This book is based upon the authors white paper, found on Rationals site, and it shows. The first half of the book is a complete waste of time, it summarises web technologies. If I wished to know about them, I would look into a dedicated book. If the first part is of any use to me, how on earth could I model something if I understand it so poorly, and if I do understand it, it's useless.
The second half explains how to model web pages, and is admittedly very useful, however the Whitepaper on Rationals site, covers much of the same information. Admittedly the bookl is more up to date, and slightly different, and what Rational would (I reckon) recommend, so it is probably necessary. It gives complete examples in the appendices which are useful, as many books on these sort of things, tend to avoid getting into anything resembling a useful example.
Basically the first half of the book is padding, because people don't like buying thin books. But the last half is good. If you need to model web pages, it's the only book I currently know about, and it *does* do the job well, when it gets round to it, so get it.
By the way, on the front cover it says 'Foreword by Grady Booch', I guess they must print this as standard, as the book doesn't even *have* a foreword. What a bunch of plonkers!