  The vision of the Semantic Web (SW) is gradually unfolding and taking shape
through a web of linked data, a part of which is built by capturing semantics
stored in existing knowledge organization systems (KOS), subject metadata and
resource metadata. The content of vast bibliographic collections is currently
categorized by some widely used bibliographic classification and we may soon
see them being mined for information and linked in a meaningful way across the
Web. Bibliographic classifications are designed for knowledge mediation which
offers both a rich terminology and different ways in which concepts can be
categorized and related to each other in the universe of knowledge. From
1990-2010 they have been used in various resource discovery services on the Web
and continue to be used to support information integration in a number of
international digital library projects. In this chapter we will revisit some of
the ways in which universal classifications, as language independent concept
schemes, can assist humans and computers in structuring and presenting
information and formulating queries. Most importantly, we highlight issues
important to understanding bibliographic classifications, both in terms of
their unused potential and technical limitations.
