You might think there are just two sides in life, -1 and 1, but as soon as you start calculating long market value vs short market value for equities, for example, you (hopefully?) think man Sell Short is its own thing entirely, we can't just do positive and negative. 

The FIX protocol indeed defines 16 sides. Even though that specification is rather sprawling they did most things for a good reason. 

I look at the Order class and was a bit surprised that side is nowhere mentioned, at all. Seems potentially limiting?