Anyone who has worked on BRFplus and scanned SDN for answers must have heard about Carsten Ziegler. A savant on this technology, he is the co-author of this almost definitive work on the technology. With their vast experience in SAP, they have been involved in the technology since the formative years. That reflects in their writing as well.
The book covers all relevant topics in significant detail. Chapters on Functions and Objects are particularly illuminating. They are followed by the topics Rules and Expressions which are explored in detail. Some more details would have added more value because sometimes these concepts get intertwined in practice. Some novice users of the technology might find it difficult to connect the dots. Book also deals with performance, implementation and UI integration which adds immense practical value to the book.
This book starts with a blank slate as far as any process related knowledge is concerned. However, basic ABAP knowledge is required to use this book. As SAP is getting more and more object oriented, the same is reflected in this book as well. Hence, some OOP knowledge can be deemed necessary. One high point is that the code and logic explained in the book are easy to understand and can be implemented without much effort.
Overall the book is well drafted for both beginner and advanced users. Only low in this otherwise well-written book is that a small project covering all topics from a practical point of view could have been added for a more wholesome experience.