Towards an understanding of the causes and effects of software requirements change: two case studies

Changes to software requirements not only pose a risk to the successful delivery of software applications but also provide opportunity for improved usability and value. Increased understanding of the causes and consequences of change can support requirements management and also make progress towards the goal of change anticipation. This paper presents the results of two case studies that address objectives arising from that ultimate goal. The first case study evaluated the potential of a change source taxonomy containing the elements ‘market’, ‘organisation’, ‘vision’, ‘specification’, and ‘solution’ to provide a meaningful basis for change classification and measurement. The second case study investigated whether the requirements attributes of novelty, complexity, and dependency correlated with requirements volatility. While insufficiency of data in the first case study precluded an investigation of changes arising due to the change source of ‘market’, for the remainder of the change sources, results indicate a significant difference in cost, value to the customer and management considerations. Findings show that higher cost and value changes arose more often from ‘organisation’ and ‘vision’ sources; these changes also generally involved the co-operation of more stakeholder groups and were considered to be less controllable than changes arising from the ‘specification’ or ‘solution’ sources. Results from the second case study indicate that only ‘requirements dependency’ is consistently correlated with volatility and that changes coming from each change source affect different groups of requirements. We conclude that the taxonomy can provide a meaningful means of change classification, but that a single requirement attribute is insufficient for change prediction. A theoretical causal account of requirements change is drawn from the implications of the combined results of the two case studies.

Computational learning of the conditional phase-type (C-Ph) distribution: Learning C-Ph distributions

This paper presents a new algorithm for learning the structure of a special type of Bayesian network. The conditional phase-type (C-Ph) distribution is a Bayesian network that models the probabilistic causal relationships between a skewed continuous variable, modelled by the Coxian phase-type distribution, a special type of Markov model, and a set of interacting discrete variables. The algorithm takes a dataset as input and produces the structure, parameters and graphical representations of the fit of the C-Ph distribution as output.The algorithm, which uses a greedy-search technique and has been implemented in MATLAB, is evaluated using a simulated data set consisting of 20,000 cases. The results show that the original C-Ph distribution is recaptured and the fit of the network to the data is discussed.

Tracking Human Position and Lower Body Parts Using Kalman and Particle Filters Constrained by Human Biomechanics

In this paper, a novel framework for visual tracking of human body parts is introduced. The approach presented demonstrates the feasibility of recovering human poses with data from a single uncalibrated camera by using a limb-tracking system based on a 2-D articulated model and a double-tracking strategy. Its key contribution is that the 2-D model is only constrained by biomechanical knowledge about human bipedal motion, instead of relying on constraints that are linked to a specific activity or camera view. These characteristics make our approach suitable for real visual surveillance applications. Experiments on a set of indoor and outdoor sequences demonstrate the effectiveness of our method on tracking human lower body parts. Moreover, a detail comparison with current tracking methods is presented.

Electron-impact excitation of Fe II

We report in this paper the computation of accurate total collision strengths and effective collision strengths for electron-impact excitation of FeII, using the parallel R-matrix program PRMAT. Target states corresponding to the 3d(6)4s, 3d(7), 3d(6)4p and 3d(5)4s4s basis configurations were included in the calculations giving rise to a 113 LS state 354 coupled channel problem. Following a detailed systematic study of correlation effects in both the target state and collision wavefunctions, it was found that an additional 21 configuration functions needed to be included in the Configuration Interaction expansion to obtain significantly more accurate target states and collision wavefunctions. This much improved 26-configuration model has been used to calculate converged total effective collision strengths for all sextet to quartet transitions among these levels with total spin S=2, giving a total of 1785 lines. These calculations have laid the foundation for an approach which may be adopted in the study of electron collisions with the low ionization stages of other iron peak elements. The work has been further extended with the commencement of a Breit-Pauli relativistic calculation for one of the smaller models and includes 262 fine-structure levels and over 1800 coupled channels. At the same time the PRMAT parallel R-matrix package is being extended to include relativistic effects which will allow us to attempt the more sophisticated 26-configuration model and produce for the first time the amount and quality of atomic data required to perform a meaningful synthesis of the Fe II spectrum.

