Customising web information systems according to user preferences

Web Information Systems have to serve a variety of users with very diverse preferences regarding content, functionality and presentation. We first investigate the customisation of functionality at a high-level of abstraction, where possible action sequences are represented by an algebraic expression called plot, and user preferences give rise to equations. We show that the problem can be solved by applying conditional term rewriting on the basis of Kleene algebras with tests. By exploiting the idea of weakest preconditions such expressions can be represented by formal power series with coefficients in a Boolean algebra. This gives rise to a sufficient condition for termination based on well-founded orders on such power series. As confluence cannot be guaranteed, we propose critical pair completion to be used in order to enforce the desirable Church-Rosser property. In a second step we parametrise the actions and replace the Boolean conditions by first-order formulae. We show that still term rewriting can be applied, but termination and Church Rosser property become problems that will require manual interaction, in particular, as preference rules will make use of the parameters. On the other hand the presence of first-order conditions can be used to extend the customisation to the content.