Declarative Web Applications

XForms is a web language which, as the name suggests, was originally designed for describing forms on the web. It has an number of unusual properties, such as separation of data and presentation, abstract input-output controls that allow for easy adaptation using style-sheets, and a declarative, invariant-based computation engine. After the release of the initial 1.0 version of XForms, it was quickly realised that with a small amount of generalisation, XForms could also be used to describe more general applications than only forms. And so was born version 1.1. This has since been widely adopted in industry (for instance the KNMI is entirely XForms-based, and XForms is an integral part of the Open Document Format ODF), and allowed us to gain experience in its use. One of the interesting pieces of experience is that you can write applications in XForms at about a tenth of the cost of using a language such as Javascript. This talk will present the essential elements of XForms, and then as an example, develop a mapping application that would otherwise require thousands of lines of Javascript. Steven Pemberton has been a researcher at the CWI since the early 80's. He has been active in the web since its beginning, organising two workshops at the first web conference in 1994, and chairing the first style sheets workshop at W3C. He has been involved in developing web technologies based on his research, and is co-author of many well-known technologies, such as HTML, XHTML, CSS, XForms, and RDFa, as well as a number of lesser-known ones.