This thesis presentsthe design and evaluation of an interface specification meta-language(ISML) that has been developed to explicitly support metaphor abstractions in a model-based, user interface design framework. The application of metaphor to user interface design is widely accepted within the HCI community, yet despite this, there exists relatively little formal support for user interface design practitioners. With the increasing range and power of user interface technologies made widely available comes the opportunity for the designof sophisticated, new forms of interactive environments. The inter-disciplinary nature of HCI offers many approaches to user interface design that include views on tasks, presentationand dialogue architectures and various domain models. Notations and tools that support these views vary equally, ranging from craft-based approachesthrough to computational or tool- based support and formal methods. Work in these areas depicts gradual cohesion of a number of these design views, but do not currently explicitly specify the application of metaphorical concepts in graphical user interface design. Towards addressing this omission, ISML was developed based on (and extending) some existing model- based user interface design concepts. Abstractions of metaphor and other interface design views are captured in the ISML framework using the extensible mark-up language(XML). A six-month case study, developing the `Urban Shout Cast' application is used to evaluate ISML. Two groups of four software engineers developed a networked, multi-user, virtual radio-broadcasting environment. A qualitative analysis examines both how each group developed metaphor designs within the ISML framework and also their perceptions of its utility and practicality. Subsequent analysis on the specification data from both groups reveals aspects of the project's design that ISML captured and those that were missed. Finally, the extent to which ISML can currently abstract the metaphors used in the case study is assessed through the development of a unified `meta-object' model. The results of the case study show that ISML is capable of expressing many of the features of each group's metaphor design, as well as highlighting important design considerations during development. Furthermore, it has been shown, in principle, how an underlying metaphor abstraction can be mapped to two different implementations. Evaluation of the case study also includes important design lessons: ISML metaphor models can be both very large and difficult to separate from other design views, some of which are either weakly expressed or unsupported. This suggests that the appropriate mappings between design abstractions cannot always be easily anticipated, and that understanding the use of model-based specifications in user interface design projects remains a challenge to the HCI community.