22. The method of claim 21 , wherein in a search for an item with specified Attributes, if for a given item any of the Attributes is of a Kind not implied by assignment of a Kind permitted for that item, or whose non-assignment is implied by the item's assignment of a Kind, the item is immediately excluded from the subset of results.
21. The method of claim 1 , wherein for a first Kind, one or more Kinds may be stored, such that assignment to an item of an Attribute of the first Kind implies assignment or non-assignment to the item of Attributes of the other Kinds.