Chlorostannate(II) Ionic Liquids: Speciation, Lewis Acidity, and Oxidative Stability

The anionic speciation of chlorostannate(II) ionic liquids, prepared by mixing 1-alkyl-3-methylimidazolium chloride and tin(II) chloride in various molar ratios, chi(SnCl2), was investigated in both solid and liquid states. The room temperature ionic liquids were investigated by Sn-119 NMR spectroscopy, X-ray photoelectron spectroscopy, and viscometry. Crystalline samples were studied using Raman spectroscopy, single-crystal X-ray crystallography, and differential scanning calorimetry. Both liquid and solid systems (crystallized from the melt) contained [SnCl3](-) in equilibrium with Cl- when chi(SnCl2) < 0.50, [SnCl3](-) in equilibrium with [Sn2Cl5](-) when chi(SnCl2) > 0.50, and only [SnCl3](-) when chi(SnCl2) = 0.50. Tin(II) chloride was found to precipitate when chi(SnCl2) > 0.63. No evidence was detected for the existence of [SnCl4](-) across the entire range of chi(SnCl2) although such anions have been reported in the literature for chlorostannate(II) organic salts crystallized from organic solvents. Furthermore, the Lewis acidity of the chlorostannate(II)-based systems, expressed by their Gutmann acceptor number, has been determined as a function of the composition, chi(SnCl2), to reveal Lewis acidity for chi(SnCl2) > 0.50 samples comparable to the analogous systems based on zinc(II). A change of the Lewis basicity of the anion was estimated using H-1 NMR spectroscopy, by comparison of the measured chemical shifts of the C-2 hydrogen in the imidazolium ring. Finally, compositions containing free chloride anions (chi(SnCl2) < 0.50) were found to oxidize slowly in air to form a chlorostannate(IV) ionic liquid containing the [SnCl6](2-) anion.

Breast-feeding and childhood-onset type 1 diabetes:A pooled analysis of individual participant data from 43 observational studies

OBJECTIVE: To investigate if there is a reduced risk of type 1 diabetes in children breastfed or exclusively breastfed by performing a pooled analysis with adjustment for recognized confounders.
RESEARCH DESIGN AND METHODS: Relevant studies were identified from literature searches using MEDLINE, Web of Science, and EMBASE. Authors of relevant studies were asked to provide individual participant data or conduct prespecified analyses. Meta-analysis techniques were used to combine odds ratios (ORs) and investigate heterogeneity between studies.
RESULTS: Data were available from 43 studies including 9,874 patients with type 1 diabetes. Overall, there was a reduction in the risk of diabetes after exclusive breast-feeding for >2 weeks (20 studies; OR = 0.75, 95% CI 0.64-0.88), the association after exclusive breast-feeding for >3 months was weaker (30 studies; OR = 0.87, 95% CI 0.75-1.00), and no association was observed after (nonexclusive) breast-feeding for >2 weeks (28 studies; OR = 0.93, 95% CI 0.81-1.07) or >3 months (29 studies; OR = 0.88, 95% CI 0.78-1.00). These associations were all subject to marked heterogeneity (I(2) = 58, 76, 54, and 68%, respectively). In studies with lower risk of bias, the reduced risk after exclusive breast-feeding for >2 weeks remained (12 studies; OR = 0.86, 95% CI 0.75-0.99), and heterogeneity was reduced (I(2) = 0%). Adjustments for potential confounders altered these estimates very little.
CONCLUSIONS: The pooled analysis suggests weak protective associations between exclusive breast-feeding and type 1 diabetes risk. However, these findings are difficult to interpret because of the marked variation in effect and possible biases (particularly recall bias) inherent in the included studies.

Risk-informed decision-making in the presence of epistemic uncertainty

An important issue in risk analysis is the distinction between epistemic and aleatory uncertainties. In this paper, the use of distinct representation formats for aleatory and epistemic uncertainties is advocated, the latter being modelled by sets of possible values. Modern uncertainty theories based on convex sets of probabilities are known to be instrumental for hybrid representations where aleatory and epistemic components of uncertainty remain distinct. Simple uncertainty representation techniques based on fuzzy intervals and p-boxes are used in practice. This paper outlines a risk analysis methodology from elicitation of knowledge about parameters to decision. It proposes an elicitation methodology where the chosen representation format depends on the nature and the amount of available information. Uncertainty propagation methods then blend Monte Carlo simulation and interval analysis techniques. Nevertheless, results provided by these techniques, often in terms of probability intervals, may be too complex to interpret for a decision-maker and we, therefore, propose to compute a unique indicator of the likelihood of risk, called confidence index. It explicitly accounts for the decisionmaker’s attitude in the face of ambiguity. This step takes place at the end of the risk analysis process, when no further collection of evidence is possible that might reduce the ambiguity due to epistemic uncertainty. This last feature stands in contrast with the Bayesian methodology, where epistemic uncertainties on input parameters are modelled by single subjective probabilities at the beginning of the risk analysis process.

