There is a special varient of the Biovision BVH format known as the ASK file ("ASK" stands for "Alias SKeleton") and was intended specifically to accompany Alias' Poweranimator SDL files which contain motion information for transformation nodes in Alias Poweranimator. The ASK file is meant to contain only skeleton information so does not contain channel specifications nor does it contain motion data. The ASK format is nearly identical to the BVH format except that the offset information is specified differently. In the BVH file the offset of a child segment was relative to its parents position. In the ASK format the offset information is in global coordinates, it's not relative to its parent. To get the same offset value as found in the BVH file you would subtract the position of the parent from the child. It was done this way because the ASK was intended as a format that could easily be edited by hand. It was expected that a user would inspect some other database (say an Alias animation file) and find the global coordinates of each segment in the hierarchy. These values were then entered by hand into the ASK file. If a BVH file where to be used the user would have to do a lot of subraction to create the offset information and it was decided to avoid that.
The SDL file (the Alias Scene Description Language format) is a compex format that can contain many different kinds of scene data information. It isn't possible to describe it here other than to say the SDL files used with ASK files are not complete SDL files, they are portions of an SDL file which describe just the motion of a single hierarchy of elements.