Abstract: A method and apparatus for dynamically updating a user interface are described. A data model is stored locally in a processing system. A presentation document is generated in the processing system based on the data model and a source document written in extensible markup language. The user interface is rendered in the processing system based on the presentation document. In response to an event, the processing system causes a corresponding change to the data model, and then automatically or semi-automatically determines a set of parts of the presentation document which are invalid as a result of the change and updates only those segments that are invalid. The user interface is then rendered based on the updated presentation document.