and controlling sound effects from within applications. We discuss performance demands and current technology constraints on sound synthesis methods, highlight several distinct interactive control strategies, and demonstrate a development environment for making a large database of heterogeneous sound models manageable by developers who are not sound synthesis experts.     

Coupling Use Cases and Class Models as a Means for Validation and Verification of Requirements Specifications

In many applications, especially from the business domain, the requirements specification mainly deals with use cases and class models. Unfortunately, these models are based on different modelling techniques and aim at different levels of abstraction, such that serious consistency and completeness problems are induced. To overcome these deficiencies, we refine activity graphs to meet the needs for a suitable modelling element for use case behaviour. The refinement in particular supports the proper coupling of use cases via activity graphs and the class model. The granularity and semantics of our approach allow for a seamless, traceable transition of use cases to the class model and for the verification of the class model against the use case model. The validation of the use case model and parts of the class model is supported as well. Experience from several applications has shown that the investment in specification, validation and verification not only pays off during system and acceptance testing but also significantly improves the quality of the final product.       

Range image segmentation using local approximation of scan lines with application to CAD model acquisition

Abstract. Automatic acquisition of CAD models from existing objects requires accurate extraction of geometric and topological information from the input data. This paper presents a range image segmentation method based on local approximation of scan lines. The method employs edge models that are capable of detecting noise pixels as well as position and orientation discontinuities of varying strengths. Region-based techniques are then used to achieve a complete segmentation. Finally, a geometric representation of the scene, in the form of a surface CAD model, is produced. Experimental results on a large number of real range images acquired by different range sensors demonstrate the efficiency and robustness of the method. Received: 1 August 2000 / Accepted: 23 January 2002 Correspondence to: I. Khalifa     

Efficient detection of discrepancies in multiple file copies

Summary. For data consistency in distributed information systems, it is often necessary to compare remotely located copies of a file. We develop several protocols for the efficient detection of differing pages in a replicated file in different communication and failure models. The first set of protocols assumes a restricted but practical communication model. In this case, the minimum amount of communication necessary to identify any given number of differing pages is determined and a technique to attain this minimum is presented. For the more general communication model and for more refined failure models, we show that more efficient protocols can be derived. Our approach is based on the theory of Galois fields. Received: February 1996 / Accepted: September 1997     

Effective timestamping in databases

Many existing database applications place various timestamps on their data, rendering temporal values such as dates and times prevalent in database tables. During the past two decades, several dozen temporal data models have appeared, all with timestamps being integral components. The models have used timestamps for encoding two specific temporal aspects of database facts, namely transaction time, when the facts are current in the database, and valid time, when the facts are true in the modeled reality. However, with few exceptions, the assignment of timestamp values has been considered only in the context of individual modification statements. This paper takes the next logical step: It considers the use of timestamping for capturing transaction and valid time in the context of transactions. The paper initially identifies and analyzes several problems with straightforward timestamping, then proceeds to propose a variety of techniques aimed at solving these problems. Timestamping the results of a transaction with the commit time of the transaction is a promising approach. The paper studies how this timestamping may be done using a spectrum of techniques. While many database facts are valid until now, the current time, this value is absent from the existing temporal types. Techniques that address this problem using different substitute values are presented. Using a stratum architecture, the performance of the different proposed techniques are studied. Although querying and modifying time-varying data is accompanied by a number of subtle problems, we present a comprehensive approach that provides application programmers with simple, consistent, and efficient support for modifying bitemporal databases in the context of user transactions. Received: March 11, 1998 / Accepted July 27, 1999     

Workflow Requirements Modelling Using XML

When modelling inter-organisational workflow it is important not to make assumptions such as with regard to the formats of the data exchanged between the workflow participants or the technical infrastructures and platforms, as they can restrict the range of possible workflow management implementations. The approach presented in this paper allows for the conceptual modelling of workflow processes using primitive constructs such as nodes, rules and business documents. The paper presents both a graphical notation for modelling workflows as well as a mapping of the workflow constructs to XML models that follows the Workflow Management Coalition interoperability standards. This allows the modelled workflow to be interpreted and executed by a variety of workflow engines.     

Patterns Approach to Product Information Systems Engineering

This paper deals with the application of the pattern approach to product information systems (PIS) engineering. Two kind of patterns are distinguished: business patterns used for specification and providing solutions for application field problems, and software patterns used for implementation and providing solutions for technical problems (software). Particular attention is given to identifying and specifying different business patterns. The main focus is on the activity of design for reuse, i.e. discovery of business patterns and their integration in a pattern catalogue. The first step consisted of a field analysis providing a common terminology and a semantic of the principal concepts managed in PIS and proposing various models to fix these concepts. It forms a basis for exploring the problems frequently occurring during PIS specification. A pattern catalogue is then proposed to solve the identified problems.     

Constant time permutation: an efficient block allocation strategy for variable-bit-rate continuous media data

To provide high accessibility of continuous-media (CM) data, CM servers generally stripe data across multiple disks. Currently, the most widely used striping scheme for CM data is round-robin permutation (RRP). Unfortunately, when RRP is applied to variable-bit-rate (VBR) CM data, load imbalance across multiple disks occurs, thereby reducing overall system performance. In this paper, the performance of a VBR CM server with RRP is analyzed. In addition, we propose an efficient striping scheme called constant time permutation (CTP), which takes the VBR characteristic into account and obtains a more balanced load than RRP. Analytic models of both RRP and CTP are presented, and the models are verified via trace-driven simulations. Analysis and simulation results show that CTP can substantially increase the number of clients supported, though it might introduce a few seconds/minutes of initial delay. Received June 9, 1998 / Accepted January 21, 1999     

Transformation and exchange of multimedia objects in distributed multimedia systems

One of the challenges in the design of a distributed multimedia system is devising suitable specification models for various schemas in different levels of the system. Another important research issue is the integration and synchronization of heterogeneous multimedia objects. In this paper, we present our models for multimedia schemas and transformation algorithms. They transform high-level multimedia objects into schemas that can be used to support the presentation and communication of the multimedia objects. A key module in the system is the Object Exchange Manager (OEM). In this paper, we present the design and implementation of the OEM module, and discuss in detail the interaction between the OEM and other modules in a distributed multimedia system.