Constraint-based document layout for the Web

Constraints can be used to specify declaratively the desired layout of a We b document. We present a system architecture in which both the author and t he viewer can impose page layout constraints, some required and some prefer ential. The final appearance of the Web page is thus the result of negotiat ion between author and viewer, where this negotiation is carried out by sol ving the set of required and preferential constraints imposed by both parti es. We identify two plausible system architectures, based on different ways of dividing the work of constraint solving between Web server and Web clie nt. We describe a prototype constraint-based Web authoring system and viewi ng tool that provides linear arithmetic constraints for specifying the layo ut of the document as well as finite-domain constraints for specifying font size relationships. Finally, we provide an empirical evaluation of the pro totype.