As suggested by Borgman [14-16], digital libraries should match and indeed dramatically extend traditional libraries. As such, they should be much more than search engine portals. Like any library they should feature a high degree of selection of resources that meet criteria relevant to their mission, and they should provide services, including search, that facilitate use of the resources by their target community. But, freed of the constraints of physical space and media, digital libraries can be more adaptive and reflective of the communities they serve. They should be collaborative, allowing users to contribute knowledge to the library, either actively through annotations, reviews, and the like, or passively through their patterns of resource use. In addition, they should be contextual, expressing the expanding web of inter-relationships and layers of knowledge that extend among selected primary resources. In this manner, the core of the digital library should be an evolving information base, weaving together professional selection and the "wisdom of crowds"