First a qualification - I've known and respected Bob DuCharme for a couple of years, and so was rather delighted to find that he'd written a book on a topic that I have become heavily invested in for some time. The book was well worth the read.
While the book is not that thick, he manages to cover a lot of material in a clear, easy-to-read prose that nonetheless illustrates a great number of concepts, from how RDF itself works and the utility of OWL and OWL2 to the various tools that SPARQL provides for querying semantic triple databases. From data types and functions to various SPARQL patterns, he provides a compelling introduction into the topic, gives enough information to research further, and provides a number of insights that are useful even to those who have worked with SPARQL for a while.
He also includes a solid introduction into the SPARQL 1.1 UPDATE specification, which, in my opinion, makes SPARQL far more important not only as a query language but a general data access language. Given this is a relatively recent document, it's inclusion should make this a must read for anyone who is familiar with the older SPARQL spec but hasn't had a chance to take advantage of these major new tools.