6. The method of claim 1 , wherein a first Item-ItemSelector Association array is a linear array of vectors, each index of the linear array corresponding to a different ItemSelector, and a vector uniquely associated with such index being a list of all Item reference values associated with such ItemSelector.
6. The method of claim 1 , wherein a first Item-ItemSelector Association array is a linear array of vectors, each index of the linear array corresponding to a different ItemSelector, and a vector uniquely associated with such index being a list of all Item reference values associated with such ItemSelector. 7. The method of claim 6 , wherein a second Item-ItemSelector Association array is a linear array of vectors, each index of the linear array being a reference value corresponding to a particular Item, and a vector uniquely associated with such index being a list of all indices of the first Item-ItemSelector Association array corresponding to ItemSelectors associated with such Item; further comprising obtaining a list of Items associated with a particular ItemSelector by reference to the first Item-ItemSelector Association array, and obtaining a list of ItemSelectors associated with a particular Item by reference to the second Item-ItemSelector Association array.