OntoWeaver is our conceptual modelling methodology and a tool that support the specification and implementation of customized web applications. It relies on a number of different types of ontologies to declaratively describe all aspects of a web application. This paper focuses on the OntoWeaver customization framework, which exploits a user model, a customization rule model, and a declarative site model, to enable the design and development of customized web applications at a conceptual level. OntoWeaver makes use of the Jess inference engine to reason upon the site specifications and their underlying site ontologies according to the customization rules and the valuable user profiles to provide customization support in an intelligent way. The ontology-based approach enables the target web applications to be represented in an exchangeable format. Hence, the management and maintenance of web applications can be carried out at a conceptual level without having to worry about the implemen...