1. A portal system comprising: an integration layer comprising a navigation service module residing on a first programmable machine, the navigation service module defining a connector interface and; a data layer comprising a plurality of application sources, each of the application sources creating an application-specific hierarchy, the plurality of application sources residing on one or more additional programmable machines that communicate over a network with the navigation service module on the first programmable machine, and an equal number of navigation connectors to the navigation service, each one of the plurality of application sources providing one of the navigation connectors by implementing the defined connector interface on the one or more additional programmable machines and by generating one or more navigation nodes that represent data objects in the each one of the plurality of application sources; and a presentation layer that resides on the first programmable machine and that comprises one or more navigation applications that obtain navigation information from the navigation service module, the navigation service module uniting the navigation nodes provided by the plurality of navigation connectors to provide a homogeneous view of navigation information from the plurality of application sources by uniting the application-specific navigation hierarchies from each of the plurality of application sources into a unified, consistent application hierarchy that is presented to one or more clients running on one or more client machines.