Question on how to interpret Blender's Quaternions

I’m somewhat of a noob at Blender and I’m currently trying to write an export script to export skeletal animation. I don’t know how to interpret the quaternion data as it is stored in Blender’s IPO curves. I understand the benefits of using quaternions to do rotations, but I had always understood them as 4 scalar values. The IPO Curves in Blender’s actions have QuatW, QuatX, QuatY, QuatZ components, which makes sense,
but the values are BezTriple objects where I would expect a single floating point number. I’m not sure how this data is used to determine an orientation. I searched the net and the Blender forums but couldn’t find this information. Could someone explain this to me or point me in the right direction?