1. A non-transitory computer-readable medium of a computer storing a modeling tool adapted for implementation by the computer for developing a hierarchical model of a market associated with a set of competing products, the modeling tool comprising a set of computer-executable instructions that when executed by a processor of the computer cause the computer to implement: an item definition module to provide a first display interface, the item definition module configured to generate a plurality of items for use by the modeling tool, and the first display interface configured to receive, from a user, an item definition for each of the plurality of items, wherein each of the item definitions includes one or more product attributes associated with the corresponding item; a structure definition module to provide a second display interface, the second display interface configured to receive item selection data and positioning data associated with the plurality of items from the user and the structure definition module configured to execute on the processor to create the hierarchical model defining a plurality of nodes at a multiplicity of levels successively removed from a root node using the received item selection data and the positioning data and to generate a graphical representation of the hierarchical model for display on the second display interface; and a structure validation module to detect that there are not errors in the hierarchical market model, the detecting including: detecting that all the item definitions associated with any of the plurality of items that are positioned on a first level of the hierarchical market model are mutually exclusive, detecting that the positioning data associated with the plurality of items in the hierarchical market model is consistent with the item definition for each item of the plurality of items, and detecting that all the item definitions associated with any of the plurality of items that are positioned on a second level of the hierarchical market model exhaust all transactions in a collection of transactions used to create the item definitions.