  Web archiving is the process of collecting portions of the Web to ensure that
the information is preserved for future exploitation. However, despite the
increasing number of web archives worldwide, the absence of efficient and
meaningful exploration methods still remains a major hurdle in the way of
turning them into a usable and useful information source. In this paper, we
focus on this problem and propose an RDF/S model and a distributed framework
for building semantic profiles ("layers") that describe semantic information
about the contents of web archives. A semantic layer allows describing metadata
information about the archived documents, annotating them with useful semantic
information (like entities, concepts and events), and publishing all this data
on the Web as Linked Data. Such structured repositories offer advanced query
and integration capabilities, and make web archives directly exploitable by
other systems and tools. To demonstrate their query capabilities, we build and
query semantic layers for three different types of web archives. An
experimental evaluation showed that a semantic layer can answer information
needs that existing keyword-based systems are not able to sufficiently satisfy.
