A method and apparatus are provided for generating a rate model (115) for use in determining a rate to be applied with respect to an instance of a product or service, system or process. The rate may relate for example to utilisation of a resource, for example to a charging rate to be applied with respect to use of a product or service. The rate model comprises: (i) data (205, 210) defining a rating space having at least one dimension defined by an attribute of the system, process, product or service; (ii) a rating vector definition comprising at least one rate parameter; and (iii) data (225, 230) which defines distinct regions in the rating space over which the defined rating vector is invariant, and which defines the respective invariant rating vector (235) for each distinct region (225, 230). A rate applicable to a particular instance of a product or service instance is determined by identifying a defined region (225, 230) containing the instance and hence the invariant rate parameter values (235) of the applicable invariant rating vector.