Paolo Tonella

Analysis and testing of Web applications

The economic relevance of Web applications increases the importance of controlling and improving their quality. Moreover, the newly available technologies for their development allow the insertion of sophisticated functions, but often leave the developers responsible for their organization and evolution. As a consequence, a high demand is emerging for methodologies and tools for the quality assurance of Web-based systems. In this paper, a UML model of Web applications is proposed for their high-level representation. Such a model is the starting point for several analyses, which can help in the assessment of the static site structure. Moreover, it drives Web application testing, in that it can be exploited to define white-box testing criteria and to semi-automatically generate the associated test cases. The proposed techniques were applied to several real-world Web applications. The results suggest that automatic support for verification and validation activities can be extremely beneficial. In fact, it guarantees that all paths in the site which satisfy a selected criterion are properly exercised before delivery. The high level of automation that is achieved in test case generation and execution increases the number of tests that are conducted and simplifies the regression checks.

Evolutionary testing of classes

Object oriented programming promotes reuse of classes in multiple contexts. Thus, a class is designed and implemented with several usage scenarios in mind, some of which possibly open and generic. Correspondingly, the unit testing of classes cannot make too strict assumptions on the actual method invocation sequences, since these vary from application to application.In this paper, a genetic algorithm is exploited to automatically produce test cases for the unit testing of classes in a generic usage scenario. Test cases are described by chromosomes, which include information on which objects to create, which methods to invoke and which values to use as inputs. The proposed algorithm mutates them with the aim of maximizing a given coverage measure. The implementation of the algorithm and its application to classes from the Java standard library are described.

State-Based Testing of Ajax Web Applications

Ajax supports the development of rich-client Web applications, by providing primitives for the execution of asynchronous requests and for the dynamic update of the page structure and content. Often, Ajax Web applications consist of a single page whose elements are updated in response to callbacks activated asynchronously by the user or by a server message. These features give rise to new kinds of faults that are hardly revealed by existing Web testing approaches. In this paper, we propose a novel state-based testing approach, specifically designed to exercise Ajax Web applications. The document object model (DOM) of the page manipulated by the Ajax code is abstracted into a state model. Callback executions triggered by asynchronous messages received from the Web server are associated with state transitions. Test cases are derived from the state model based on the notion of semantically interacting events. We evaluate the approach on a case study in terms of fault revealing capability. We also measure the amount of manual interventions involved in constructing and refining the model required by this approach.

Aspect mining through the formal concept analysis of execution traces

The presence of crosscutting concerns, i.e., functionalities that are not assigned to a single modular unit in the implementation, is one of the major problems in software understanding and evolution. In fact, they are hard to locate (scattering) and may give rise to multiple ripple effects (tangling). Aspect oriented programming offers mechanisms to factor them out into a modular unit, called an aspect. Aspect identification in existing code is supported by means of dynamic code analysis. Execution traces are generated for the use cases that exercise the main functionalities of the given application. The relationship between execution traces and executed computational units (class methods) is subjected to concept analysis. In the resulting lattice, potential aspects are detected by determining the use-case specific concepts and examining their specific computational units. When these come from multiple modules (classes) which contribute to multiple use-cases, a candidate aspect is recognized.

Using a concept lattice of decomposition slices for program understanding and impact analysis

The decomposition slice graph and concept lattice are two program representations used to abstract the details of code into a higher-level view of the program. The decomposition slice graph partitions the program into computations performed on different variables and shows the dependence relation between computations, holding when a computation needs another computation as a building block. The concept lattice groups program entities which share common attributes and organizes such groupings into a hierarchy of concepts, which are related through generalizations/specializations. This paper investigates the relationship existing between these two program representations. The main result of this paper is a novel program representation, called concept lattice of decomposition slices, which is shown to be an extension of the decomposition slice graph, and is obtained by means of concept analysis, with additional nodes associated with weak interferences between computations, i.e., shared statements which are not decomposition slices. The concept lattice of decomposition slices can be used to support software maintenance by providing relevant information about the computations performed by a program and the related dependences/interferences, as well as by representing a natural data structure on which to conduct impact analysis. Preliminary results on small to medium size code support the applicability of this method at the intraprocedural level or when investigating the dependences among small groups of procedures.

