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.