Yeah, what Andre said is correct.
The dot_line_plot exists for someone who has the data and doesn't want to lose time creating the x axis values for the points to exist.
It is still there for historical reasons, the scatter_plot was created after it and also does its job.
Download the trunk version and use the scatter_plot function or the ScatterPlot class.
We'll be releasing a new version soon.
Thanks for the interest,
Rodrigo