Predicting fault-prone software modules in telephone switches

An empirical study was carried out at Ericsson Telecom AB to investigate the relationship between several design metrics and the number of function test failure reports associated with software modules. A tool, ERIMET, was developed to analyze the design documents automatically. Preliminary results from the study of 130 modules showed that: based on fault and design data one can satisfactorily build, before coding has started, a prediction model for identifying the most fault-prone modules. The data analyzed show that 20 percent of the most fault-prone modules account for 60 percent of all faults. The prediction model built in this paper would have identified 20 percent of the modules accounting for 47 percent of all faults. At least four design measures can alternatively be used as predictors with equivalent performance. The size (with respect to the number of lines of code) used in a previous prediction model was not significantly better than these four measures. The Alberg diagram introduced in this paper offers a way of assessing a predictor based on historical data, which is a valuable complement to linear regression when prediction data is ordinal. Applying the method described in this paper makes it possible to use measures at the design phase to predict the most fault-prone modules     

A Replicated Quantitative Analysis of Fault Distributions in Complex Software Systems

To contribute to the body of empirical research on fault distributions during development of complex software systems, a replication of a study of Fenton and Ohlsson is conducted. The hypotheses from the original study are investigated using data taken from an environment that differs in terms of system size, project duration, and programming language. We have investigated four sets of hypotheses on data from three successive telecommunications projects: 1) the Pareto principle, that is, a small number of modules contain a majority of the faults (in the replication, the Pareto principle is confirmed), 2) fault persistence between test phases (a high fault incidence in function testing is shown to imply the same in system testing, as well as prerelease versus postrelease fault incidence), 3) the relation between number of faults and lines of code (the size relation from the original study could be neither confirmed nor disproved in the replication), and 4) fault density similarities across test phases and projects (in the replication study, fault densities are confirmed to be similar across projects). Through this replication study, we have contributed to what is known on fault distributions, which seem to be stable across environments.     

Empirical Analysis of Object-Oriented Design Metrics for Predicting High and Low Severity Faults

In the last decade, empirical studies on object-oriented design metrics have shown some of them to be useful for predicting the fault-proneness of classes in object-oriented software systems. This research did not, however, distinguish among faults according to the severity of impact. It would be valuable to know how object-oriented design metrics and class fault-proneness are related when fault severity is taken into account. In this paper, we use logistic regression and machine learning methods to empirically investigate the usefulness of object-oriented design metrics, specifically, a subset of the Chidamber and Kemerer suite, in predicting fault-proneness when taking fault severity into account. Our results, based on a public domain NASA data set, indicate that 1) most of these design metrics are statistically related to fault-proneness of classes across fault severity, and 2) the prediction capabilities of the investigated metrics greatly depend on the severity of faults. More specifically, these design metrics are able to predict low severity faults in fault-prone classes better than high severity faults in fault-prone classes     

Analogy-Based Practical Classification Rules for Software Quality Estimation

Software metrics-based quality estimation models can be effective tools for identifying which modules are likely to be fault-prone or not fault-prone. The use of such models prior to system deployment can considerably reduce the likelihood of faults discovered during operations, hence improving system reliability. A software quality classification model is calibrated using metrics from a past release or similar project, and is then applied to modules currently under development. Subsequently, a timely prediction of which modules are likely to have faults can be obtained. However, software quality classification models used in practice may not provide a useful balance between the two misclassification rates, especially when there are very few faulty modules in the system being modeled.This paper presents, in the context of case-based reasoning, two practical classification rules that allow appropriate emphasis on each type of misclassification as per the project requirements. The suggested techniques are especially useful for high-assurance systems where faulty modules are rare. The proposed generalized classification methods emphasize on the costs of misclassifications, and the unbalanced distribution of the faulty program modules. We illustrate the proposed techniques with a case study that consists of software measurements and fault data collected over multiple releases of a large-scale legacy telecommunication system. In addition to investigating the two classification methods, a brief relative comparison of the techniques is also presented. It is indicated that the level of classification accuracy and model-robustness observed for the case study would be beneficial in achieving high software reliability of its subsequent system releases. Similar observations are made from our empirical studies with other case studies.     

Application of multivariate analysis for software fault prediction

Prediction of fault-prone modules provides one way to support software quality engineering through improved scheduling and project control. The primary goal of our research was to develop and refine techniques for early prediction of fault-prone modules. The objective of this paper is to review and improve an approach previously examined in the literature for building prediction models, i.e. principal component analysis (PCA) and discriminant analysis (DA). We present findings of an empirical study at Ericsson Telecom AB for which the previous approach was found inadequate for predicting the most fault-prone modules using software design metrics. Instead of dividing modules into fault-prone and not-fault-prone, modules are categorized into several groups according to the ordered number of faults. It is shown that the first discriminant coordinates (DC) statistically increase with the ordering of modules, thus improving prediction and prioritization efforts. The authors also experienced problems with the smoothing parameter as used previously for DA. To correct this problem and further improve predictability, separate estimation of the smoothing parameter is shown to be required.     

