Over the past few years, the demand for richer user interfaces and fast performance for web applications has also had its effect on enterprise web UI development. Solutions such as rich thin client frameworks and rich internet application (RIA) frameworks have emerged, alongside technologies like AJAX and Adobe Flex. At Siemens Corporate Research, our recent experience in developing a scalable enterprise web application with an agile methodology, however, has indicated that implementation decisions are often made without fully understanding the implications that the desired Ul concept and look and feel have on the implementation. This paper presents a conceptual Ul architecture and, for each aspect of the architecture, examines the types of requirements that should be gleaned from the various Ul requirements documents. We make recommendations to help bridge the gap between user interface design specifications and user interface architectural specifications, including impacts on implementation-level architecture.