Unifying navigation model

Systems and techniques to provide a unifying navigation model with a navigation service that provides an interface to information sources. In general, in one implementation, the technique includes: uniting navigation hierarchies from different application sources, and providing a unified navigation area based on the united navigation hierarchy. Uniting the navigation hierarchies can involve supplying a navigation service with a navigation object model that provides, to a presentation layer, a homogeneous view of navigation information from the different application sources. Providing the unified navigation area can involve displaying a navigation window in a portal presentation, the navigation window including navigation links to resources of the different application sources, and the navigation links being organized according to the united navigation hierarchy.