I bought this book to get into XML. A lot of authors contributed to the chapters, so there might be good or bad chapters, but mostly the style of writing is pretty good and professional.
The book introduces XML itself, explains what metadata is and explains a lot of XML standards, such as XML Schema or Relax NG. It also contains some case studies that deal with XML meta data. There, the book stops being really helpful. A number of the introduced standards have never again made it to come up anywhere I looked (and I don't mean Relax NG here, I can't even remember their names). I think they tried to cover a lot of promising approaches and made a few wrong picks. That's ok, but it isn't really helpful if you're picking up the latter half of the book any later than 2001.
But I must say, I did pick up the first half of the book a few weeks ago to learn XML Schemas again and have a few examples, so I'm glad I have it on the shelf.