Supplementary material for the paper:

Clustering Software Artifacts Based on Frequent Common Changes (IWPC 2005)

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The following table compares layouts of co-change graphs created with the edge-repulsion LinLog energy model (described in the paper) and with the standard force model of Fruchterman and Reingold [1]. The figures show that the Fruchterman-Reingold model separates clusters less clearly (because it enforces uniform edge lengths) and has a strong bias towards placing nodes with high degree (i.e. nodes that participated in many change transactions and are drawn large in the figures) in the center (because it models node repulsion instead of edge repulsion). This is typical for state-of-the-art force and energy models, because they are not primarily designed for clustering.

The .png files are static pictures that can be viewed with standard web browsers. The .wrl files can be viewed with a VRML viewer (for example Cortona VRML Client, a plugin for standard web browsers). The advantage of the VRML files is that the names of graph nodes can be selectively shown and that one can navigate through the layout.

Additionally, the last column of the table provides the raw text dumps of the co-change graphs for all three systems. An edge {a, t} between an artifact node a and a change transaction node t with weight w is represented in such a file as a tuple (a, t, w). The weight of an edge is always 1, as discussed in the paper.


 Edge-repulsion LinLog layout
(from the paper) 		Fruchterman-Reingold layout
(for comparison)		 Co-Change graph
(raw text dump)
CrocoPat 2.1 Pat21.png, Pat21.wrl PatFR21.png, PatFR21.wrl CrocoPat-2.1.rsf
Rabbit 2.1 Rabbit21.png, Rabbit21.wrl Rabbit21FR.png, Rabbit21FR.wrl Rabbit-2.1.rsf
Blast 1.1 Blast.png, Blast.wrl BlastFR.png, BlastFR.wrl Blast-1.1.rsf

The artifact vertices are drawn as circles in the figures. The vertices for change transactions and the edges are omitted. The area of the circles is proportional to the degree of the corresponding vertice. The circles are colored according to the authoritative decomposition. Different subsystems in the authoritative decomposition correspond to different colors. (In the Blast visualizations, some colors are difficult to distinguish because of the large number of different colors.)

References:

[1] Thomas M. J. Fruchterman and Edward M. Reingold: Graph Drawing by Force-Directed Placement. Software - Practice and Experience 21(11): 1129-1164, 1991