u2014 the unique identifier of the product transmitter associated with the product using the same example the record of product 31 may identify product transmitter 30 aisle u2014 the set of shelves containing the product such as u201c 7r u201d for the right side of aisle 7 shelf u2014 the height of the shelf containing the product for product 31 this value may be u201c 1t u201d to identify the top shelf and for product 34 it may be u201c 2b u201d to identify the second shelf from the bottom distance u2014 the distance between the product 39 s location and the beginning of the aisle the value need not be exact but rather can correspond with a particular range using the same example the field may contain the value u201c m u201d which corresponds with product 31 being in the middle of the aisle contrasted with u201c b u201d and u201c e u201d which relate respectively to the beginning and end of the aisle this collection of information shall hereafter be referred to as the u201c product location database u201d the location of a product and its associated product transmitter may be readily obtained by querying the database in operation processor 23 initializes by querying the database 24 to determine the number of different product classes contained within the store the processor then queries the database.