Algorithm Visualization: A Report on the State of the Field Clifford A. Shaffer, Matthew Cooper, and Stephen H. Edwards Department of Computer Science Virginia Tech Blacksburg, VA

Algorithm Visualization Timeline 1981: Sorting out Sorting, Ronald Baeker 1984: Balsa Late 1980s/Early 90s: Tango, XTango, etc. Mid/late 1990s to now: Java

Rationale Many faculty wish to use AVs Hundreds of visualizations are freely available on the Internet Studies on the effectiveness of AVs Many studies show no significant difference But AVs have been shown to help in some implementations One conclusion is that creating/using effective AVs is possible but not easy

Research Questions What AVs are available? How do educators find AVs? Who makes them? Is there adequate coverage? What is their quality? Is the field active, and improving? Is there adequate infrastructure for storing and disseminating AVs?

What AVs are Available? A collection of links available at the AlgoViz Wiki: Links to over 350 visualizations Nearly all AVs now written in Java Applets vs. applications Stand-alone vs. collections

How Do Educators Find AVs? Online repositories are not currently part of the picture Few AVs available from JERIC, SIGCSE, ACM DL, CITADEL, or other educational repositories Zero Google presence from those AVs that are in the repositories Various small collection sites exist (~20 AVs) Google search currently the most viable approach for typical educators visualization animation applet

Will We Find Them Again? May 29: 46 links. After 3 months: 4 lost (9%) 2 have permanent redirect links Nov 27: 1839 total links. After 3 months: 77 lost (4%) 162 redirects (in danger of being lost?) July 31: 251 links. After 7 months: 40 lost (16%) 13 redirect (in danger of being lost?)

Who Makes Them? Single authors, one-off implementations 10-15% Small shops, sustained over a few years Typically a faculty member and a few students 5-15 visualizations 30-40% Larger projects, longer term investment Team built, maybe funded integrated package or shared look-and-feel 50%

Is There Adequate Coverage? No Sorting, search trees, and linear structures overwhelmingly dominate Coverage for more advanced topics is spotty

What Is Their Quality? A majority have no pedagogical value These give the user no understanding of how the data structure or algorithm works Will be of little use in the classroom We would recommend less than one quarter of what we have seen for any purpose Even the better visualizations usually have serious deficiencies Animation only: Users are passive observers Tree structure visualizations tend to show what happens, but not how

Is the Field Active? Reported “last changed” date for sorting AVs by project

Is the Field Improving? Pros: A growing body of literature on best practices to create effective AVs Cons: No organized community Recent projects are no more in tune with coverage gaps than old projects No apparent movement in creating repositories

Future: Do We Need Repositories? Large repositories (ACM DL, CITADEL) organize by content, not delivery type So any AVs are buried in the papers, syllabi, lab exercises Google search could be sufficient… … if we had standardized search terms, and … if the distribution sites were stable

How Repositories Could Help Google search won’t help instructors who want to browse for good ideas Distribution sites maintained by individuals are unstable Curated sites can provide editorial guidance A repository can allow for community input on ratings, etc.

Future Needs: A Community Build a community In general, promote more interaction among developers Establish and disseminate best practices Ex: Open Source tools and procedures Establish a collection of good quality AVs Need some sort of review process Provide guidance to potential developers on coverage gaps Forums and other communications (conference?)

Contribute to the AlgoViz Wiki! Wiki: ( We would like to make this a community-driven site Easy opportunities for participation Provide new links Provide ratings Suggest papers Provide paper reviews

A Sample Wiki AV Entry