Navigation consistency in web site families

Abstract

Users accessing different but comparable web sites of some organizations, e.g., different departments of a university, expect them to have comparable content and provide for comparable ways to navigate through the content. To ensure such a similar look and feel, organizations may either define strict design rules to be met across all its web sites, with no room for site-specific modifications or, which is also frequent, only provide for a common entry point to entirely different sub-sites. Web Site Families offer a design approach that balances these two extremes. They allow specifying general requirements and they support site-specific modifications in that the general requirements can be specialized.Web Site Families organize related web sites in a hierarchy in which common design requirements for members at a lower level (e.g., department web site) are defined at the higher level (e.g., faculty level). Members at the lower level may specialize "inherited" requirements through extension, i.e., adding new links and pages, and refinement, i.e, replacing links or pages through a set of linked pages. The paper introduces navigation consistency as a design criterion that ensures that the specialized navigation requirements of a web site model adhere to the general navigation requirements of a more general web site model. Two kinds of navigation consistency are distinguished: Observation consistency, ensuring that any navigation according to the more specific model is observable as a correct navigation according to the more general model, and invocation consistency, ensuring that any link traversal (navigation) according to the more general model is also valid for the more specific model and achieves the expected effect.To assist web site developers and users, the paper presents necessary and sufficient rules to check for observation consistency and invocation consistency between navigation models of web site families.