architecture - Book about Entity System?

I'm really interested about the capabilities of Entity System. I'm trying to search for a good book on this one, but failed.

I don't want to get lost on learning this paradigm so a book will be a big help. Can someone recommend a good book?

Also, is this language agnostic? Or are there languages that will have a hard time implementing this paradigm (eg. Objective-C)?

Thanks.

Answer

I learned about game entity systems through the book Game Engine Architecture by Jason Gregory. He discusses several implementations, ranging from class based to purely aggregate components, complete with examples. I highly recommend it, not just for that section, but for anybody who wants to know how to structure code for their game.

Edit: Just found this thread on Stack Overflow with tons of resources