A framework to describe identifying characteristics of an item. Using this framework allows for changes to be made without documentation — as long as they align with the form, fit and function of the product. Form refers to physical characteristics including shape, size, dimensions, weight and other uniquely distinguishable characteristics. Fit is the ability of a product or subassembly to connect or become an essential part of another product. The function is the effective and reliable action a product or subassembly is designed to perform.