Christopher P. Fuhrman

TreeMatrix: A Hybrid Visualization of Compound Graphs

We present a hybrid visualization technique for compound graphs (i.e. networks with a hierarchical clustering defined on the nodes) that combines the use of adjacency matrices, node‐link and arc diagrams to show the graph, and also combines the use of nested inclusion and icicle diagrams to show the hierarchical clustering. The graph visualized with our technique may have edges that are weighted and/or directed. We first explore the design space of visualizations of compound graphs and present a taxonomy of hybrid visualization techniques. We then present our prototype, which allows clusters (i.e. subtrees) of nodes to be grouped into matrices or split apart using a radial menu. We also demonstrate how our prototype can be used in the software engineering domain, and compare it to the commercial matrix‐based visualization tool Lattix using a qualitative user study.

Establishing a generic and multidimensional measurement repository in CMMI context

We propose a measurement repository for collecting, storing, analyzing and reporting measurement data based on the requirements of the capability maturity model integrated (CMMI). Our repository is generic, flexible and integrated, supporting a dynamic measurement system. It was originally designed to support Ericsson Research Canadas business information needs. Our multidimensional repository can relate measurement information needs to CMMI processes and products requirements. The data model is based on a hierarchical and multidimensional definition of measurement data. It has been developed based on the concept of a data warehouse environment. Reporting features are based on the definition of queries to on line analytical process (OLAP) cubes. OLAP cubes are created as materialized views of the measurement data, and the user functionalities are implemented as analytical drill-down/roll-up capabilities and as indicator and trend analysis capabilities.

A comparative analysis of hardware and software fault tolerance: Impact on software reliability engineering

Todays digital systems are growing increasingly complex, and are being used in increasingly critical functions. The first premise makes them more prone to contain faults, and the second premise makes their failure less tolerable. This widening gap highlights the need for fault tolerant techniques, which make provisions for reliable operation of digital systems despite the presence and occasional manifestation of faults. In this paper we present a brief comparative survey of fault tolerance as it arises in hardware systems and software systems. We discuss logical models as well as statistical models of fault tolerance, and use these models to analyze design tradeoffs of fault tolerant systems.

Hardware/software fault tolerance with multiple task modular redundancy

N-modular redundancy (NMR) and N-version programming (NVP) are two popular fault tolerance techniques in which hardware and software redundancy is exploited to mask faults. Redundant hardware is used to improve fault tolerance rather than throughput. We introduce a scheme for combined hardware-software fault tolerance derived from NMR and NVP that shows how redundancy can also be used to improve throughput by grouping the execution of several tasks. Our scheme uses a dynamic task allocation algorithm with an optimistic execution policy where the number of task executions is kept close to the minimum required to produce fault-free results. For equivalent hardware and software resources, the proposed method is 50% to 100% more efficient in terms of throughput and latency.

Change Propagation for Assessing Design Quality of Software Architectures

The study of software architectures is gaining importance due to its role in various aspects of software engineering such as product line engineering, component based software engineering and other emerging paradigms. With the increasing emphasis on design patterns, the traditional practice of ad-hoc software construction is slowly shifting towards pattern-oriented development. Various architectural attributes like error propagation, change propagation, and requirements propagation, provide a wealth of information about software architectures. In this paper, we show that change propagation probability (CP) is helpful and effective in assessing the design quality of software architectures. We study two different architectures (one that employs patterns versus one that does not) for the same application. We also analyze and compare change propagation metric with respect to other coupling-based metrics.

Towards defining software development processes in DO-178B with openup

Civil avionics software must be certified according to standards mandated by governmental agencies, such as the Federal Aviations Administration in the United States. Typically the certification is done in the context of the DO-178B standard. For companies seeking a first-time certification, preparation for DO-178B can be a daunting challenge. The documentation and planning of high-integrity software is therefore a software engineering problem. As a solution, we consider an open-source derivative of the Unified Process, called OpenUP, as a base process model from which to begin. Because of their importance in the DO-178B standard, software requirement activities are the focus of our study. We show that most of DO-178Bpsilas objectives in this dimension could be supported with activities in OpenUP.

Lightweight models for interpreting informal specifications

We explore the use of lightweight models, namely those in PROMELA/SPIN, by software engineers within the life cycle of software development. The primary goal is to improve the interpretation and understanding of an informal specification, not necessarily to validate the specification. We give details of an example involving an informal specification of an application protocol in telecommunications, namely the Request for Comments (RFC) standard for the Trivial File Transfer protocol (TFTP). We show how we were able to use this type of modelling in an iterative process, using tools that facilitate the process.

Fault Tolerance with Multiple Task Modular Redundancy

Abstract The redundant units in a classic N Modular Redundancy (NMR) system are employed solely for fault tolerance, making this technique inefficient. This paper introduces Multiple Task Modular Redundancy that allows an NMR system to have a higher throughput by exploiting, when no faults have occurred, the system’s redundancy. More than one group of replicated tasks are optimistically executed. This method has a 50-100% better throughput over NMR but does not jeopardize the fault tolerance of the basic NMR system. Unlike other methods, this technique applies to systems as small as three processors (TMR). Variations on the granularity and dependencies of tasks are considered.

Using Change Propagation Probabilities to Assess Quality Attributes of Software Architectures 1

The study of software architectures is gaining importance due to its role in various aspects of software engineering, like product line engineering, componentbased software engineering and other emerging paradigms. With the increasing emphasis on design patterns, the traditional practice of ad-hoc software construction is slowly shifting towards pattern-oriented development. Various architectural attributes like error propagation, change propagation, requirements propagation provide a wealth of information about software architectures. In this paper, we show that change propagation probability (CP) is helpful and effective in assessing the design quality of software architectures. We study two different architectures (one that employs patterns versus one that does not) for the same application. We also analyze and compare the change propagation metric with respect to other coupling-based metrics.

Comparison diagnosis in large multiprocessor systems

We present the bounded symmetric comparison (BSC) model for comparison-based system-level diagnosis. It is based on the symmetric comparison model of Chwa and Hakimi but includes a limit on the number of PEs that can produce identical, faulty results that are used in the syndrome of the diagnosis. We contribute a theorem with necessary and sufficient conditions for one-step diagnosability of a system under the BSC model. We show that previous characterizations for one-step diagnosability under the symmetric (Chwa/Hakimi) and asymmetric (Malek) comparison models are in fact special-case characterizations for the BSC model.