Stephan Diehl

Identifying Refactorings from Source-Code Changes

Software has been and is still mostly refactored without tool support. Moreover, as we found in our case studies, programmers tend not to document these changes as refactorings, or even worse label changes as refactorings, although they are not. In this paper we present a technique to detect changes that are likely to be refactorings and rank them according to the likelihood. The evaluation shows that the method has both a high recall and a high precision - it finds most of the refactorings, and most of the found refactoring candidates are really refactorings

Graphs, They Are Changing

In this paper we present a generic algorithm for drawing sequences of graphs. This algorithm works for different layout algorithms and related metrics and adjustment strategies. It differs from previous work on dynamic graph drawing in that it considers all graphs in the sequence (offline) instead of just the previous ones (online) when computing the layout for each graph of the sequence. We introduce several general adjustment strategies and give examples of these strategies in the context of force-directed graph layout. Finally some results from our first prototype implementation are discussed.

Parallel Edge Splatting for Scalable Dynamic Graph Visualization

We present a novel dynamic graph visualization technique based on node-link diagrams. The graphs are drawn side-byside from left to right as a sequence of narrow stripes that are placed perpendicular to the horizontal time line. The hierarchically organized vertices of the graphs are arranged on vertical, parallel lines that bound the stripes; directed edges connect these vertices from left to right. To address massive overplotting of edges in huge graphs, we employ a splatting approach that transforms the edges to a pixel-based scalar field. This field represents the edge densities in a scalable way and is depicted by non-linear color mapping. The visualization method is complemented by interaction techniques that support data exploration by aggregation, filtering, brushing, and selective data zooming. Furthermore, we formalize graph patterns so that they can be interactively highlighted on demand. A case study on software releases explores the evolution of call graphs extracted from the JUnit open source software project. In a second application, we demonstrate the scalability of our approach by applying it to a bibliography dataset containing more than 1.5 million paper titles from 60 years of research history producing a vast amount of relations between title words.

The State of the Art in Visualizing Dynamic Graphs

Dynamic graph visualization focuses on the challenge of representing the evolution of relationships between en- tities in readable, scalable, and effective diagrams. This work surveys the growing number of approaches in this discipline. We derive a hierarchical taxonomy of techniques by systematically categorizing and tagging publica- tions. While static graph visualizations are often divided into node-link and matrix representations, we identify the representation of time as the major distinguishing feature for dynamic graph visualizations: either graphs are represented as animated diagrams or as static charts based on a timeline. Evaluations of animated approaches focus on dynamic stability for preserving the viewers mental map or, in general, compare animated diagrams to timeline-based ones. Finally, we identify and discuss challenges for future research.

Small patches get in

While there is a considerable amount of research on analyzing the change information stored in software repositories, only few researcher have looked at software changes contained in email archives in form of patches. In this paper we look at the email archives of two open source projects and answer questions like the following: How many emails contain patches? How long does it take for a patch to be accepted? Does the size of the patch influence its chances to be accepted or the duration until it gets accepted? Obviously, the answers to these questions can be helpful for the authors of patches, in particular because some of the answers are surprising.

Timeradartrees: visualizing dynamic compound digraphs

The evolution of dependencies in information hierarchies can be modeled by sequences of compound digraphs with edge weights. In this paper we present a novel approach to visualize such sequences of graphs. It uses radial tree layout to draw the hierarchy, and circle sectors to represent the temporal change of edges in the digraphs. We have developed several interaction techniques that allow the users to explore the structural and temporal data. Smooth animations help them to track the transitions between views. The usefulness of the approach is illustrated by examples from very different application domains.

Visual data mining in software archives

Software archives contain historical information about the development process of a software system. Using data mining techniques rules can be extracted from these archives. In this paper we discuss how standard visualization techniques can be applied to interactively explore these rules. To this end we extended the standard visualization techniques for association rules and sequence rules to also show the hierarchical order of items. Clusters and outliers in the resulting visualizations provide interesting insights into the relation between the temporal development of a system and its static structure. As an example we look at the large software archive of the MOZILLA open source project. Finally we discuss what kind of regularities and anomalies we found and how these can then be leveraged to support software engineers.

Dynamic graph drawing of sequences of orthogonal and hierarchical graphs

In this paper we introduce two novel algorithms for drawing sequences of orthogonal and hierarchical graphs while preserving the mental map. Both algorithms can be parameterized to trade layout quality for dynamic stability. In particular, we had to develop new metrics which work upon the intermediate results of layout phases. We discuss some properties of the resulting animations by means of examples.

Abstract machines for programming language implementation

We present an extensive, annotated bibliography of the abstract machines designed for each of the main programming paradigms (imperative, object oriented, functional, logic and concurrent). We conclude that whilst a large number of efficient abstract machines have been designed for particular language implementations, relatively little work has been done to design abstract machines in a systematic fashion.

Timeline trees: visualizing sequences of transactions in information hierarchies

In many applications transactions between the elements of an information hierarchy occur over time. For example, the product offers of a department store can be organized into product groups and subgroups to form an information hierarchy. A market basket consisting of the products bought by a customer forms a transaction. Market baskets of one or more customers can be ordered by time into a sequence of transactions. Each item in a transaction is associated with a measure, for example, the amount paid for a product. In this paper we present a novel method for visualizing sequences of these kinds of transactions in information hierarchies. It uses a tree layout to draw the hierarchy and a timeline to represent progression of transactions in the hierarchy. We have developed several interaction techniques that allow the users to explore the data. Smooth animations help them to track the transitions between views. The usefulness of the approach is illustrated by examples from several very different application domains.