1. A UML design system for creating a UML model of a user interface environment, comprising: at least one computer system, including: a system for defining use cases within the UML model, wherein the use cases are independent of each other; a system for associating an affinity representing a user-perceived relationship between use cases within the UML model, wherein the affinity is directional from an affinity use case to a target use case; a system for assigning a weight to the affinity within the UML model, wherein the system for assigning the weight assigns a first weight that dictates a strength of the affinity from a first use case to a second use case and assigns a second, separate weight that dictates a strength of the affinity from the second use case to the first use case; a system for incorporating affinity data into the UML model to influence use cases to be displayed in the user interface environment, wherein the affinity data includes assigned weights; and a system for determining whether the affinity use case should be appeared on a selected display type based on the affinity data.