as an example: its functionality is voluntarily lim-ited to the basic function of bookmarking with tags, how-ever, the value of del.icio.us emerges from the massive amount
of annotated resources. Thus Web 2.0 services employ different measures for increasing user contributions and participations, for instance by building trust (e. g., oering users
to leave with an export of their data), by explicit licenses
(often open licenses such as Creative Commons), and para-doxically, by making content accessible through RSS syn-dication and APIs. Behind the user-provided data of Web
2.0 lies the Semantic Web [10] with its vision to make the
data currently hidden in databases available for usage by
machines.
As a result, Web 2.0 enables access to data at an unprece-dented scale, such as pictures (e. g., Flickr)
4
), bookmarks,
mapping data (e. g., Google Maps), but also indexed data,