I think the best way to determine wether it is classed as a coaster is down to the manafacturer. If they label it as a coaster and it has the characteristics of one, then it is. A prime example of this is Cobra at CWOA, it has the characteristics of a rollercoaster, however the manufacturer labels it in the 'flat' category, and we are happy with that. On the other hand we have the Intamin half-pipe, very similar to the Disk-O, but labelled as a coaster by the manufacturer, again, we accept that. So the alpine disccusion works in the same way for me, If the manufacturer wants to label in either category, we should accept this, especially as they would have a valid argument either way.