This document proposes and demonstrates evolution storyboards, a new technique for visualizing software evolution over time. Evolution storyboards display the evolution of a software system through a series of panels that depict important events and periods in the system's lifetime. Nodes represent code elements and edges show code changes. Properties of the layout algorithm and approach are described. The technique is illustrated using open source systems and shown to help understand software structure, explain decay, and identify refactoring opportunities.

1. EPFLEPFL
Dirk.Beyer@epfl.chDirk.Beyer@epfl.ch
Dirk BeyerDirk Beyer
Simon Fraser UniversitySimon Fraser University
Dirk.Beyer@sfu.caDirk.Beyer@sfu.ca
Animated Visualization of
Software History Using
Evolution Storyboards
Ahmed E. HassanAhmed E. Hassan
University Of VictoriaUniversity Of Victoria
ahmed@uvic.caahmed@uvic.ca

2. Visualizing Software Evolution
• Static visualizations of evolution:
– fail to capture the dynamics of software evolution
• A movie visualization of evolution:
– is not easy to control by developers (who want to focus
on particular time periods, or parts of a system)
• We propose a visualization, evolution storyboards,
which strikes a balance between static and movie
visualizations

3. Storyboard
• Produced traditionally beforehand for
directors and cinematographers
• Used to study movie scenes and to uncover
potential problems before they occur

4. An Example Storyboard

5. Evolution Storyboard
• An evolution storyboard contains dynamic
panels
• Each panel depicts consecutively important
events and periods in the lifetime of long-
lived software systems

6. Our Graph Model
• Nodes: files/functions/subsystems
• Edges: co-change (from CVS)
• Layout: energy-based
A B
C D
A B
C D
C1
C2

7. Studied Systems
System Years Commits Nodes Edges
ArgoUML 8 10,108 20,247 57,036
PostgreSQL 9 7,882 9,086 35,809
Mozilla 6 9,950 11,754 30,938

8. Properties of
Our Layout Algorithm
• Related nodes are placed together, non-related
nodes are placed far apart
• Strongly connected nodes separate out from the
rest of the graph

9. Approach Overview
• To avoid blur and clutter:
– We ignore small movements of a node,
• if its degree did not change
– We do not highlight a node’s movement,
• if it did not move much (e.g. < 1% of panel size)
• if its degree is too small
– We use a “follow your neighbors” heuristic

10. Storyboard Colouring
• Authoritative decomposition:
– subsystems / directory
• Heat Map based on a node’s movement:
– Orange (moved in 40% of panels), Yellow
(30%), Green (20%), Gray (10%)

11. Panels in Evolution Storyboards

12. Panels in Evolution Storyboards

13. Benefits of Evolution Storyboards
• Spot good structure
– well separated nodes
• Explain decay symptoms:
– colouring patterns (separate/mixed colours)
• Highlight refactoring candidates:
– frequently moving nodes (using heat colouring)

14. Mozilla Storyboard
Compose
DB
MIME
Address Book
IMAP
NNTP
Parsing

15. Mozilla 1st
Panel in Storyboard

16. Refactoring Candidates (1/2)

17. Refactoring Candidates (2/2)

18. Conclusion
• Static visualizations of evolution do not capture
the dynamics of software evolution
• The approach has been applied to several large
software systems: Mozilla, ArgoUML,
PostgreSQL
• Evolution storyboards can help:
– Spot good structure
– Explain design decay
– Highlight refactoring candidates