This evolution of library catalogs is like a dress rehearsal for moving library data from its storage silo in library systems and databases to the web of linked data. Through the Semantic Web, library data will link to select other data sources in order to provide more value and services for users. Conversely, other users and resources will be able to link to library data, thus making library data discoverable from a variety of points in web space. As information creation moves to the cloud, so will library services, not because libraries create their own cloud but because there will be no separation between libraries and the web.
Like the World Wide Web, the Semantic Web is about linking, but it adds the linking of data, not just documents. It also changes the nature of the link: Whereas the link between documents has no meaning other than “link,” in the Semantic Web, the links themselves have a specific meaning. Consider this citation example: In a standard document, a citation is simply a number in the text and a bibliographic citation at the end of the page. You don’t know why the author is citing that work other than what you can glean from the surrounding text. Using the richly semantic links of the Semantic Web, you could characterize each citation with a meaning such as “cites as evidence,” “disagrees with,” or “extends.” (Those examples are from an actual Semantic Web vocabulary, CiTO, or Citation Typing Ontology.)