A method of facilitating interaction between a user and a computer system using a product item having an interface surface, the interface surface having disposed thereon or therein coded data including a plurality of coded data portions, each coded data portion being indicative of an identity of the product item, the interaction being mediated by a sensing device, wherein the method includes: (a) associating the sensing device with the user; (b) in the sensing device: (i) sensing at least one coded data portion when the sensing device is placed in an operative position relative to the interface surface; and (ii) generating, using at least some of the sensed coded data, indicating data indicative of the identity of the product item and an identity of the sensing device; and, (iii) transferring the indicating data to a computer system; (c) in the computer system: (i) receiving the indicating data; (ii) generating, using the received indicating data: (1) product identity data indicative of the identity of the product item; (2) sensing device identity data indicative of the identity of the sensing device; and, (d) dissociating the sensing device and the user.