From bit level systolic arrays to HDTV processor chips

The initial part of this paper reviews the early challenges (c 1980) in achieving real-time silicon implementations of DSP computations. In particular, it discusses research on application specific architectures, including bit level systolic circuits that led to important advances in achieving the DSP performance levels then required. These were many orders of magnitude greater than those achievable using programmable (including early DSP) processors, and were demonstrated through the design of commercial digital correlator and digital filter chips. As is discussed, an important challenge was the application of these concepts to recursive computations as occur, for example, in Infinite Impulse Response (IIR) filters. An important breakthrough was to show how fine grained pipelining can be used if arithmetic is performed most significant bit (msb) first. This can be achieved using redundant number systems, including carry-save arithmetic. This research and its practical benefits were again demonstrated through a number of novel IIR filter chip designs which at the time, exhibited performance much greater than previous solutions. The architectural insights gained coupled with the regular nature of many DSP and video processing computations also provided the foundation for new methods for the rapid design and synthesis of complex DSP System-on-Chip (SoC), Intellectual Property (IP) cores. This included the creation of a wide portfolio of commercial SoC video compression cores (MPEG2, MPEG4, H.264) for very high performance applications ranging from cell phones to High Definition TV (HDTV). The work provided the foundation for systematic methodologies, tools and design flows including high-level design optimizations based on "algorithmic engineering" and also led to the creation of the Abhainn tool environment for the design of complex heterogeneous DSP platforms comprising processors and multiple FPGAs. The paper concludes with a discussion of the problems faced by designers in developing complex DSP systems using current SoC technology. © 2007 Springer Science+Business Media, LLC.

Rijndael FPGA implementations utilising look-up tables

This paper presents single-chip FPGA Rijndael algorithm implementations of the Advanced Encryption Standard (AES) algorithm, Rijndael. In particular, the designs utilise look-up tables to implement the entire Rijndael Round function. A comparison is provided between these designs and similar existing implementations. Hardware implementations of encryption algorithms prove much faster than equivalent software implementations and since there is a need to perform encryption on data in real time, speed is very important. In particular, Field Programmable Gate Arrays (FPGAs) are well suited to encryption implementations due to their flexibility and an architecture, which can be exploited to accommodate typical encryption transformations. In this paper, a Look-Up Table (LUT) methodology is introduced where complex and slow operations are replaced by simple LUTs. A LUT-based fully pipelined Rijndael implementation is described which has a pre-placement performance of 12 Gbits/sec, which is a factor 1.2 times faster than an alternative design in which look-up tables are utilised to implement only one of the Round function transformations, and 6 times faster than other previous single-chip implementations. Iterative Rijndael implementations based on the Look-Up-Table design approach are also discussed and prove faster than typical iterative implementations.

Extracting Query Interfaces Based on Form Structures and Semantic Similarity

Web databases are now pervasive. Such a database can be accessed via its query interface (usually HTML query form) only. Extracting Web query interfaces is a critical step in data integration across multiple Web databases, which creates a formal representation of a query form by extracting a set of query conditions in it. This paper presents a novel approach to extracting Web query interfaces. In this approach, a generic set of query condition rules are created to define query conditions that are semantically equivalent to SQL search conditions. Query condition rules represent the semantic roles that labels and form elements play in query conditions, and how they are hierarchically grouped into constructs of query conditions. To group labels and form elements in a query form, we explore both their structural proximity in the hierarchy of structures in the query form, which is captured by a tree of nested tags in the HTML codes of the form, and their semantic similarity, which is captured by various short texts used in labels, form elements and their properties. We have implemented the proposed approach and our experimental results show that the approach is highly effective.

Cannibale, Frigidaire, and the Multitude: Post-1977 Italian Comics through Radical Theory

A direct connection between comics and contemporary critical theory is to be found in the activity of the collective of artists who created "Cannibale" and "Frigidaire", the two most innovative Italian comics magazines of the late 1970s and early 1980s. The work of Andrea Pazienza, Filippo Scòzzari, Stefano Tamburini, Tanino Liberatore and Massimo Mattioli should be regarded as an expression of the radical movements from which Marxist Autonomist thinkers such as Antonio Negri, Franco ‘Bifo’ Berardi and Paolo Virno also emerged in the same period. As a consequence, the writings of the latter can be used to analyse the narrative and visual style, the recurring themes, and the editorial characteristics of the comics of the former. Moreover, an interesting parallel can also be drawn between the work of the most influential of these artists, Andrea Pazienza, and the thought of another prominent Italian philosopher, Giorgio Agamben, whose earliest books were published at that time too. The aim of this article is to show that the ideas of a number of the thinkers who have recently become internationally known as representatives of radical Italian theory, are useful to understand the work of this group of comics authors.