a very nice write up of talis at readwriteweb -

http://www.readwriteweb.com/archives/talis_semantic_web.php

"Basically, data in the Platform is stored in aptly-named structures
called 'stores', which allow data to be accessed using metadata (machine
 readable descriptors utilizing RDF). This data can then be accessed
and linked from the Web, allowing easy access to self-managed data
stores, while still enabling the RDF Semantic components to sort and
examine the data. Linked in with the semantic filtering and data-
management is a strong control of data and their interrelations. Any
element of the data can be matched and controlled, allowing access to
 relevant data rather than just returning simple search results. An
example Talis gives for this is in a retail context: a product can be
found in multiple stores; but using relevant retrieval, data can be
returned for a specific store.

"The upshot of the platform in combination with the Talis Community
License is that semantic mashups can be created. One such, a Firefox
plugin ... allows you to see which libraries across the UK
hold a copy of the book you happen to be looking for on Amazon."