Tags in Domain-Specific Sites - New Information?

If researchers use tags in retrieval applications they might assume,
implicitly, that tags represent novel information, e.g., when they
attribute performance improvement in their retrieval algorithm(s)
to the use of tags. In this work, we investigate whether this
assumption is true. We focus on the use of tags in domain-specific
websites because such websites are more likely to have a
coherent, discernible website structure and because the users that
are searching for and tagging pages in such a site may have
specific information needs (as opposed to the broad range of
information needs that users have when browsing/searching the
Internet at large). For this study, we assume that the application of
the same tag to multiple pages provides an indication that those
pages are related. To determine whether this indication of
relatedness is contributing new information, we first measure
whether pages with common tag(s) could have been deemed as
related based on site structure as measured by shortest
navigational distance between pages. Second, we measure
whether or not tags could have been determined algorithmically
based on standard tf-idf scores of terms on the page. Based on our
analysis of two different sites, we found that tags contribute novel
information that is not discernible from site structure or site/page content.