---Goals---
1. Given labeled data, explore different splits
   a. Select different features, and thresholds
   b. Suggest a feature and split
   c. Allow for backtracking
   d. Display the effects of splitting (how?)

2. Easy to navigate data
   a. Zooming and panning?
   b. Detailed view of selected patient, and path to that patient

3. Able to reference a tree created in the past
   a. Export as file?
   b. Save params in query params of the URL?

---Implementation---
Interaction and visualization -- d3.js?
Decision tree functions -- write own in js?


toy tennis data from http://www.cis.temple.edu/~giorgio/cis587/readings/id3-c45.html