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| Type | Dissertation |
| Scope | Discipline-based scholarship |
| Title | Change distilling. Enriching software evolution analysis with fine-grained source code change histories |
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| Institution | University of Zurich |
| Faculty | Faculty of Economics, Business Administration and Information Technology |
| Number of Pages | 230 |
| Date | 2008 |
| Abstract Text | Software systems have to evolve over their life-cycle or they become progressively less useful. The reasons of why software is continuously changed are manifold: Features are added or adapted because of changing requirements; bugs have to be fixed because of faults in the software; or the software has to be migrated because of modernization. One negative effect of the continuing change is the software aging phenomenon. As software is changed from people unaware of the initial design concepts and, mostly, under time-pressure software becomes larger, more complex, and less understandable. As a result, in the last decade, several techniques have been developed to understand the negative impact of continuing change by analyzing change in general and source code change in particular. The approaches developed so far suffer from the coarse-grained information available for changes. They rely on data provided by versioning systems, which keep track of changes by storing the text differences of a particular file. Changes at the level of source code entities are not considered. In addition, a precise definition and a classification of source code changes are still missing. Both are key to extract and analyze source code changes, and eventually understand the negative impact of continuing change. We therefore claim: Extracting, classifying, and analyzing finegrained source code changes from the history of software systems provide useful insights into problems of continuing change and can identify support mechanisms to reduce them. The key contribution of this dissertation is change distilling, a methodology to define, classify, extract, and analyze fine-grained source code changes. Change distilling provides a taxonomy of source code changes which defines source code change types according to tree edit operations in the abstract syntax tree. Our change distilling algorithm applies tree differencing pairwise on subsequent versions of abstract syntax trees to extract the tree edit operations. We provide three empirical experiments to show the benefits of extracting finegrained source code change types. First, we analyze the source code and comment co-change behavior in the evolution of eight software systems. We show that in cases where comments are adapted to source code changes, the related changes happen in the same revision. We also show that in half of these software systems API comments are adapted several revisions after the source code change happened. Second, we explore whether certain change types appear frequently together. For that we use hierarchical agglomerative clustering to discover change type patterns and present a catalogue of change type patterns. The results from a commercial software system show that certain control flow changes are due to source code cleanup activities, that exception flow is used differently in different system parts, and that API convention changes are spread over many releases. Third, we investigate whether methods exist whose invocations are significantly more affected by context and update changes than other methods, and whether we can reveal change patterns among these invocation changes. We develop an approach that ranks how often context and update changes were applied to invocations of a particular method and whether these changes were bug fixes. In addition, we extract patterns of context and update changes to assess whether they can be used to provide valuable change suggestions. The results of our three software evolution experiments provide enough evidence that the analysis of change types helps in understanding software evolution and provides means to support developers in their daily work. |
| Other Identification Number | merlin-id:270 |
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