Constraint-based document layout for the Web

Constraints can be used to specify declaratively the desired layout of a Web document. We present a system architecture in which both the author and the viewer can impose page layout constraints, some required and some preferential. The final appearance of the Web page is thus the result of negotiation between author and viewer, where this negotiation is carried out by solving the set of required and preferential constraints imposed by both parties. We identify two plausible system architectures, based on different ways of dividing the work of constraint solving between Web server and Web client. We describe a prototype constraint-based Web authoring system and viewing tool that provides linear arithmetic constraints for specifying the layout of the document as well as finite-domain constraints for specifying font size relationships. Finally, we provide an empirical evaluation of the prototype.