Every piece has a way that it can move, something that makes it unique. A pawn can
only move one square forward unless it hasn't moved yet, it which case it can move two squares forward. The only object which usee the piece defs is the board. Because a piece def is not a general property of a piece, instead a specific thing that varies given a different piece type, piece defs are defined outside of the piece class. In my program I give them there own section of code to be archived. An unmistakable part of the game that makes it what it is. Without piece defs chess wouldn't be chess, it would just be an array of pieces with no meaning, moving without thought and without purpose.
The piece def can be one object or a group of small pieces of guide divided up, available for use throughout the program. This is what I have choosen, six classes with one statically defined sub routine defining a pieces defintion.