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997 research outputs found
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Estimating and Predicting Error Detection Trends and Relative Manpower Utilization
No full textThe work described in this paper outlines an investigative effort focusing on estimating the number of errors remaining in a software product and the effort required to detect those errors. More specifically, we provide a description of a computational model that, through a non-linear optimization process: (a) determines an error detection trend in a given development effort, (b) provides an estimate of the errors remaining in the product and the time required to detect those errors, and (c) relates the error detection effort to current and future manpower requirements. The model is simple to use, requiring only error counts and detection dates as input, and is grounded in the time-tested theory underlying Musa's Basic Reliability Model and the Rayleigh Manpower Utilization Curve. The model has been developed under the auspices of the Software Assurance Technology Center (SATC) at NASA/GSFC. Data sets from various NASA projects were used in formulating and tuning the model. For research purposes, the model was initially developed within an Excel framework; a more robust implementation is currently underway
A Taxonomical Review of Object-Oriented Simulation Model Verification and Validation Techniques
No full textThe goal of this paper is to provide a taxonomical review of verification and validation (V&V) techniques for assessing the accuracy of object-oriented simulation models and to present guidelines for the selection of the techniques based on their effectiveness and costs. The techniques are evaluated based on the identified indicators that relate the techniques to their error detecting capability and the costs that measure the ease-of-use aspects. The paper introduces a preliminary object-oriented model fault taxonomy based on a comprehensive literature survey and authors' experience. The fault taxonomy not only compares and contrasts the error detection capabilities of the techniques but also provides a basis and guidance for detecting specific faults likely to occur due to complexities of object-oriented paradigm such as object/class hierarchies. state-dependent behavior, dynamic and diverse patterns of interactions, among the objects. The guidelines and the comparative analysis of the object-oriented V&V techniques allow practitioners to select the techniques based on the benefits and costs
Adding Value to the Software Development Process: A Study in Independent Verification and Validation
No full textIndependent Verification and Validation (IV&V) is best viewed as an overlay process supporting a software development effort. While the touted benefits of a properly managed IV&V activity are many, they specifically emphasize: (a) early fault detection, (b) reduced time to remove faults, and (c) a more robust end-product. This paper outlines a study funded by NASA-Langley Research Center to examine an existing IV&V methodology, and to confirm (or refute) the touted beneficial claims. In the study two distinct development groups are established, with only one having an IV&V contingent. Both groups are tasked to produce a software product using the same set of requirements. Within each phase of the development effort, fault detection and fault removal data are recorded. An analysis of that data reveals that the group having the IV&V contingent: (a) detected errors earlier in the software development process, and (b) on the average, required significantly less time to remove those faults. Moreover, a test for operational correctness further reveals that the system developed by the group having the IV&V component was substantially more robust than the one produced by the other development group. A statistical analysis of our results is also provided to establish significance
Response Surface Models Combining Linear and Euler Aerodynamics for HSCT Design
No full textA method has been developed to efficiently implement supersonic aerodynamic predictions from Euler solutions into a highly constrained, multidisciplinary design optimization of a High-Speed Civil Transport. The method alleviates the large computational burden associated with performing computational fluid dynamics analyses through the use of variable-complexity modeling techniques, response surface methodologies, and coarse grained parallel computing. Using information gained from lower fidelity aerodynamic models, reduced term response surface models representing a correction to the linear theory response surface model predictions are constructed using Euler solutions. Studies into five, ten, fifteen, and twenty variable design problems show that accurate results can be obtained with the reduced term models at a fraction of the cost of creating the full term quadratic response surface models. Specifically, a savings of 255 CPU hours out of 392 CPU hours required to create the full term response surface model is obtained for the twenty variable problem on a single 75 MHz IP21 processor of a SGI Power Challenge
Derandomized Vector Sorting
No full textAn instance of the vector sorting problem is a sequence of k-dimensional vectors of length n. A solution to the problem is a permutation of the vectors such that in each dimension the length of the longest decreasing subsequence is O(sqrt(n)). A random permutation solves the problem. Here we derandomize the obvious probabilistic algorithm and obtain a deterministic O(kn^3.5) time algorithm that solves the vector sorting problem. We also apply the algorithm to a book embedding problem
Anticipating and Mitigating The Professional Challenge to Independent Verification and Validation
No full textIndependent Verification and Validation faces three classes of challenges: the Technical Challenge, the Management Challenge, and the Professional Challenge. In this paper we focus on the Professional Challenge, and, in particular, the four phases that characterize it: Denial, Anger, Cooperation and Dependence. We believe that to implement an effective IV&V effort, one must understand the relationship among the phases and the critical issues underlying them. For each of the phases we (a) provide a characteristic description, (b) discuss how they affect the IV&V effort, (c) present representative issues and examples, and (d) describe steps to reduce the adverse impact of the three detrimental phases. The examples provided are those we have encountered while serving in an IV&V capacity; "lessons learned" guide our suggestions for addressing phase-specific issues
JavaBeans as a Framework for Collaborative Software
No full textWe describe the use of a popular component framework, JavaBeans, to facilitate developing collaborative software. We describe the class of collaboration-unaware components that can be effectively shared under this framework, and an extension that supports development of efficient collaboration-aware components
WBCSim: A Prototype Problem Solving Environment for Wood-Based Composites Simulations
No full textThis paper describes a computing environment named WBCSim that is intended to increase the productivity of wood scientists conducting research on wood-based composite materials. WBCSim integrates Fortran 77-based simulation codes with a graphical front end, an optimization tool, and a visualization tool. WBCSim serves as a prototype for the design, construction, and evaluation of larger scale problem solving (computing) environments. Several different wood-based composite material simulations are supported. A detailed description of the prototype's software architecture and a typical scenario of use are presented. The system converts output from the simulations to the Virtual Reality Modeling Language (VRML) for visualizing simulation results
A Fortran 90 Genetic Algorithm Module for Composite Laminate Structure Design
No full textThe design of the stacking sequence for a composite laminate involves a set of discrete variables (ply material and ply orientation), and is thus well-suited to genetic algorithms for design optimization. Such algorithms have typically been custom-designed in FORTRAN 77 to suit specific optimization problems. Fortran 90 is a modern, powerful language with features that support important programming concepts, including those used in object-oriented programming. The Fortran 90 genetic algorithm module is used to define genetic data types, the functions which use these data types, and to provide a general framework for solving composite laminate structure design problems. The language's support of abstract data types is used to build genetic structures such as populations, subpopulaions, individuals, chromosomes, and genes, and these data types are combined and manipulated by module subroutines. The use of abstract data types and long variable names makes the code useful and easily understood, while dynamic memory allocation makes the module flexible enough to be used in design problems of varying size and specification
Web Response Time and Proxy Caching
No full textIt is critical to understand WWW latency in order to design better HTTP protocols. In this paper we characterize Web response time and examine effects of proxy caching on response time. We show that at least a quarter of the total elapsed time is spent in setting up TCP connections. We also characterize the effect of a user's network bandwidth on response time. Average connection time from a client via a 33.6 K modem is two times longer than that from a client via switched Ethernet. Contrary to the typical thought about Web proxy caching, this study finds that a single stand alone proxy cache does not always reduce response time. Implications of these results to the HTTP-NG protocol and Web application design also are discussed in the paper