The quality of conceptual models directly affects the quality of the understanding of the application domain and the quality of the final software products that are ultimately based on them. This paper describes a systematic literature review (SLR) of peer-reviewed conference and journal articles published from 1997 through 2009 on the quality of conceptual models written in UML, undertaken to understand the state-of-the-art, and then identify any gaps in current research. Six digital libraries were searched, and 266 papers dealing specifically with the quality of UML models were identified and classified into five dimensions: type of model quality, type of evidence, type of research result, type of diagram, and research goal. The results indicate that most research focuses on semantic quality, with relatively little on semantic completeness; as such, this research examines new modeling methods vs. quality frameworks and metrics, as well as quality assurance vs. understanding quality issues. The results also indicate that more empirical research is needed to develop a theoretical understanding of conceptual model quality. The classification scheme developed in this paper can serve as a guide for both researchers and practitioners.

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Context: Although various success stories of model-based approaches are reported in literature, there is still a significant resistance to model-based development in many software organizations because the UML is perceived to be expensive and not necessarily cost-effective. It is also important to gather empirical evidence in which context and under which conditions the UML makes or does not make a practical difference. Objective: Our objective is to provide empirical evidence as to which UML diagrams are more helpful during software maintenance: Forward Designed (FD) UML diagrams or Reverse Engineered (RE) UML diagrams. Method: We carried out a family of experiments which consisted of one experiment and two replications with a total of 169 Computer Science undergraduate students. Results: The individual data analysis and the meta-analysis conducted on the whole family, show a tendency in favor of FD diagrams and are significantly different as regards the effectiveness and efficiency of the subjects who participated and played the role of maintainers. The analysis of the qualitative data, collected using a post-experiment survey, reveals that the subjects did not consider RE diagrams helpful. Conclusions: Our findings show that there are some objective results (descriptive statistics or statistical tests) related to the maintenance effectiveness and efficiency in favor of the use of FD UML diagrams during software maintenance. Subjective opinions also lead us to recommend the use of UML diagrams (especially class diagrams) created during the design phase for software maintenance because they improve the understanding of the system in comparison with RE diagrams. Nevertheless, we can only assume that these results are valid in the context of Computer Science undergraduate students when working with small systems related to well-known domains, and other contexts should be explored in order to reaffirm the results in an industrial context by carrying out replications with professionals.

This paper presents the findings of a survey on the use of UML in software maintenance, carried out with 178 professionals working on software maintenance projects in 12 different countries. As part of long-term research we are carrying out to investigate the benefits of using UML in software maintenance, the main objectives of this survey are: 1) to explore whether UML diagrams are being used in software industry maintenance projects; 2) to see what UML diagrams are the most effective for software maintenance; 3) to find out what the perceived benefits of using UML diagrams are; and 4) to contextualize the kind of companies that use UML documentation in software maintenance. Some complementary results based on the way the documentation is used (whether it is UML-based or not) during software maintenance are also presented