The first goal of this paper is to empirically explore the relationships between existing object-oriented coupling, cohesion, and inheritance measures and the probability of fault detection in system classes during testing. In other words, we wish to better understand the relationship between existing design measurement in OO systems and the quality of the software developed. The second goal is to propose an investigation and analysis strategy to make these kind of studies more repeatable and comparable, a problem which is pervasive in the literature on quality measurement. Results show that many of the measures capture similar dimensions in the data set, thus reflecting the fact that many of them are based on similar principles and hypotheses. However, it is shown that by using a subset of measures, accurate models can be built to predict which classes contain most of the existing faults. When predicting fault-prone classes, the best model shows a percentage of correct clas...

This paper presents a controlled experiment focusing on the impact of applying quality design principles such as the ones provided by Coad and Yourdon on the maintainability of object-oriented designs.

The availability of significant measures in the early phases of the software development life-cycle allows for better management of the later phases, and more effective quality assessment when quality can be more easily affected by preventive or corrective actions. In this paper, we introduce and compare various high-level design measures for object-based software systems. The measures

This paper aims at empirically exploring the relationships between most of the existing design coupling, cohesion, and inheritance measures for object-oriented (OO) systems, and the fault-proneness of OO system classes. The underlying goal of this study is to better understand the relationship between existing design measurement in OO systems and the quality of the software developed. In addition, we aim at assessing whether such relationships, once modeled, can be used to effectively drive and focus inspections or testing. The study described here is a replication of an analogous study conducted in a university environment with systems developed by students. In order to draw more general conclusions and to (dis)confirm the results obtained there, we now replicated the study using data collected on an industrial system developed by professionals. Results show that many of our findings are consistent across systems, despite the very disparate nature of the systems under study. Some of the strong dimensions captured by the measures in each data set are visible in both the university and industrial case study. For example, the frequency of method invocations appears to be the main driving factor of fault-proneness in all systems. However, there are also differences across studies, which illustrate the fact that, although many principles and techniques can be reused, quality does not follow universal laws and quality models must be developed locally, wherever needed.

A primary expected benefit of object-oriented (OO) methods is the creation of software systems that are easier to adapt and maintain. OO design patterns are especially geared to improve adaptability, since patterns generally increase the complexity of an initial design in order to ease future enhancements. For design patterns to really provide benefit, they must reduce the cost of future adaptation. The evidence of improvements in adaptability through the use of design patterns and other design structures consists primarily of intuitive arguments and examples. There is little empirical evidence to support claims of improved flexibility of these preferred structures. In this case study, we analyze 39 versions of an evolving industrial OO software system to see if there is a relationship between patterns, other design attributes, and the number of changes. We found a strong relationship between class size and the number of changes --- larger classes were changed more frequently. We also found two relationships that we did not expect: (1) classes that participate in design patterns are not less change prone --- these pattern classes are among the most change prone in the system, and (2) classes that are reused the most through inheritance tend to be more change prone. These unexpected results hold up after accounting for class size, which had the strongest relationship with changes. Keywords Design patterns, object-oriented design, software changes, adaptability. 1.

Design patterns are an important concept in the field of software engineering, providing a language and application independent method for expressing and conveying lessons learned by experienced designers. There is a large gap, however, between the aesthetic and elegance of the patterns as intended and the reality of working with an ultimately mathematically expressible system such as code. In this paper we describe a step towards meaningful formal analysis of code within the language of patterns, and discuss potential uses. The major contributions include: a compendium of Elemental Design Patterns (EDPs), a layer of seemingly simplistic relationships between objects that, on closer inspection, provide a critical link between the world of formal analysis and the realm of pattern design and implementation without reducing the patterns to merely syntactic constructs; an extension to the ς-calculus, termed ρ-calculus, a formal notation for expressing relationships between the elements of object oriented languages, and its use in expressing the EDPs directly. We discuss their use in composition and decomposition of existing patterns, identification of pattern use in existing code to aid comprehension, and future research directions, such as support for refactoring of designs, interaction with traditional code analysis systems, and the education of students of software architecture. 1. Problem Description Programming has historically been an exercise in the creation of hierarchical abstractions to manage complexity. As programming techniques have progressed in the field, language designers have continued to push the envelope of producing explicit constructs for those conceptual lessons learned in the previous generation of languages, and software architects have continued to build ever more complex and powerful abstractions. At the same time that these ab-

Measuring structural design properties of a software system, such as coupling, cohesion, or complexity, is a promising approach towards early quality assessments. To use such measurement effectively, quality models are needed that quantitatively describe how these internal structural properties relate to relevant external system qualities such as reliability or maintainability. This chapter has for objective to summarize, in a structured and detailed fashion, the empirical results that have been reported so far with modeling external system quality based on structural design properties in object-oriented systems. We perform a critical review of existing work in order to identify lessons learned regarding the way these studies are performed and reported. Constructive guidelines are also provided to facilitate the work of future studies, thus facilitating the development of an

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The assessment of the changeability of software systems is of major concern for buyers of large systems found in fastmoving domains such as telecommunications. One way of approaching this problem is to investigate the dependency between the changeability of the software and its design, with the goal of finding design properties that can be used as changeability indicators. In the realm of objectoriented systems, experiments have been conducted showing that coupling between classes is such an indicator. However, class cohesion has not been quantitatively studied in respect to changeability. In this research, we set out to investigate whether cohesion is correlated with changeability. As cohesion metrics, LCC and LCOM were adopted, and for measuring changeability, a change impact model was used. The data collected on three test systems of industrial size indicate no such correlation. Manual investigation of classes supposed to be weakly cohesive showed that the metrics used do not capture all the facets of class cohesion. We conclude that cohesion metrics such as LCC and LCOM should not be used as changeability indicators.

Design patterns are an important concept in the field of software engineering, providing a language and application independent method for expressing and conveying lessons learned by experienced designers. There is a large gap, however, between the aesthetic and elegance of the patterns as intended and the reality of working with an ultimately mathematically expressible system such as code. In this paper we describe a step towards meaningful formal analysis of code within the language of patterns, and discuss potential uses. The major contributions include: a compendium of Elemental Design Patterns (EDPs), a layer of seemingly simplistic relationships between objects that, on closer inspection, provide a critical link between the world of formal analysis and the realm of pattern design and implementation without reducing the patterns to merely syntactic constructs; an extension to the #-calculus, termed #-calculus, a formal notation for expressing relationships between the elements of object oriented languages, and its use in expressing the EDPs directly. We discuss their use in composition and decomposition of existing patterns, identification of pattern use in existing code to aid comprehension, support for refactoring of designs, integration with traditional code analysis techniques, and the education of students of software architecture.