Internal and external quality in the evolution of mobile software: An exploratory study in open-source market

Context Mobile applications evolve rapidly and grow constantly to meet user requirements. Satisfying these requirements may lead to poor design choices that can degrade internal quality and performance, and consequently external quality and quality in use. Therefore, monitoring the characteristics of mobile applications through their evolution is important to facilitate maintenance and development. Objective This study aims to explore internal quality, external quality and the relation between these two by carrying out an embedded, multiple case study that includes two cases in different functional domains. In each case study, the evolution of three open-source mobile applications having similar features in the same domain and platform is investigated with the analysis of a number of code-based and community-based metrics, to understand whether they are significantly related to quality characteristics. Method A total of 105 releases of the six mobile applications are analyzed to understand internal quality, where code-based characteristics are employed in the light of Lehman’s Increasing Complexity, Continuous Growth, and Decreasing Quality laws. External quality is explored by adapting DeLone and McLean model of information system success and using community-based metrics, when data is available for the included releases, to derive a corresponding success index. Finally, internal and external quality relationship is investigated by applying Spearman’s correlation analysis on metrics data from 91 corresponding releases. Results The analysis of Lehman’s laws shows that only the law of Continuous Growth is validated for the selected mobile applications in both case studies. Spearman’s analysis results indicate that the internal quality attribute of ‘Understandability’ is negatively related to ‘Success Index’ for Case Study A and ‘LCOM’ is negatively related to ‘Success Index’ for Case Study B. No other significant relationship between the internal quality attributes and the Success Index is observed; but specific to community-based metrics, some significant relationships with code-based attributes were determined. Conclusion Our exploratory study is unique for the method it employs for exploring the relationship between internal and external quality in the evolution of mobile applications. Yet, our findings should be used with caution as they are derived from a limited number of applications. Therefore, this study should be considered to provide initial evidence for applicability of the method and a degree of confidence for repeating similar studies in wider contexts.