Data indexing using polyarchical indexing codes and automatically generated expansion paths. For a piece of data, an indexing code is received relating to a particular categorization or other indexing parameter. Based upon the indexing code, one or more expansion sets of codes are retrieved and applied to the piece of data. The expansion sets of codes may include indexing codes that relate to hierarchical levels of indexing. The expansion sets of codes may also include different expansion paths through the hierarchical levels of indexing. The polyarchical codes may include multiple cross-categorization of the data across the same or different levels of categories. They may also include multiple expansion paths in different directions across hierarchical levels of categories or indexing.