An effective fault prediction model developed using an extreme learning machine with various kernel methods

System analysts often use software fault prediction models to identify fault-prone modules during the design phase of the software development life cycle. The models help predict faulty modules based on the software metrics that are input to the models. In this study, we consider 20 types of metrics to develop a model using an extreme learning machine associated with various kernel methods. We evaluate the effectiveness of the mode using a proposed framework based on the cost and efficiency in the testing phases. The evaluation process is carried out by considering case studies for 30 object-oriented software systems. Experimental results demonstrate that the application of a fault prediction model is suitable for projects with the percentage of faulty classes below a certain threshold, which depends on the efficiency of fault identification (low: 47.28%; median: 39.24%; high: 25.72%). We consider nine feature selection techniques to remove the irrelevant metrics and to select the best set of source code metrics for fault prediction.     

Empirical validation of object-oriented metrics for predicting fault proneness models

Empirical validation of software metrics used to predict software quality attributes is important to ensure their practical relevance in software organizations. The aim of this work is to find the relation of object-oriented (OO) metrics with fault proneness at different severity levels of faults. For this purpose, different prediction models have been developed using regression and machine learning methods. We evaluate and compare the performance of these methods to find which method performs better at different severity levels of faults and empirically validate OO metrics given by Chidamber and Kemerer. The results of the empirical study are based on public domain NASA data set. The performance of the predicted models was evaluated using Receiver Operating Characteristic (ROC) analysis. The results show that the area under the curve (measured from the ROC analysis) of models predicted using high severity faults is low as compared with the area under the curve of the model predicted with respect to medium and low severity faults. However, the number of faults in the classes correctly classified by predicted models with respect to high severity faults is not low. This study also shows that the performance of machine learning methods is better than logistic regression method with respect to all the severities of faults. Based on the results, it is reasonable to claim that models targeted at different severity levels of faults could help for planning and executing testing by focusing resources on fault-prone parts of the design and code that are likely to cause serious failures.     

Uncertain Classification of Fault-Prone Software Modules

Many development organizations try to minimize faults in software as a means for improving customer satisfaction. Assuring high software quality often entails time-consuming and costly development processes. A software quality model based on software metrics can be used to guide enhancement efforts by predicting which modules are fault-prone. This paper presents statistical techniques to determine which predictions by a classification tree should be considered uncertain. We conducted a case study of a large legacy telecommunications system. One release was the basis for the training dataset, and the subsequent release was the basis for the evaluation dataset. We built a classification tree using the TREEDISC algorithm, which is based on ² tests of contingency tables. The model predicted whether a module was likely to have faults discovered by customers, or not, based on software product, process, and execution metrics. We simulated practical use of the model by classifying the modules in the evaluation dataset. The model achieved useful accuracy, in spite of the very small proportion of fault-prone modules in the system. We assessed whether the classes assigned to the leaves were appropriate by statistical tests, and found sizable subsets of modules with uncertain classification. Discovering which modules have uncertain classifications allows sophisticated enhancement strategies to resolve uncertainties. Moreover, TREEDISC is especially well suited to identifying uncertain classifications.     

Semantic metrics for software testability

Software faults that infrequently affect output cause problems in most software and are dangerous in safety-critical systems. When a software fault causes frequent software failures, testing is likely to reveal the fault before the software is released; when the fault “hides” from testing, the hidden fault can cause disaster after the software is installed. During the design of safety-critical software, we can isolate certain subfunctions of the software that tend to hide faults. A simple metric, derivable from semantic information found in software specifications, indicates software subfunctions that tend to hide faults. The metric is the domain/range ratio (DRR): the ratio of the cardinality of the possible inputs to the cardinality of the possible outputs. By isolating modules that implement a high DRR function during design, we can produce programs that are less likely to hide faults during testing. The DRR is available early in the software lifecycle; when code has been produced, the potential for hidden faults can be further explored using empirical methods. Using the DRR during design and empirical methods during execution, we can better plan and implement strategies for enhancing testability. For certain specifications, testability considerations can help produce modules that require less additional testing when assumptions change about the distribution of inputs. Such modules are good candidates for software reuse.     