EEG data compression techniques

Electroencephalograph (EEG) and Holter EEG data compression techniques which allow perfect reconstruction of the recorded waveform from the compressed one are presented and discussed. Data compression permits one to achieve significant reduction in the space required to store signals and in transmission time. The Huffman coding technique in conjunction with derivative computation reaches high compression ratios (on average 49% on Holter and 58% on EEG signals) with low computational complexity. By exploiting this result a simple and fast encoder/decoder scheme capable of real-time performance on a PC was implemented. This simple technique is compared with other predictive transformations, vector quantization, discrete cosine transform (DCT), and repetition count compression methods. Finally, it is shown that the adoption of a collapsed Huffman tree for the encoding/decoding operations allows one to choose the maximum codeword length without significantly affecting the compression ratio. Therefore, low cost commercial microcontrollers and storage devices can be effectively used to store long Holter EEGs in a compressed format.

Concept analysis for module restructuring

Low coupling between modules and high cohesion inside each module are the key features of good software design. This paper proposes a new approach to using concept analysis for module restructuring, based on the computation of extended concept subpartitions. Alternative modularizations, characterized by high cohesion around the internal structures that are being manipulated, can be determined by such a method. To assess the quality of the restructured modules, the trade-off between encapsulation violations and decomposition is considered, and proper measures for both factors are defined. Furthermore, the cost of restructuring is evaluated through a measure of distance between the original and the new modularizations. Concept subpartitions were determined for a test suite of 20 programs of variable size: 10 public-domain and 10 industrial applications. The trade-off between encapsulation and decomposition was measured on the resulting module candidates, together with an estimate of the cost of restructuring. Moreover, the ability of concept analysis to determine meaningful modularizations was assessed in two ways. First, programs without encapsulation violations were used as oracles, assuming the absence of violations as an indicator of careful decomposition. Second, the suggested restructuring interventions were actually implemented in some case studies to evaluate the feasibility of restructuring and to deeply investigate the code organization before and after the intervention. Concept analysis was experienced to be a powerful tool supporting module restructuring.

Clustering test cases to achieve effective and scalable prioritisation incorporating expert knowledge

Pair-wise comparison has been successfully utilised in order to prioritise test cases by exploiting the rich, valuable and unique knowledge of the tester. However, the prohibitively large cost of the pair-wise comparison method prevents it from being applied to large test suites. In this paper, we introduce a cluster-based test case prioritisation technique. By clustering test cases, based on their dynamic runtime behaviour, we can reduce the required number of pair-wise comparisons significantly. The approach is evaluated on seven test suites ranging in size from 154 to 1,061 test cases. We present an empirical study that shows that the resulting prioritisation is more effective than existing coverage-based prioritisation techniques in terms of rate of fault detection. Perhaps surprisingly, the paper also demonstrates that clustering (even without human input) can outperform unclustered coverage-based technologies, and discusses an automated process that can be used to determine whether the application of the proposed approach would yield improvement.

Understanding and restructuring Web sites with ReWeb

The authors investigated automatic and semiautomatic Web site analysis with our tool ReWeb, focusing on a sites architecture and evolution. A case study demonstrates how ReWeb addresses the need to support Web site maintenance and evolution while retaining and possibly improving quality. Although not definitive, the case study described confirms that an automatic or semiautomatic tool can help developers understand and maintain Web sites. High-level views, describing the overall site architecture, are very useful, and detailed analyses can help with a sites enclosed subparts. Specifically, we based restructuring on the reaching frames, dominators, and shortest path analyses. In fact, they highlight structural and navigation problems before restructuring and their absence after the intervention. We devote future work to improving the ReWebs robustness, widening the spectrum of analyzable sites, and enriching its set of analyses and facilities. We would also like to add abstraction techniques to support a high-level view of the site and to partially automate input selection in the presence of dynamic pages.

Object oriented design pattern inference

When designing a new application, experienced software engineers usually try to employ solutions that proved successful in previous projects. Such reuse of code organizations is seldom made explicit. Nevertheless it represents important information about the system, that can be extremely valuable in the maintenance phase by documenting the design choices underlying the implementation. In addition, having it available, it can be reused whenever a similar problem is encountered. In this paper an approach is proposed to the inference of recurrent design patterns directly from the code or the design. No assumption is made on the availability of any pattern library and the concept analysis algorithm, adapted for this purpose, is able to infer the presence of class groups which instantiate a common, repeated pattern. In fact, concept analysis provides sets of objects sharing attributes, which, in the case of object oriented design patterns, become class members or inter-class relations. The approach was applied to a C++ application, for which the structural relations among classes led to the extraction of a set of structural design patterns, which could be enriched with non structural information about class members and method invocations. The resulting patterns could be interpreted as meaningful organizations aimed at solving general problems which have several instances in the analyzed application.