Unlike low-level graphics libraries that quickly become tedious for visualization, Protovis defines marks through dynamic properties that encode data, allowing inheritance, scales and layouts to simplify construction. Protovis is free and open-source, provided under the BSD License. Skyrails Blog. Someone finally (thanks Christian) sent a mail in the skyrails-public mailing list, asking some questions, so I answered in the mailing list.
It'll just become an FAQ here instead. > I am aware of that skyrails is a sprout of a PhD research. A Periodic Table of Visualization Methods.