Estimating software readiness using predictive models

In this study, defect tracking is used as a proxy method to predict software readiness. The number of remaining defects in an application under development is one of the most important factors that allow one to decide if a piece of software is ready to be released. By comparing predicted number of faults and number of faults discovered in testing, software manager can decide whether the software is likely ready to be released or not.The predictive model developed in this research can predict: (i) the number of faults (defects) likely to exist, (ii) the estimated number of code changes required to correct a fault and (iii) the estimated amount of time (in minutes) needed to make the changes in respective classes of the application. The model uses product metrics as independent variables to do predictions. These metrics are selected depending on the nature of source code with regards to architecture layers, types of faults and contribution factors of these metrics. The use of neural network model with genetic training strategy is introduced to improve prediction results for estimating software readiness in this study. This genetic-net combines a genetic algorithm with a statistical estimator to produce a model which also shows the usefulness of inputs.The model is divided into three parts: (1) prediction model for presentation logic tier (2) prediction model for business tier and (3) prediction model for data access tier. Existing object-oriented metrics and complexity software metrics are used in the business tier prediction model. New sets of metrics have been proposed for the presentation logic tier and data access tier. These metrics are validated using data extracted from real world applications. The trained models can be used as tools to assist software mangers in making software release decisions.     

Predicting fault incidence using software change history

This paper is an attempt to understand the processes by which software ages. We define code to be aged or decayed if its structure makes it unnecessarily difficult to understand or change and we measure the extent of decay by counting the number of faults in code in a period of time. Using change management data from a very large, long-lived software system, we explore the extent to which measurements from the change history are successful in predicting the distribution over modules of these incidences of faults. In general, process measures based on the change history are more useful in predicting fault rates than product metrics of the code: For instance, the number of times code has been changed is a better indication of how many faults it will contain than is its length. We also compare the fault rates of code of various ages, finding that if a module is, on the average, a year older than an otherwise similar module, the older module will have roughly a third fewer faults. Our most successful model measures the fault potential of a module as the sum of contributions from all of the times the module has been changed, with large, recent changes receiving the most weight     

Empirical analysis of network measures for predicting high severity software faults

Network measures are useful for predicting fault-prone modules. However, existing work has not distinguished faults according to their severity. In practice, high severity faults cause serious problems and require further attention. In this study, we explored the utility of network measures in high severity faultproneness prediction. We constructed software source code networks for four open-source projects by extracting the dependencies between modules. We then used univariate logistic regression to investigate the associations between each network measure and fault-proneness at a high severity level. We built multivariate prediction models to examine their explanatory ability for fault-proneness, as well as evaluated their predictive effectiveness compared to code metrics under forward-release and cross-project predictions. The results revealed the following: (1) most network measures are significantly related to high severity fault-proneness; (2) network measures generally have comparable explanatory abilities and predictive powers to those of code metrics; and (3) network measures are very unstable for cross-project predictions. These results indicate that network measures are of practical value in high severity fault-proneness prediction.     

Deriving a Fault Architecture to Guide Testing

Defect analysis of software components can be used to guide testing, with the goal of focusing on parts of the software that were fault-prone in earlier releases or earlier life cycle phases, such as development. We replicate a study that adapted a reverse architecting technique using defect reports to derive fault architectures. A fault architecture determines and visualizes components that are fault-prone in their relationships with other components, as well as those that are locally fault-prone. Our case study uses defect data from three releases of a large medical record system to identify relationships among system components, based on whether they are involved in the same defect report.We investigate measures that assess the fault-proneness of components and component relationships. Component relationships are used to derive a fault architecture. The resulting fault architecture indicates what the most fault-prone relationships are in a release. We also apply the technique in a new way. Not only do we derive fault architectures for each release, we derive fault architectures for the development, system test and post release phases within each release. Comparing across releases, makes it possible to see whether some components are repeatedly in fault-prone relationships. Comparing across phases, makes it possible to see whether development fault architectures can be used to identify those parts of the software that need to be tested more. We validate our predictions using system test data from the same release. We also use the development and system test fault architectures to identify fault-prone components after release, and validate our predictions using post release data.     

Ordering Fault-Prone Software Modules

Software developers apply various techniques early in development to improve software reliability, such as extra reviews, additional testing, and strategic assignment of personnel. Due to limited resources and time, it is often not practical to enhance the reliability of all modules. Our goal is to target reliability enhancement activities to those modules that would otherwise have problems later. Prior research has shown that a software quality model based on software product and process metrics can predict which modules are likely to have faults.A module-order model is a quantitative software quality model that is used to predict the rank-order of modules according to a quality factor, such as the number of faults. The contribution of this paper is definition of module-order models and a method for their evaluation and use. Two empirical case studies of full-scale industrial software systems provide empirical evidence of the usefulness of module-order models for targeting reliability enhancement.     

Towards an ensemble based system for predicting the number of software faults

Software fault prediction using different techniques has been done by various researchers previously. It is observed that the performance of these techniques varied from dataset to dataset, which make them inconsistent for fault prediction in the unknown software project. On the other hand, use of ensemble method for software fault prediction can be very effective, as it takes the advantage of different techniques for the given dataset to come up with better prediction results compared to individual technique. Many works are available on binary class software fault prediction (faulty or non-faulty prediction) using ensemble methods, but the use of ensemble methods for the prediction of number of faults has not been explored so far. The objective of this work is to present a system using the ensemble of various learning techniques for predicting the number of faults in given software modules. We present a heterogeneous ensemble method for the prediction of number of faults and use a linear combination rule and a non-linear combination rule based approaches for the ensemble. The study is designed and conducted for different software fault datasets accumulated from the publicly available data repositories. The results indicate that the presented system predicted number of faults with higher accuracy. The results are consistent across all the datasets. We also use prediction at level l (Pred(l)), and measure of completeness to evaluate the results. Pred(l) shows the number of modules in a dataset for which average relative error value is less than or equal to a threshold value l. The results of prediction at level l analysis and measure of completeness analysis have also confirmed the effectiveness of the presented system for the prediction of number of faults. Compared to the single fault prediction technique, ensemble methods produced improved performance for the prediction of number of software faults. Main impact of this work is to allow better utilization of testing resources helping in early and quick identification of most of the faults in the software system.     

Fault Prediction Modeling for Software Quality Estimation: Comparing Commonly Used Techniques

High-assurance and complex mission-critical software systems are heavily dependent on reliability of their underlying software applications. An early software fault prediction is a proven technique in achieving high software reliability. Prediction models based on software metrics can predict number of faults in software modules. Timely predictions of such models can be used to direct cost-effective quality enhancement efforts to modules that are likely to have a high number of faults. We evaluate the predictive performance of six commonly used fault prediction techniques: CART-LS (least squares), CART-LAD (least absolute deviation), S-PLUS, multiple linear regression, artificial neural networks, and case-based reasoning. The case study consists of software metrics collected over four releases of a very large telecommunications system. Performance metrics, average absolute and average relative errors, are utilized to gauge the accuracy of different prediction models. Models were built using both, original software metrics (RAW) and their principle components (PCA). Two-way ANOVA randomized-complete block design models with two blocking variables are designed with average absolute and average relative errors as response variables. System release and the model type (RAW or PCA) form the blocking variables and the prediction technique is treated as a factor. Using multiple-pairwise comparisons, the performance order of prediction models is determined. We observe that for both average absolute and average relative errors, the CART-LAD model performs the best while the S-PLUS model is ranked sixth.     

遗传优化支持向量机的软件可靠性预测模型

软件可靠性预测在软件开发的早期就能预测出哪些模块有出错倾向。提出一种改进的支持向量机来进行软件可靠性预测。针对支持向量机参数难选择的问题,将遗传算法引入到支持向量机的参数选择中,构造基于遗传算法优化支持向量机的软件可靠性预测模型,并用主成分分析的方法对软件度量数据进行降维,通过仿真实验,证明该模型比支持向量机、BP神经网络、分类回归树和聚类分析等预测模型具有更高的预测精度。     

A Comparative Study of Ordering and Classification of Fault-Prone Software Modules

Software quality models can predict the quality of modules early enough for cost-effective prevention of problems. For example, software product and process metrics can be the basis for predicting reliability. Predicting the exact number of faults is often not necessary; classification models can identify fault-prone modules. However, such models require that fault-prone be defined before modeling, usually via a threshold. This may not be practical due to uncertain limits on the amount of reliability-improvement effort. In such cases, predicting the rank-order of modules is more useful.A module-order model predicts the rank-order of modules according to a quantitative quality factor, such as the number of faults. This paper demonstrates how module-order models can be used for classification, and compares them with statistical classification models.Two case studies of full-scale industrial software systems compared nonparametric discriminant analysis with module-order models. One case study examined a military command, control, and communications system. The other studied a large legacy telecommunications system. We found that module-order models give management more flexible reliability enhancement strategies than classification models, and in these case studies, yielded more accurate results than corresponding discriminant models.     

Application of neural networks for predicting program faults

Accurately predicting the number of faults in program modules is a major problem in the quality control of large software development efforts. Some software complexity metrics are closely related to the distribution of faults across program modules. Using these relationships, software engineers develop models that provide early estimates of quality metrics that do not become available until late in the development cycle. By considering these early estimates, software engineers can take actions to avoid or prepare for emerging quality problems. Most often, the predictive models are based upon multiple regression analysis. However, measures of software quality and complexity exhibit systematic departures from the assumptions of these analyses. With extreme violations of these assumptions, multiple regression models become unstable and lose most of their predictive quality. Since neural network models carry no data assumptions, these models could be more appropriate than regression models for modeling software faults. In this paper, we explore a neural network methodology for developing models that predict the number of faults in program modules. We apply this methodology to develop neural network models based upon data collected during the development of two commercial software systems. After developing neural network models, we apply multiple linear regression methods to develop regression models on the same data. For the data sets considered, the neural network methodology produced better predictive models in terms of both quality of fit and predictive quality.